Diss. ETH Nr. 7097
FIELO STUOIES
SPIOERS
(lI{ THE EC(IL(}GICAL
AS II.ISECT PREIIAT(IRS IiI
R(ILE (lF THE
AGR(IEC(ISYSTEMS
lABAl,tIl0itEB GßASSLAil0, IY|EAII0WS, ANII CEREAL FtELoSf
THESIS
submitted to the
SWISS FEDERAL INSTITUTE OF TECHNOLOGY
ZURICH
for the degree of Doctor of Natural Sciences
presented by
MARTIN NYFFELER
Dipl. lng.-Agr. ETH
born on March 25, 1950
citizen of Huttwil (Bern)
Accepted on the recommendation of
Prof. Dr. G. Benz, ETH Zürich, Referee
Prof. Dr. M. Schaefer, University of Göttingen, Co-referee
Prof. Dr. W. H. Whitcomb, University of Florida, Co-referee
aku-Fotodruck Zürich
1982
To my parents
ACKNOT.ILEDGE14ENTS
of the Dept. of Entomology, Swiss Federal
Technology, Zurich, proposed the interesting theme of this
thesjs and supervised it very critically and helpfully.
Professor Dr. M, Schaefer, Dept. of Zoology II, University of Göttingen,
Federal Republic of Germany, served as a co-referee.
Professor Dr. tl,H. }lhitcomb, Dept. of Entomology and Nematology, University of Florida, Gainesville, also served as a co-referee.
Professor Dr. G. Benz, Head
Institute of
Lecturer Dr. K. Thaler, Dept, of Zoology, University of Innsbruck, Austria,
checked my spider identifications and determined a few "difficult species".
Professor 0r. 1,J. Sauter, Dept, of Entomology, Swiss Federal Institute of
Technology, Zurich, gave me the permission to deposite specimens of all
spider species, described in this thesis, in the Entomological Collection.
Professor Dr. H.U, Thiele, Dept. of Zoology, University of KöIn, Federal
Republic
of
Germany, determined Carabidae.
Professor Dr. H.J. l,lüller,Oept. of Biology, University of Jena,
Democratic Republic, identifiecl cicadas.
German
Lecturer Dr. l,l. Dunger, State Museun of Natural Science, Görlitz,
German Democratic Republic, carried out the deterrninations of Collembola.
Dr. ll, Eglin, Natural History Museum Basel, Switzerland, identjfied
Chrysopi dae.
Dr.
I'1.
Meier, Swiss Federal Research Station for
Agronomy Zurich-Recken-
holz, determined aphids.
Dr. L. Gerig, Bee section, Swiss Federal Dairy Research Institute Liebefeld-8ern, identi fied bees.
0r. A. Nadig, Chur, Switzerland, camied out determinations of grasshoppers.
llr.
A. Fraser, School of Biological Sciences, University of East Anglia,
Britain, gave to me infomations on the ecoiogy of spiders in
Enslish cereal fields.
Professor Dr. F. KlOtzli and Lecturer Dr. A. Gigon, Geobotanical
Great
Institute,
The Ri,ibel Foundation, Swiss Federal
Institute of
Technology,
Zurich, gave to nn inforrnations on grasslands near Zurich.
0r. F. I'leilenmann, Swiss Federal Research Station for Agronor4y ZurichReckenholz, allowed me to undertake studies in cereal fields of the
research station,
Miss C. Vernazza was very helpful in translating this thesist and tlrs.
H. lilüller and Mrs. S. Lauber were typing it.
The author is very grateful to all these persons.
This research was supported by the Swiss National Science Foundation,
Grant 3.0020.76.
CONTENTS
1.
] NTRODUCTION
2.
MATERIALS AND
t1
Study area
t)
Bi
2.3.
Methods
2
METHODS
12
ed
12
12
otopes studi
of investigation
12
RESULTS
3..l.
3.1.1.
28
role of spiders as insect predators in
The
abandoned grasslands
28
Characterization of the biotopes and colonization
by spiders
Spider cormunities of abandoned grasslands
28
3.1.?.
3.1.3.
3.1.4.
3..l.5.
3.1.6.
Spatial distribution of spiders
3.1.7.
3.1.8,
3.1.9.
Spiders as predators of pest insects
Spiders as predators of beneficial insects
Predator-prey relations between spiders and adult
3.1..l0.
Prey
Prey capture
of
abundance and
42
spiders
46
dopterans
The
62
and energy
flow through
commun.ities
64
role of spiders as insect predators in
cultivated
The
62
62
64
killing rate (estimate)
the spider
28
daily activity
Niche breadth and niche overlap concerning food
of web-bu i 1 di ng spi ders
I ep i
3.2,1.
3.2.2.
3.2.3,
3.?.4,
3,2.5.
3.2.6.
of
Seasonal change
meadows
influence of
66
mowing
Spider cormunities of cultivated
Seasonal change
of
67
meadows
abundance
Spatial distribution of spiders
Prey capture of spiders
Niche overlap of spiders concerning food
67
76
76
83
90
3.2,7.
Predator-prey relations between crab spiders
and
wolf spiders
3,2.8.
Energy
cornmuni
3.3.
3.3..l.
3.3.2.
3.3.3.
3.3.4.
3.3.5.
3.3,6.
The
90
flow through the ground-dwe11ing spider
ti es
96
role of spiders as insect predators in
cereal fields
96
Inmigration into cereal fields
Spider conmunities of cereal fields
96
Seasonal change
of
abundance and
daily activity
96
100
Spatial distr"ibution of spiders
106
Prey captune of sPiders
Niche breadth and niche overlap concerning the food
il4
of
124
spiders
3.3.7.
3.3.8.
3.3.9.
Spiders as predators of pest and beneficial insects
Prey killing rate
Ener"gy flow through the spider cormunities
3.4.
New
of
reconds
of
Zurich
127
128
129
remarkabte spider
129
4.
DISCUSSION
l3l
5.
ZUSAMMENFASSUNG
149
6.
REFERENCES
150
1_
ABSTRACT
.l976-1979,
From
the ecology of spiders was jnvestjgated in abandoned
grasslands, cultivated meadows and cereal fields near Zurich (Switzerland). The spiders of such ecosystems ljve in two strata, (1) on the
ground surface, (2) in the vegetation zone. Different spjder conmunities
are found in the two strata.
In abandoned grasslands, the spiders live undisturbed all year round.
They can therefore bu.ild up relatively large populations in these bjotopes (near Zurjch about l0 spiders/mz; significantly higher values are
reported in literature). Cultivated fields, on the other hand, are
periodically
mown, whereby
the living space and the egg sacs of
many
spiders are destroyed. 0n1y relatively small spider populations I jve ,
therefore in the vegetation zone of cultivaled fields (about 1 spider/m'
in cultivated meadows and 0..l-0.6 spiders/mz in cereal fields). The
ground surface of cultivated fields is rather densel.y populated (.l5-42
in cultivated meadows and l0-50 spiders/mz in cereal fields).
The spiders in the vegetation zone of cultivated meadows and cerea.l
fields are primarily predators of Diptera and Homoptera. In the vegetation zone of abandoned grasslands, in addition honey bees and/or grasshoppers can form an essential part of the prey biomass of large web-building spiders.0n the ground surface of cultivated meadows and cereal
fields, the predominant spidens are mainly predators of small, softbodied insects (Collembola, Diptera, aphids etc.). From the food
analyses it follows that the spiders are predators of pest insects (e.9.
cereal aphids), indifferent species (most Diptera), and of beneficial
arthropods as well (honey bees, Chrysopidae, Coccinellidae etc.).
The energy flow (prey killed) through the spider communitjes of the
vegetation zone of abandoned grasslands can be high, e.g. >900 MJ/halyear
in a megaphorbe meadow. In comparison, the energy flow through the
spider corununities of cultivated fields is significantly.lower, e.g.
l.l-6.5 M,l/ha/year in cereal fields, and (0.5 MJ/ha/year in maize fields.
The energy f)ow through the ground-dwe1ling spider conrnunities of cultivated fields should amount to about l0-50 MJ/halyear.
Abandoned grasslands often are veritable spider paradises. In these
ecosystems, the spiders of the vegetation zone represent an important
predator" group. In the vegetation zone of cereal fields, on the contrary'
spiders do not seem to play a significant ecological role. Further studies
will show, to what extent the ground-dwe11ing spiders in cultivated
meadows and cereal fields are of ecological importance.
spiders/mz
2-
I
.
INTRODUCTION
Spiders are
among
the most dominant insect predators
of terrestrial
systems
.l974a; (TISCHLER,1965; VAN H00K, 1971; M0ULDER & REICHLE, 1972;
EDWARDS
et al.,'l976, a.o.).
eco-
SCHAEFER,
Under favorable^conditions they can
reach maximal d6lnslTies of up to iooo individuals/m2 approximately
(PEARSE, 1946; DUFFEY, 1962; !'IEIDEMANN, 1978). It has therefore been
supposed for some time thatspiders play an important role as stabilizing
agents and/or regulators of insect populations in agroecosystems, forest
ecosystems and othen terrestrial ecosystems.
Iast 20 yeans, numerous studies on the spider fauna in agricultural biotopes have been published ali over the world. Tables 1-4 give a
review classified according to continents and countries: Table I for
Europe, including the U.S.S.R., Table 2 for America, Table 3 for Asia and
During the
Table 4
for Africa and the 0ceanic-Australian
region.
In spite of the large
number of existing studies the significance of
the spiders as insect predators in agroecosystems is stjll Iargely
unknown. This could be attributed to the fact that up to the present
most stuies were limited either to the investigation of the species
composition and the seasonal occurrence of spiders in the field (sweep net
and pitfall trap collections) or to measurements of respiration, food
consumption tests, andprey preference trials in the laboratory. However,
the results of investigations on the nutrition of spiders in the laboratory cannot readily be transfemed to field conditions, because to some
extent spiders behave differently in the laboratory than in the field. In
the laboratory, spiders consume considerably more prey than would be
available under natural conditions (MIYASHITA, 'l968a, b; HAGSTRUM, 1970;
KESSLER, 1973; BREYMEYER & JOZWIK, 1975). Moreover, the prey composition
established by means of prey preference tests often does not correspond
to the prey conposition realized jn the field. Pest insects which are
regularly preyed on by a spider species in the laboratory may be entirely
missing in the prey composjtion of the field (temporal and/or spatial
isolatjon of predator and prey). Therefore the results of faunistic field
studies and of nutritional analyses in the laboratory cannot be combined
to a genuine whoie. There is a great danger that speculations disregarding
this ambiguity lead to wrong results. Correspondingly, the opinions on
the ecological relevance of spiders differ widely. BRiSTO!üE (1958) for
instance estimates
for
Great
Britain:
"Even
if
we were
so cautious as to
victims in the year to each spider, I calculate with
a very conservative estimate of the spider population for the country as
a whole that the weight of insects consumed annually in Britain exceeds
that of the human inhabitants". The Canadian ecologist TURNBULL ('l973)
gives an even higher estimate: "I have calculated from 37 published
censuses of spider populations that the mean density of spiders in a large
attribute a
hundred
variety of envjronments was 130.8 spiders/square meter, or 1
308 000/
hectare. If the food consumption of A. argentata were representative of
that of all spiders (which'it is not), the average total weight of food
consumed
per year by spiders would be
to these computations
F0ELIX (1979)
.....
42 490 kg/hectare". Referring
wrote: "However impressing these
-3-
Table
l. List of literature
in
on the spider faunas
including the U.S.S.R.
Country
Aus
tri
a
Agroecosystem
Authors
meadows
LUHAN (r979)
THALER
et
arable land
Be1
gi
Bu l
gari
um
Czechos I ovaki a
Federal Republic
STETNER
et al.
(r975)
(1977)
(1982)
DE cLERcQ (1979)
C0TTENTE & DE CLERCQ (1977)
verse crops
BoSMANS
& CoTTENTE (1977)
re
DELCHEV
ture
al fal fa
POLENEC
& KAJAK (1974)
(r968)
pas tu
pas
ugar-beet
meadows
MILLER
(cit.
MTLLER
(r974)
BoNESS
(r9s3)
SCHAEFER
(r958)
al fal fa
BONESS
(,l958)
cereal
BASEDot^1
BASED0W
s
BRASSE
as
para9us
vi neyard
onchards
verse crops
(1973)
& MTELKE (1977)
(1e35)
KrRN ( r978)
KRAEMER (1961)
(r976)
HEYDTMANN
TTScHLER
I
eys
(19s3)
(r9s8)
&
&
RAATTKATNEN
CHAUVTN
(1960,1967)
HUHTA
real
France
al
fal fa
German Democra-
meadows
BEYER (',|981 )
MULLER
grass-c1 over
mi xtune
BEYER
Republic
al fal
fa
cereal
s
('l974)
RAATTKATNEN ('l974)
RAATIKAINEN & HUHTA (1968)
ce
s
.l979)
(r975)
DTNGLER
NAToN
di
LUCZAK,
& HAAS (1979)
BoNESS
ci over
tic
.l978)
PÜHRTNGER
s
Germany
Fi nl and
(1977,
cereal
s
of
&
al.
orchards
di
a
THALER
THALER
agroecosystems
HUHTA
et al.
(r98r
(.l978)
)
GEILER (re63)
BEYER (1981)..
DTETRTCH & GoTZE (1974)
in
Europe,
-4-
Table
I (contin. ). List of l iterature on the spider faunas in
'in Europe, including the U.S.S.R.
Country
German Democra-
tic
Republic
Great Britain
Agroecosys tem
Authors
rape
BEYER
(r981)
BEYER
(re8r
)
kohl rabi
BEYER
(r98r
)
manrowstem kale
BEYER (r981 )
pasture
CHERRETT (r964)
DUFFEY (r962)
meadows
DUFFEY
(r974)
cereal
FRASER
(1982)
s
ugar- beet
s
aqroecosystems
Lo0KET (r978)
VICKERMAN
Hungary
DUNN
orchards
CHANT
al fal fa
BALoGH
trawbe
Nonvay
s
Pol and
pas
rry
&
SUNDERLAND
(I975)
(re49)
potato
(r956)
& LoKSA (]956)
TAKSDAL (1973)
& KAJAK (1974)
BREYMEYER (r967)
KAJAK (1960, 1962, 1971, 1978, 1980)
ture
DELCHEV
meadows
KAJAK & JAKUBCZYK (1975)
(1968, l97l)
KAJAK
et al.
al fal fa
LUCZAK (1975)
cereai
LUCZAK
s
(1974, 1975,
czAJKA & KANrA (1976)
potato
GALECKA (1966)
LUCZAK
sugar-beet
Sweden
Swi
tzerl
s
and
.l976, 'l979)
trawbe
rry
(r974,
.l975,
1976, 1979)
czAJKA & G00S (1976)
G00s (r973)
ALMQUTST (1981 )
meadows
BENZ & NYFFELER (1980)
MAURER (1974, 1975)
NYFFELER & BENz
cereal
NYFFELER
NYFFELER
NYFFELER
& BENZ (1979a)
& BENZ (I98OA)
& BENZ (1981e)
& BENZ (1979A)
(l9i9b, l98le)
U.S.S.R.
s
rape
NYFFELER
meadows
vTLBASTE (1965)
cereal
ASHTKBAYEV (1973)
potato
s
KoVAL (r976)
-5Iable 2. List of literature on the spider faunas in agroecosystems in America.
Coun
try
Brazi
Can
l
ada
Agroecosys tem
s
ugarcane
Au
thors
BARBOSA
et a1.
(1979)
(I966)
overgrazed pasture
TURNBULL
meadows
DoNDALE (1971, 1977)
DoNDALE & BrNNS (1977)
(1970, 1972)
DONDALE
Fox & DoNDALE (1972)
et al.
Panama
Peru
u.s.A.
&
DoNDALE (1979)
wheat
DoANE
orchards
DoNDALE (r956, r958)
(1979)
DoNDALE
PUTMAN (r957)
PUTMAN & HERNE (1966)
seed reservation
BREYMEYER
('l978)
(,l978)
et
al.
pasture
BREYMEYER
banana pl ants
HARRTSON
(r968)
cultivated fields
AGUTLAR (
r96s)
cotton
AGUTLAR
pas
ture
HO|,jARD
(r974)
& 0LIVER ('l978)
(r978)
PECK & l^lHTTCoMB
WHITCOMB
et
al.
(I963a)
woLcoTT (r937)
maedows
al
fal fa
woLcoTT (r937)
&
PTENKoWSKI (197'l)
& CHADA (r970b)
SCHLTNGER & DTETRTCK (1960)
l.lHEELER ( r973)
YEARGAN (1975a,b)
YEARGAN & C0THRAN (1974a,b)
YEARGAN & DoNDALE (1974)
H0WELL
MUNTAPPAN
ce
real
grain
s
HoRNER (r972)
MUNIAPPAN & CHADA (1970a)
sorghum
BATLEY
&
CHADA (1968)
sweet corn
EVERLY ('l938)
ri
w00DS
ce
soybeans
&
HARREL
(]976)
A HUGGANS (1962)
cuLrN & RUST (1980)
DEITZ et al. ('l976)
BLTCKENSTAFF
LESAR & UNZICKER
TURNTPSEED (1975)
l,lHTTCoMB (i980)
('l978a,b)
-6-
Table
2 (contin.). List of literature
in America.
on the spider faunas
Country
Agroecosys tem
Au
U.S.A.
cole
PII'IENTEL (196.l)
9Uar
RoGERS
s
ugarcane
agroecosystems
thors
&
HENSLEY
NEGM
cotton
in
&
HoRNER (1977)
et
.
al ( I 961 )
HENSLEY (1969)
et
BURLEIGH
a1. (1973)
CLARK & GLrCK (1961)
DoRRTS (r970)
JOHNSON
et a1.
(1976)
et al.
(1979)
(r943)
LEIGH & HUNTER (1969)
KAGAN
LOCKLEY
& STERLING (1979)
PFRTMMER (r964)
PIETERS & STERLTNG (1974)
McDANIEL
SHEPARD & STERLTNG (1972)
(1978)
STAM
b,lHITCoMB & BELL (.l964)
WHITCoMB & TADIC (1963)
et al.
!{HITC0MB
et a1.
(1963a,b)
ci trus
(r980)
MUMA (1973,1975)
orchards
LEGNER & oATMAN (1964)
McCAFFREY & H0RSBURGH (.l978' 1980)
SPECHT & DoNDALE (',I960)
diverse crops
BTLSTNG (1920)
t^lHITCoMB (1974, 1975)
CARR0LL
-7 -
Iable 3. List of literature on the spider faunas in agroecosystems in
Asi a.
Country
Agroecosys tem
Authors
India
mar ze
SHARMA
ri
ce
& SARUP (1979)
SINGH & SANDHU (1976)
KALoDE (1e76)
& MrSRA (',1975)
SAMAL
Israel
J
apan
& SrNGH (1975)
& KAUR (]974)
cotton
BATTU
ci trus
SADANA
gnapevi nes
SADANA
ci trus
sHULov ('1938)
apple orchards
MANS0UR
MANSOUR
ri
ce
&
SANDHU (1977)
et al.
et al.
HAI4AMURA
(1980a,b,c)
(1981)
(1969, l97l
HASHrM0r0 (1974)
HrßANO & KTRTTANT
IT0
et al.
)
(r976)
('l962)
KAKiYA & KIRITANI (I976)
& KTRITANI (1978)
(r975)
KAI',AHARA & KIRITANI ('l975)
KANG
KAWAHARA
KAWAHARA
et al. (1969, 1971)
(1977, 1979)
KIRITANI & KAKIYA (I975)
KIRITANT
KIRTTANT
KIRITANI
&
(1973)
(1972)
KAT,JAHARA
et al.
K0BAYASHT (1975, r977)
KoBAYASHT & SHIBATA (1973)
.l976)
KoYAMA (1972, 1975,
MIYAI
et al.
(1978)
OKUMA (1974,1977)
SASABA & KIRITANI (I974)
(1970)
SASABA
a1. (1973a,b)
SASABA
et
et
al.
SUZUKI & KIRITANI (I974)
TANAKA (1973, r975)
TANAKA
&
HAI'IAMURA
(1968)
ToYoDA & YoSHII'IURA (1966)
YAGTNUI4A (1965)
YAI'iANo ( 1977 )
cabbage
KAYASHIMA (1960)
oKUMA ('l975)
suzuKr &
taro
NAKASUJT (1976)
-8-
Iable 3 (contin. ). List of literature on the spider faunas in agroecosys tems
in
Asi a.
Country
Agroecosys tem
Authors
Japan
tea
KAIHoTSU (1979)
TERADA
TERADA
mul
Korea
berry
(re77)
et al.
KAYASHTMA
(1978)
(1967, 1972)
ci trus
KATHoTSU (1979)
NOHARA & YASUMATSU (-1965)
orch ards
HUKUSTMA (i96r )
HUKUSIMA & KONDO
oKUMA (',r973)
ri
CHOI
H0KY0
ce
(I962)
et al. (1978)
et al. (1976)
0KUMA et al. (1978)
PArK & KrM (1973)
(.1974)
PAIK et
mul
berry
People's Republic rice
of
PAIK
al.
et al.
(1973)
ANoNYM0US (1979)
China
Phi i i ppi
Tai wan
nes
& RARoS (1975)
IRRI Ann. Report (1973,1974)
IRRI Ann. Report (1976' 1977)
IRRI Ann. Report (1978)
LUCERo & RARoS (1975)
SALTNAS & RAR0S (1975)
ri
ce
GAVARRA
rl
ce
('l974)
CHIU
cHU & oKUMA (1970)
cHU & WANG (1972, 1973)
et al.
CHU
CHU
Thai I and
rl
ce
et al. (.l975, l976a,b,c)
et al . (1977)
0KUMA
oKUMA
(r968)
&
WoNGSTRI
('l973)
-9-
Table
4. List of literature
Africa
Country
Austral i
a
Egvpt
and
on the spider faunas in agroecosysterns in
region.
in the Oceanic-Australian
Agroecosystem
Authors
cotton
BrsHoP (1979, 1980, 1981)
BrsHoP & BL00D (r980)
R00M (1979)
orchards
DoNDALT (r966)
MacLELLAN (1973)
cl over
NEGM
cotton
granati
Fiji Islands
New
Guinea
South
Africa
et al.
t,llTESMANN
trees
(1975)
(1955)
TEMERAK
(198.l)
coconut
ToTHILL
et a1.
coffee
ROBTNS0N
strawberry
DIPPENAAR-SCH0EMAN
(1930)
& RoBINSoN (1974)
(1976,1979a'b)
_
.10 _
it would certainly be misleading to deduce from
that spiders play a significant role in pest control".
estimates may be,
them
In order to understand the effectiveness of spiders on the population
of insects, the species composition and the seasonal abundance
as well as their prey must be known. In every ecosystem
dynamics
of the spiders
there are diverse spider species and numerous prey species. According to
the rules of comb'inatorics an enormous number of potential predator-prey
interactions results from this fact, and a considerable part of them is
realized. To evaluate the ecological importance of the spiders as insect
predators, the predator-prey relations should be known. For this purpose,
the prey compositions and the feeding rates of the different spiders
should be determ'ined in the field. Finally, the ecological significance of
spiders could only be entirely appreciated, if the ecological importance
of the prey insects were known as well. However, only a few studies give
quantitative information on the
spiders'prey in the field (e.9. BILSING,
.l965a,
'l960;
1920i TURNBULL,
KAJAK,
SCHAEFER, 1974a; TURNER,1979). The
b;
R0BINSON
& ROBINS0N, 1970,1974;
lack of such studies on the feeding
ecology of the majority of the spider species of whole ecosystems is
probably due to the fact that up to now only few arachnologists have
taken the trouble of observing several spider species in the field while
they are feeding, as such observations require much time and patience.
The present study on
the ecology of spiders in cereal fields, cultjvated
grasslands near Zurich should at least in part fill
course of the investigations the following questions
meadows and abandoned
this gap. In the
have been asked:
(l)
l^lhich
spider species feed in
compos i
(2)
ti
How many
spiders per unit area feed in
(abundance
(3)
Does
the
meadows and
cereal fields (species
on ) ?
of
meadows and
cereal fields
spiders)?
abundance
of spiders
change
in the course of the year
(seasonal abundance)?
within the meadows and cereal fields do the spiders feed
(horizontal and vertical distribution)?
(5) At which time of day do the spiders feed (diurnal rhythms)?
(6) Wh'ich strateg'ies use the spiders to catch their prey (hunting
(4)
Where
strategy
)?
(7) What is the prey composition?
(8)
How much
prey per time unit do the spiders catch (prey capture rate)?
From points l-5 and 8 can be deduced to what extent the spider populations
exert a predatory pressure on the insect populations, as these points
supply information on the temporal and spatial distribution of the
predatory pressure and on the energy flow through the spider communities.
From points 6 and 7 can be gathered on which insect groups (pest specjes,
beneficjal species, indifferent species) the spiders act as predators.
-il-
before, numerous diffenent spider-prey interactions are
possible in an agroecosystem. Therefore, since even the gatherjng of the
data necessary for the evaluation of the interaction of just one spider
species with one prey species needs much time' the investigation of all
predator-prey interrelations within an ecosystem would far exceed the
scope of a doctoral thesis.
As mentioned
investigation of the populat'ion biology and feeding ecology of the
difficulty. For the vagrant hunting spiders
(e.9. Lycosidae, Salticidae) the stationary population densities and the
feeding ecology can be established only with great difficulty. Because of
their extraintestinal digestion it is not possible' for instance' to carry
out stomach content analyses as for birds, reptiles, amphibians and fishes.
Hunting spiders must therefore be observed in the field during long
perjods of time. 0n the other hand, the population densities and feeding
ecology of most web-building spiders can be determined relatively easily,
as many ecological processes take place in the easily observable webs. Fot"
The
diverse spider species varies in
this
reason, mostly web-building spiders have been observed,
122.
MATERIALS AND METHODS
2.1. Study
area
investigations were conducted in meadows and cereal fields on the outskirts of the city of Zurigh in the years 1976-1979. The study anea
The
of agricultural farmland at 395-600 metres
level (Fig. 1),41% of it being arable land and 53% meadows.
covers approximately 40 km'
above sea
0n the cultivated area the foilowing crops were grown: Wheat' barley,
rye, oats, maize, rape, sugar beet, field beans and vegetables. In 1975,
the cereals (excluding maize) occupied about 54%, maize (grain, silage
and green maize) about l3% of the tilled area.
The study area
is located in the transition
zone between
the
Western
climate and the Eastenn European continental climate.
Turtch (47.2v northern latitude) has a mean annual temperature of 8.8oC
and an annual variation of temperature of 17.8"C. Table 5 gives informations on the temperature and precipitation conditions during the four
years of the study. All climatic values were furnished by the Swiss
Meteorological Institute (tleather station Zurich).
European oceqnic
2.2, Biotopes studied
From 'l976
to
1979, studies were made
in
abandoned grassland bjotopes,
cultivated meadows and cereal fields on the outskirts of the city of
Zurich, The term "cultivated meadow" was used to express a contrast to
the "uncultivated meadow-land" (megaphorbe meadow Al, dry meadow A2).
"Abandonedgrasslands"means formerly cultivated land whjch for any
reason has not been tilled, fertilized or mown for some time or is
altogether abandoned. The biotopes are described in Tables 6-7.
The locations of the cultivated meadows where the studies were carried
out are described in Table 8. Most cultivated meadows in the region of
Zurich ane fertilized and mechanically mown several times a year.
Tne wheat, barley, rye, oat, and maize fields investigated are briefly
characterized in Table 9. The areas of the cereal fields ranged from
0.5 to 3 ha. They are not treated with insecticides in the region of
Zurich. However, herbicides are used in the maize fields. Pitfall trap
studies were made in winter wheat fields on the territory of the Swiss
Federal Research Station
2.3.
Methods
2.3.'l.
The
for
Agronomy
at
Zurich-Reckenholz.
of investigation
family and species composition of the spiders
2.3.1.1. Direct observatjons in the vegetation zone of cereal fie'lds
The cereal fields were visited periodically. The composition of the
fo1 i age-dwel 1 i ng spi der fauna was i nvesti gated by di rect observati ons '
All observation data were recorded. 0f sorne species, only
genus could be ascertained by this procedure.
the
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.-t92.3.1.2.
jn
the
Sweep net samples
an-d cul-ti vated meadows
vegetation zone of abandoned grasslands
ing spiders of abandoned grasslands and cultjvated
collected by means of a sweep net with an upper diameter
a length of 75 cm..l979.
Sweep net collections were made in June,
July, August, and September of
The single sweeps were counted. The
collected spiders were carefully taken out of the net with the help of
preserved
tweezers, killed and
in 70% ethanol. For every sample, the time
of day and the number of sweeps were recorded, In order to have
comparable data, the data were later converted into "number of spiders/
100 single sweeps".
The foliage-dwell
meadows were
of 40 cm and
2.3.'l.3. Pitfall trap studies in cultivated
The spider fauna on the ground surface
fields was studied by means of pitfall
meadows and
of cultivated
cereal fields
meadows and
cereal
traps. Transparent plastic
beakers (upper diameter 7 cm, height 7.5 cn) were used as traps; they
were completely sunk into the ground until the upper rim was level
with the ground surface. Each beaker r{as filled with 70 nl of 4%
formalin, and a touch of a detergent was added to reduce the surface
tension. The traps were not protected by a rain shelter, They were
emptied at intervals of l-2 weeks. In the laboratory, the spiders were
washed
in water and then preserved in
701 ethanol.
pitfall trap studies were made in a winter wheat fjeld on
the territory of the Swiss Federal Research Station for Agronomy ZurjchReckenholz. The experimental field had an area of 2 ha approximately,
Thereon, a screen of 45 pitfall traps was set up (Fig. 2). The shortest
In
1977, the
distance between two traps was 20
m.
1978 and 1979 respectively,6 more pitfall traps were set up
same field, In addition to this,6 other traps were set up in a
In
cultivated
meadow
in
in
the
Zurich-Höngg.
2.3.1,4. Determination of the spiders
The spiders collected were identified in the laboratory under a stereomicroscope. Genital preparations were made of female spiders which
could not definitely be determined by the morphology of the epigyne
alone. For this purpose, a piece of the^genital area which contained the
epigyne was macerated for 2 hours at 7O'C in a l0% solution of K0H.
Subsequently the preparation was washed in water and ethanol and then
enbedded in Euparal as a permanent mount. These genital preparations
were then studied and compared with the illustrations of the vulvae in
the books. The following publications served as keys: BLANKE (1976),
DAHL (r93r), DAHL & DAHL (1927), HARM (r97r), LoCKET & MILLTDGE
(1951/53), LOCKET et al. (1974), REII"I0SER (1937), ROEl'lER (1928),
TONGI0RGI ('l966), and t,JIEHLE (193t, 1937, I953, 1956, 1963).
The determination of 99 of Pardosa agrestis (l.lestr.) presented diffjculties. There is a danger of nistaking them for 99 of Pardosa montjcola
(C1.). Accor"dins to L0CKET et al. (1974), the width 6? th-e e[iljfrä(posterior margin) is 0.36-0.48 nm in P. monticola, and 0.48-0.78 nm
for P. agrestis. However, in a samp)e of-FT9-ilom a winter wheat
field, measured by myself, the postenior margin of the epigyne was
0.51-0.63 mm (P = 0.56 i 0,04 nxn), indicating that the species is
P. agrestis.
-20-
6
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!.o9
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ts
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-21 The nomenclature according
to
MAURER
('1978) was used. Samples
of
each
spider species determined by myself were verified by Dr. K. Thaler,
University of Innsbruck, Austria. A few species djfficult to identify
were determined by Dr. K. Thaler. At least one specimen of each spider
species was deposited
in the Entomological Collection of the Swiss
Federal Institute of Technology Zurich (Curator: Prof. Dr. V{. Sauter).
2.3.2. Invest'igation of the spider densities
?.3.2.1. Estimate of the relative density
Relative densities permit the comparison of different biotopes and
seasons 1ilÜuleneene, I976). Retative densities weie found by
means of the sweeping technique (number of spiders/100 sweeps) and pitfall traps (number of spiders/week/trap).
different
2.3.2.2. Estimate of the absolute density
The spider density in abandoned grassland, cultivated meadows and cereal
fields was investigated by means of the "square method". For this
purpose, the spiders were counted within squares in several places of
the field, In the vegetat'ion zone, a square frame of m x m was used.
0n the ground surface square frames of 0.2 m x 0.2 m,0.33 m x 0.33 m,
and of 0.4 m x 0.4 m were used.
I
I
not be applied to wolf spiders, as their
iocomotory activity is very high. The density of adult wolf spiders
therefore estimated by direct observation.
The square method could
2.3.3. Investigation of the seasonal
change
of
abundance
of
was
spiders
The seasonal occurrence of the spider species in the vegetation zone of
cereal fields was recorded by simple observations in the fields. The
foliage dwelling spiders of abandoned grassland and cultivated meadows,
on the other hand, were captured by sweeping with the net in different
seasons. Infonnation on the seasonal occurrence
their nunbers was derived from these sneeps.
of the spiders
and
The spiders caught in pitfall traps furnished informations on the
seasonal occumence of ground-dwelling spiders.
2.3.4. Investigation of the daily activity of spiders
The locomotory and feeding activity of the various spider species in
the field was recorded at different times around the clock. At night,
a flashlight was used.
-222.3.5, Investigation of the spatial distribution of spiders
2.3.5,.l. Investigation of the horizontal distribution of spiders
The dispersion index was calculated from the data collected by the
square method ( see 2. 3. 2. ) . The hori zontal di stri buti on of the spi ders
in the vegetation zone and on the ground vras established in this way.
The
distribution of the spiders in
MORISITA's index
space has been estimated using
independent of the size of the
The index of M0RISITA has been calculated
(I6)
of aggregation
.l974).
sampling unit (P00LE,
from the following equation:
n
n !.a_ xi(xi-l)
I önn
=F *.1 (f
x.-l)
'L
I
i-l
where
+h
i""
xi is the number of jndividuals in
and I x. is the total number of individuals in all the
i=l '
n is the
sample,
-
samp r es .
The fol1owing
I"ö < I
Iu = I
Is t'l
',
l_1
number
n
of
samples,
relations are valid:
uniform distribution,
random
distribution
(Poisson distribution),
aggregated distribution
the significance of the deviation of 16 from I, is
tested by calculating F as follows:
After
P00LE (1974)
I^(t
ö.4
i=l
x.-l)+n-I
1,
x.
i=l
I
E_
n-l
The value
of F is
compared
(with v, =@, v2 = n - l).
to a table of the F distrjbution
the
-232.3.5.2. Investigation of the vertical distributjon of
spiders
in the vege!a!ign
zone
of
orb-weaving
abandoned grasslg-nd
For each of the different orb-weaving spider species the vertical
distance from the ground to the orb hub was measured.
2.3.6. Analysjs of diversity
For the calculation of the diversity index (H') the
(also cailed
Shannon-Weaver
SHANNON-WIENER
formula
formula) of the information theory was used:
s
H'=-to.lno..
i=l
of species, pi = re'lative frequency of the ith species,
0.0 to 1.0.
To test the significance of the difference between two H'-values, the
t-Test was used as indicated by P00LE (.1974).
The diversity index (H') does not shor,, if its value is caused by a high
number of species with irnegular distributjon or by a low number of
species with regular distribution. Therefore, a supplementary measure,
the evenness (E) after PIEL0U (1966) is calculated:
where S = number
measured from
r-
H'
Hru"
The value of E ranges from 0 to
evenness (i.e. the mone regular
H'
In
s
+1. The higher the value the greater the
the distribution).
2.3.7. Investigation of the prey composition of spiders
2.3.7.1. Investigation of the prey composition of web-building sp'iders in
the vegetation zone of abandoned grassland, cultivated meadows,
and cereal fields
Which insect groups were caught in the spiders'webs at different times
of day and night was detennined by means of continuous observations in
the field.
During the night, the webs were observed in the light of a dirmed electric
torch. Care was taken not to influence thereby the behaviour of the
spiders and thein prey. To some extent the prey items were determined and
counted in the field, and the observation data recorded. In some cases
the prey iterns were collected from the webs with tweezers, and preserved
'in 70* ethyl alcohol. They were counted under the stereo-microscope. 0f
some important pney groups samples were
determi nati on .
sent to specialists for exact
-242,3.7,2, Investigation of the prey composition of hunting spiders (crab
spiders) in the vegetation zone of abandoned grassland, cultivated meadows, and cereal fields
During both day and n'ight the vegetation zone was thouroughly searched
for hunting spiders that were feeding. The prey items were determined
either directly in the field or later on in the laboratory.
2.3.7.3. Investigation of the prey composition of web-spiders 9n
the
for ground-dwelling spiders that v,ere
of the sma'll size of these spiders and their prey, such
studies could be made only during daytime. As before, the prey items
were determined either directly in the field or later on in the
laboratory. Samples of some important prey groups were sent to
special ists for identification.
The ground surface was searched
feeding.
Because
2.3.7.4. Investigation of the prey composition of diurnal hunting
d
cereal fields
l^lo1f spiders were caught in the field by hand collections with a transmeadows and
parent plastic beaker (7 cm upper diameter). Spiders with prey were
ki11ed, preserved in alcohol and later determined in the laboratory
under a stereo-microscope along with the prey. l^lolf spiders were only
observed in the daytine, as the dominant species (Pardosa spp.) are
diurnal (see 3.2.3.2. and 3.3.3.2.). 0f some important prey groups,
samples were sent to specialists for accurate deterrnination.
2.3.8. Investigation of the prey capture rate of spiders
2.3.8.'l.
0rb-weaving spiders
Two methods
Method
were used
to study the prey capture rate:
l: Direct observation in the field.
advantage
The numben
lock. This
of insects caught
method has the
of furnishing accurate data on how many insects a spider
It is, however, very time-consuming.
captures per day.
2: Many orb-weaving spiders rebuild their web every day. For
such spider species, the number of prey/web was counted at a time of the
day when the webs were filled with prey. This number gives an estimate
of the real capture rate which may be slightly higher, however' as sometimes single sma'll insects are already consumed during the day and
others get caught only after the prey has been counted. This method,
though less accurate than dinect observation, is far less time-consumMethod
i ng.
2.3.8.2. l,lolf spjjers
(1969, 1970) developed a method by means of which the prey
capture rate of wolf spiders can be calculated, if the feeding frequency
in the fjeld and the duration of feeding measured in the laboratony are
EDGAR
known.
-25the feeding frequency of the spiders, wolf spiders were
caught in cultjvated meadows and cereal fields on different days. In
the case of each captured spider it was recorded whether it had a prey
or not.
To determine
In order to measure the duration of feeding of wolf spiders, adult
males and females of P. agrestjs were caught in a winter wheat field
and brought into the TäEoraTory: There, they were confined singly to
circular petri-dishes (9 9 cm, height 1.5 cm) with a moist filter paper
on the bottom. At room temperature, the spiders were fed with aphids,
small bugs, Diptera, and spiders of about the same size as those
captured by the spiders in the field. The tine spent on the consumption
of one prey item was measured.
This method is suitable
crab spi dens , too.
for the evaluation of prey capture rates of
2.3.9. Calculation of the niche breadth and niche overlap
concerning
In order to examine to what extent the coexisting spider species use the
available food resources in conmon, the overlap and breadth of the food
compositions was determined. For this purpose, a resource matrix was set
up (MOHLENBERG, 1976), In our niche system, the compared spider groups
are looked upon as resource users and the components in the spiders'
prey are considered as resource classes. The overlap coefficient Cl was
calculated by means of the forrnula of MORISITA (1959), modified by
H0RN (1966):
z
i
L
*.u.
l-l
e^=, i=l ,
r*i*:vi
i=]
i=l
'
is the total numben of food items, xi and yi are proportions of
the ith item in the prey compositions of spiäer spääies x and y. The
values of Cl range from zero to i,0 (from entirely different to identica'l prey composition). According to ZARET & RAND (1971) one assumes that
Ctr values >0.60 ind.icate a considerable overlap. In the present study,
the njche overlap could not be calculated at species level, as only the
order or family of most prey items were determined. Therefore, the overlap values calculated in this thesis are probably overestimated
compared with the overlap determined at species leve1.
This over'lap index has been applied for the comparison of predators'
prey compositions by other authors, too (ZARET & RAND,1971i 0BRTEL &
where S
HoLrsovA, 1976).
Bi was calculated after LEVINS (1968), applying the
fol lowing forrnula derived from Simpson's index:
The niche breadth
-26-
B.
1
I
n^
t o.'
i=t
In this formula p- is the proportion of the ith of n resource
used by
a spider Species.
2.3.'l0.
ComDarison
of sDider
communities
categories
of d'ifferent locations
of two spider c-onmunities the "overlap index" (Cru)
(1970) was used. The formula is as follows:
For the comparison
after
SCH0ENER
I - o.5I
1n.,5
-
n.,*l
of species j of the species
This index ranges from 0 (no over1ap) to I (total overlap). This index, too, was used for the comparison
of ipider Communities of different locations by CURTIS (1978) and bv
where pii and pik are the proportions
conrmunities in ihe locations i and k.
SCHAEFER
& KoCK (1979).
2.3.1.l. Estimate of the energy flow through spider cammunities
The different pathways in a spider's energy budget are as follows: 0f
the "prey kil.led" only a part reaches the alimentary canal (= "prey
consumed"); the rest is not fed by the spider" (= "prey not consumed").
0f the präy consumed a part is absorbed by the gut and assinilated in
the body 1= "prey assimilated"); the rest is eliminated as "faeces".0f
the assimilated prey a part'is lost by "respiration" and "secretions"i
the rest remains for "production".0f these six components of the
energy flow, only the energy-input into a spider community ("prey killed"
and/ör "prey consumed") could be determined or calculated within the
framework of this thesis.
In the vegetation zone the "prey killed" by the large web-building
spiders can be studied easily by direct observation. Therefore, jn the
vegetation zone the energy flow was calculated on the basis of "prey
kiiled".0n the ground surface the "prey killed" by the small web-building spiders could not be studied easily. For that reason, in the
determination of the energy flow through the spider communities the
"prey consumed" C was calculated theoretically (C calculated as a
function of the weight of a spjder, see below).
2.3.'l,l..l. Vegetation zone
the knowledge of the prey capture nates and population densities,
the prey kill ing rate (number of prey items/ha/time unit) of. the.spiders
could bä calculited (see 3.1.1.l. and 3.3.9.). From the prey killing rate
the energy flow through the foliage-dwelling spider communjties was
calculatÄä by conversing the number of prey.items'into weight of prey
From
(kg prey/ha/time unit) and weight of prey into Joule or Megaioule
(MJ/ha/time
un'i
t)
.
-27The
to
caloric value of soft-bodied insects
approximately
JozwlK, i975).
5.44
J/mg
fresh weight
(sma11 Diptera, aphids) amounts
(vAN H00K, 1971, BREYMEYER &
2.3.11.2. Ground surface
Following LUCZAK (1975) the daily consumption (C) of one spider was
calculated after the equation of EDWARDS et al. (1972), generally
applicable to invertebrates:
loo C = loq 0.071 + 0.725 loo X
.
where C is expressed as callspider/day and X is the caloric content of
the body of a spider (1 mg dry weight - 5.8 cal = 24.3 J).
The daily energy flow E. (= "prey consumed") through the gnound-dwel1ing
web-building spider confrunity was estimated after the fornula:
Ec=C D'
is the density of the spiders (tl/*2).
The mean fresh weight of a ground-dwelling web-building spider was
assumed to be 2.5 mg. This is the fresh weight of one micnyphantid
spider with a body length of 2-2.5 rm (HEYDEMANN, 1962). In application
of this equation the average consumption of one micryphantid spider
in
which D
was calculated
to be 5.22 cal/day.
Approximately 80% of the killed prey is consumed by spiders (EDGAR, l97l;,
M0ULDER & REICHLE, 1972i t^l0RKaAN, 1978).
Hence follows the energy flow Epk ("prey killed"):
E.
= 'l.25
pKc
E
2.3..l2. Statistical anal is of data
In most cases the data collected in the field refer to frequencies.
Such
data have an assynrnetric distribution. If data have a symmetric
distribution one gives the arithmetic mean i (t SE) as characteristic
va1ues of the random samples. 0n the contrary, for assymetric
distribut'ions one should give the median | (t confidence interval) as
characteristic values of the random samples (SACHS, 1974). However, a
perusal of the renowned journals "Ecology", "Oecologia", "0ikos",
"J. Anim. Ecol.", "Nature" and "Science" has^ shown, that in most field
studies the mean value i and not the mediani was calculated. In the
'literature mainly the following characteristic values of random samples
are given: i r SD, i t SE, i t 95% C.L.
Therefore, in order to make the results of this thesis companable with
those of the literature, i 1 SE was given as characteristic value of
random samples.
For the comparison
(sAcHS, r974).
of
tlvo mean values nonparametnic tests were applied
-283.
RESULTS
3.1.
3.1.
The r"ole
of spiders as insect predators in
abandoned grasslands
I. Characterjzation of the biotopes and colonization by spjders
In biotopes with plants the spiders live in two zones: in the vegetation
zone (= foliage-dwelling spiders) and on the ground surface 1= grounddwelling spiders). In the two zones different spider families are found.
In abandoned grasslands, only the foliage-dwel1ing spiders were studied
within the
framework
of this thesis.
The abandoned grassland biotopes studied were mostly uncultivated
meadowland, shooting-grounds and future building sites overgrown with
high grass, unmown stripes of grassland along field borders and river
banks (see Tables 6-7). The vegetation zone of these grassland biotopes
is heterogenous, It is composed of grasses on the one hand and of herbs
and weeds (Cirsium arvense (1.) Scop., Rubus sp.) on the other hand.
Some of these grasslands are interspersed with single shrubs.
grassland is only little influenced by men. As spiders live
or less undisturbed in such biotopes' they are found in relatively
Abandoned
more
in the vegetation zone.
the
investigation of the spiders' density in the vegetaThe result of
high densities
two abandoned grassland biotopes (megaphorbe meadow Al and
A2) was 8.8 and 9.6 spidersfmz respectively between mid-May
and the end of May, and 10.6 spiders/mz in A2 at the beginning of Ju1y.
The estimate in Al in the beginning of September resulted in 9.4
spiders/m2 as well. This neans that in 1979 the spider density in the
vegetat.ion zone of both abandoned grassland biotopes was relatively 2
constant from May til September and amounted to about l0 individuals/m-.
tion
dry
zone
of
meadow
3.i.2. Spider
communities
of
abandoned grasslands
. Spi der conrnuni ty of bi otope Al
family composition of the foliage-dwelling spider community of the
megaphorbe meadow AI was investigated by means of the sweeping method
and is sunrnarized in Tables l0-ll, together with the reiative densities
and the age structure of the spiders. If we consider the total (June to
September), we find the following results: spiders belonging to the six
3. I . 2. I
The
famil ies Tetragnathidae, Pisauridae, Micryphantidae, Araneidae,
Salticidae, and Agelenidae prevailed in the sweep net samples (89% of
all spiders, g0% of the adult spiders). Tetragnathidae were found
most frequently. What the tables do not show is the fact that more than
two thirds of the captured spiders were females.
In Table 'l2, the species composition of the foliage-dwelling spiders
occurring in location A1 is represented. The table shows that the five
species Tetragnatha extensa
arcuata
(1.),
Hylyphantes
nigritus (Simon), qYlrgha
FTiaury_4jigu-f-r-l rej.T-
prevalled in thi iweep net samples (>80% of the total). T. extensa and
H. n'igritus were the two species most frequently captured.
The spider community of location Al consisted to a considerable degree
of species of medium to large size. Argiope bruennichi (Scop.), Araneus
Table
.l0. Family
composition in
zone
of the
.l979.
of the spider fauna in the vegetation
Al at different dates in summer
was investigated by means of sweep net
%
megaphorbe meadow
The composition
collections.
Immature and
adult spiders were
counted,
12.6.
28.6.
17.7.
14.8. 20.9.
Total
Spider family
N=434
N=81
7
N=950
N=906 N=649
N=3756
Tetragnathi dae
30.65
2.07
13.59
26.27
8,?9
3. 00
3. 00
L 84
0.92
5.99
00
00
4.38
Pi
sauri dae
Mi
cryphanti dae
Arane i dae
SaI
ti
ci dae
Agel eni dae
Li nyphi i dae
Thomi si dae
Cl ubi oni dae
Theri di i dae
Di
ctyni dae
Phi I odromidae
Unident. spiders
Total
I
42.23
.l5.06
I
5.75
13.71
8.45
3
.92
1
.71
2.57
3.67
1.96
0.98
00.0 100.0
16
0.95
2.63
8.42
4.32
4.21
3.47
1.89
1.16
2.00
0.32
0
3.47
I
00.0
51.31
7 .24
21.73
4.31
4.78
0.92
I .69
0.77
2.62
0.15
0.46
0.15
3.85
6l .48
57.
9. 38
10.49
3.42
8.94
0.99
0.33
L99
0.88
0.33
0.55
0.22
0.99
I
00.0
I
00.0
50.88
9
.80
9.77
9.72
6.87
?.66
1
.97
I . 86
I.86
.l.73
0.?9
0.08
2.50
r00.0
-30-
Table
ll. Relative density of immature and adult spiders in the vegetation zone of the megaphorbe meadow Al from June to Septenber'1979. i = immaturestages, a=adultstages, t=total
Number
Spider family
I 2
-
Araneidae
Tetragnathidae
-
Linyphiidae
4 - Micryphantidae
9.6
2.3
lt.9
?.12.7
1.5
214.2
0.4
0.8
1 .2
36.2
0.4
36.6
0
1.2
1.2
0.8
2.7
3.5
'I
.9
24.2
6.9
3l .1
6. 5
0.4
6.9
0.8
3r.5
t.?
32.7
3. I
0
3. I
3. s
t
0.4
22.8
16.0
I
?.8
96 .6
a
23. B
12.0
26.6
108.6
'|
2.6
6.6
a
0
0
2.6
6.6
l l.6
0.2
0.6
4.4
11.8
5.0
2.4
2.8
5.2
t.z
i
t
I
t
6 - Agelenidae
16.0
22.4
a
5 - Theridiidae
August
i
t
0
1.6
3.8
i
2.6
8.0
a
0
0
2.6
8.0
t
7 - Dictynidae
1
0
0.6
8 - Salticidae
i
5.0
6.2
a
2.2
?.0
8.2
t
9-
Thomisidae
i
I.6
3.0
0.6
3.6
I
0
0
i
0.4
20.4
a
t
i
1.4
1.8
0.4
20. 8
0.8
2.?
a
0
0
t
l0 I
| -
12
-
Philodromidae
Pisauridae
Clubionidae
t
Unidentified spiders
i
Total
*
Developmental stage
7.2
0.8
0.8
a
of T.
sweeps
July
a
t
3
of spiders/l00
June
0.8
22
3.8
6.6
43. 8
168. 4
43.0
?1 .6
86.8
190.0
33t.2
17 .4
348.6
extensa not distinguished
in
September
5.0
9.0
14.0
*
166.5
0
5.5
5.5
70.0
0.5
70.5
0.5
0
0.5
0
3.0
3.0
1.5
l l.0
4.5
15.5
2.0
0.5
2.5
0.5
23.5
0
23.5
8.0
0.5
8.5
12.5
30.l.0
23.5*
324.5
September
-3] -
Table 12. Species composition
of the spider fauna in the vegetation
zone
of
megaphorbe meadow Al in summer 1979. Species investigated by
means of sweep net collections.0nly adult spiders are listed in
the table. The numbers in parentenses behind the names correspond
the
with the family-numbers in Table ll.
Spider species
Araneus di adematusa ( I
)
Araneus quadratus (1)
Nuctenea cornuta
Argi ope bruenni
Meta segmentata
(l)
chi
(1)
(i)
Tetragnatha extensa (2)
0
0
2
U
0
t09
Tetragnatha pinicola (2)
I
Tetragnatha spe".b 1Z;
Pachygnatha clercki (2)
9
Linyphia triangularis (3)
Floronia bucculenta (3)
0
Disnodicus bifrons (4)
Hylyplantes nigritus (4)
Erigone dentipalpis (4)
Enoplognatha ovata (5)
Neotti ura bimacul ata (5 )
Agelena
gracilens (6)
Evarcha arcuata (8)
Heliophanus flavipes (8)
Xysti cus
cristatus (9)
mirabilis
0
I
57
0
0
t4
0
ll
0
2
t
Xysticus kochi (9)
Pisaura
0
(11)
7
Clubiona reclusa (12)
0
Clubiona neglecta (12)
0
Total
215
00
l0
00
00
00
80
00
12
00
00
00
20
44
0t
211
60
00
13
6l
03
00
62
20
t0
164
58
21
9
't08
0
0
4
?
I
0
I
I
0
t4
2
52
0
0
2
0
0
I
2
9
0
2
0
0
I
I
0
0
J
0
0
0
7
5
t8
9
0
0
0
I
I
0
J
0
0
I
0
0
45
100
8
3
2
14
301
I
14
I
'11
2
3
1?4
I
16
20
I3
60
7
6
3
t8
3
I
632
a Species not rare, often observed but never caught with the sweep net
b St".nunr without median light patch
1.27
0.47
0.32
2.22
47.63
0. t6
2.22
0.16
1.74
0.32
0.47
19.62
0.16
2.53
3. 16
2.06
9.49
l.il
0.95
0.47
2.85
0.47
0.16
100.0
-32Cl., Araneus diadematus Cl., Agelena gracilens C.L. Koch, and
P. mirabilis were the largest spiders found in Al (see Table 13). The
Targe we5:5[ilding spiders A. bruennichi, A. quadratus and A. giaci]ens
were only rarely and A. diadematus never caught with the sweep net
(Table I2). These four species were however rather frequent in location
A1 (see also Table 22). This probably signifies that large web-building
spiders are underproportionately represented in sweep net samples.
quadratus
3.1.2.2. Spider conununity of biotope A2
In the dry meadow 42, also, more than two thirds of the adult spiders
in the vegetation zone were females. Tables l4-15 show the
family composition of the spiders found in this location. From the totals
of Table l4 (right column) results that spiders belonging to the seven
fami I ies Thomi sidae, Sal ti cidae, Mi cryphanti dae, Tetragnathidae,
Pisauridae, Theridiidae and Araneidae predominated in the sweep net
samples (89S of ail spiders,96% of the adult spiders). The two spider
families Thomisidae and Salticidae, whose members hunt their prey without
caught
webs, were caught most frequently.
Table l6 represents the species composition of the foliage-dwel1ing
spiders occurring in location A2. The table shows that in the sweep net
samples the six species Tetragnatha pinicola L. Koch, H. nigritus,
flavlEilnäInT, and
Enoplosnatha ovatä (cl .)@
xysE?FcrTsETus (ct.) pre?ominäEa llTd7--ofthe-6EfT Most frequent
were the two species E. arcuata and X. cristatus.
of species of medjum size
(see Table 13). A. bruennichi, Aculepeira ceropegia (l'lalck.), and
The spider cormunity was thus mainly composed
i
.
mi rab
iIi
s werä-[fräläiEffi sFlZEilli-AZi-5[l-Eached
on I
y
re I a t i ve 1 y
Gil'-äffilTlEs.
3.1.2.3.
Comparison
of the spider conmunities of the two abandoned
grassland biotopes
The distance between
the two locations Al and A2
is 7 km. In accordance
with the differing levels of humidity, the moisture-loving T.
extensa
more frequent in Al, while in A2 the dryness-loving T. pinicola is
more often found. In both locations, however, the same spider families
were encountered, only in different percentages. In both locatjons' the
adult stages of more than 20 species could be caught by means of
the sweep
and identified. Twelve species, namely A. bruennich'i,
Meta segmentata Cl., T. pinicola, Linyphia triangu-laris C). il. nigritus,
is
net
'
E. bvata, N. bimaculata, E. arcuata, H. flaviles, Xysticus cristatu!' ._
xy=Ecus kocli-froreTi; ana p. rnTraUiTis occurrea ln uotti biotopes (Tables
7-fi4--I6-l;-oTl y one i nrnatu räTpETfrEi-Tf the i nterest i ng j umpi n g sp i der
Myrmarachne formicaria (Deg.) was found in each location.
Diversity (H') and evenness (E) were lower in AI than in A2 (Table.l7)_. The
difference'beiween the diversity indices H'41 and H'42 is statistically
significant (t-test, p<0,05). The lower diversity in the more humid Al
can be explained by the fact that only two species were hi9h1y predominant in Al , namely T. extensa and Hr_!-glj!:.
establish the similarity of the spider communjties of the two
locations Al and A2, SCHOENER's "overlap index" C.il was calculated.
To
-33-
Table
'l3.
Body
length (mm) of the adult spiders, whjch have been observed in
lands, cultivated meadows and cereal fjelds near Zurich.
abandoned
Informations compiled from literature (mainly after
LoCKET
& MIL-
LTDGE, 195r/53).
Spider
species
I
fimbriatus 13 -20
mirabilis 12 -.l5
gracilens l0 -15
ceropegia ll.5-14
bruennich.i ll -14
quadratus 9 -l 5
A. diadematus l0 -12
A. labyrinthicg I -12
T. extensa
8 -1 I
T. montana
6.5-10
8.5
A. alsine
N.cornuta
6 -8.5
6 -8.5
C.reclusa
7
E. arcuata
6 8
I'--!9$1
C.neglecta 6 -8
P. amentata 5. 5- 8
M.segmentata 5 -8
P. clercki
6
X. cnistatus
6 -7
P.agrestis
6 -6.5
T.obtusa
5 -7
L.triangularis 5 -6
T.pinicola
5 -6
P.cespitum 5 -6
H. flavipes
5 -6
P. palustris
4.5- 6
E.ovata
5 -5.5
H. auratus
4.5-6,5
P.pullata
4 -6
A. cucurbitina 4 -6
A.opisthographa 4 -6
D.
P.
A.
A.
A.
A.
d
9
Spider
3
12
7.5-12.5
6.5
4
6 -8
4.5- 8
8 -9
6 -9
6.5- 8
6
5 -8
5 -6
5 -6
4 -5
4.5
6 - 6.5
5 -6
5 -6
4 -5
4.5
3.5- 5.5
5 -6
4.5- 5
4
3 . 5- 4
4.5- 5.5
3 -4
3 -4
4 - 4.5
3.5- 4
-l
3.5-
4
species
I
hortensi s
4 -5
mengei 3.5-5
F. bucculenta 4
T. impressum 4 -4.5
E. angulatus 4 -4.5
3.5-5
M. pusilla
P. rufus
3.5-4
3 -5
A. sturmi
M.acalypha 4
A. riparia
3.5
H. sanguinea 3 -3.8
T. varians 2.5-3.5
N. bimaculata 2.5-3.3
H.nigritus
3
P. Ssgeeri 2.5-3
2.5-3
D. puella
D. uncinata 2.5-2.8
0.agicatus
2.5
0. tuberosus 2,5
2.5
0. fuscus
P. convexum 2.3-?.5
2 -2.5
E. atra
humilis
2 -2.5
L.
gracilis
2 -2.5
B.
D. bifrons
2 -2.3
T. vagans 2 -2,2
E. dentipalpis 'l.8-2.5
'l .8-2.5
D. pusilla
M. rurestris 1.8-2.2
T. boesenbergi ?
].5
P. oblitun
d
L.
3
M.
3.5-5
-4
4
2,5-3.5
4
3
3
3.5
2.5
3
-3.3
3
2.3-2.8
2.5-3
2.3
2.5-3
? -2.8
2 -2.5
2.3
2
-2.3
?
2.3-2.5
2 -2.5
1.8-2
'l.5-.l.8
l
8-2
1
.5-2
1.8-2.5
2
1.8-2.2
1.8
L5
-34-
in % of the spider fauna in the vegetation
of the dry meadow A2 at different dates in sununer 1979.
The composition was investigated by means of sweep net collections. Irmature and adult spiders were counted.
Table 14. Family composition
zone
Spider family
Thomi
Sa l
M
i
ti
s
i dae
ci dae
cryphanti dae
Tetragnath i dae
Pi
sauri dae
Theri di i dae
Aranei dae
Di
ctyni dae
Li nyphi i dae
C
l ubi oni dae
Lycos i dae
Ageleni dae
Philodromidae
Unident. spiders
Total
1
'?:3:
N=236 N=lt5
N=296
27.54
27.12
5.5t
8.05
4 .24
16 .95
7.63
00
0.42
0.85
0. 85
00
0.42
0.42
51.86
12.54
2.71
8.14
I 0. 85
5.08
2.03
0.34
1.36
0.34
0.34
0.34
00
4.O7
20.87
46.96
4.35
3.48
6.96
I .57
2.61
2.61
0
0.87
0
1.74
00.0 00.0
1
1
00.0
17.s.
Totar
N=368 N=281
22.83
18.21
14.95
15.49
8.97
1.63
1.90
2.99
1.63
I.36
0
0.27
9.78
N=t296
7.83 26.85
32.03 24.07
25.27 ll.73
3.56 8.80
7 .64
5 .69
1.07 5.7]
7.83 4.32
4.63 L93
0.36 l.16
0.36 0.69
0.7r 0.46
0.]5
0
0.08
0
0.68 6.33
1
100.0 100.0
100.0
-35-
of immature (i) and adult (a) spiin the vegetation zone of the dry meadow A2 from
to August 1979. t = total number of spidens.
Table 15. Relative density
ders
June
Nunber
Spider family
I -
J
Araneidae
2 - Tetragnathidae
3
-
Linyphiidae
of spiders/100
July
une
0
I.4
1.2
1.2
0.2
1.4
0.3
4.8
ll.4
1.2
'LI
0
I.4
4.8
It.4
0.1
0.4
0.4
0.8
0.8
0.4
0.8
0.8
10.8
1.6
11.0
0.2
0
0.1
-
Micryphantidae
0
1.0
1.0
5
- Theridiidae
2.6
0.5
6 - Agelenidae
7
-
Dictynidae
8 - Salticidae
9 - Thomisidae*
i
l -
Pi
sauri dae
Augus
0.7
0.7
0
4
sweeps
0
1.2
0.2
3.1
to
3.0
0
0.2
0.2
0
0.2
2.2
2.4
2.4
4.8
5.8
10.4
1.6
7.4
I
'1.2
1.2
3.0
3.4
16.6
3.0
30.2
2.0
0.4
0.2
5.0
30. 6
16.8
0.6
0.2
0.8
6.2
6.6
0.2
6.4
0
6.6
2
-
Cl ubi oni dae
0.2
0.2
1.0
'13
-
Lycosidae
0
0.2
0
0..l
?.4
7.2
I
10.0
5L. ö
a
8.2
6.2
L
18. 2
59. 0
68.4
5.2
73.6
I
Unidentified spiders
Total
* + I adult
specimen
of
Philodromidae (10)
in
June
t
-36-
Table
l6.
of the spider fauna in the vegetation zone of
the dry meadow A2 in summer'1979. The numbers in parentheses behind
the names correspond with the family-numbers in Table ]5. The composition was investigated by means of sweep net collections. Only
the adult spiders ar"e listed in the table.
Species composition
Spider species
Aculepeira ceropegia (l
Araniel
la cucurbitina
)
6
(1 )
0
(l)
(l)
(l)
4l9i9p9 bruennichi
il
Mangora acalypha
J
Meta segmentata
0
Tetragnatha pinicola (2)
Linyphia triangularis (3)
Linyphia spec. (3)
Meioneta
rurestris
Hylyphantes
(3)
nigritus
E
0
0
0
(4)
Theridion boesenbergi (5)
Theridion impressum (5)
Enoplognatha ovata (5)
Neottiura bimaculata (5)
Evarcha arcuata (8)
Heliophanus flavipes (8)
'|
0
'I
4
23
9
Xysticus cristatus (9)
Xysticus kochi (9)
25
Philodromus rufus (10)
I
Pisaura
mirabilis
Pardosa pul
lata
(11)
(13)
Pardosa amentata (.l3)
Total
I
2
I
I
106
00
0t
n
00
0
00
0
00
4
00
0
02
0
t0
0
t0
5
41
0
00
00
0
t4
2
0l
22
8
6020
3210
0000
0000
5100
1000
0000
0
0
n
I
0
I
0
1
0
0
0
U
0
I
49
3l
5
I
0
13
t8
6
I
I
3
I
19
3
I
1
23
I
I
21
7
84
17
31
1
'I
2.56
0.43
0.43
i.28
0.43
8.12
1.28
0.43
0.43
9.83
0.43
0.43
8.97
2.99
35.90
7.26
13.25
0.43
0. 43
B
2
'I
26
22
234
3.42
0.85
0. 43
I
00.0
-37
Table 17. Number of families, number
and evenness(see Methods,
spiders
in the vegetation
of species, diversity,
2.3.6.) of the adult
zone
of
two abandoned
grassland biotopes (investigated by means
sweep
net data of Tables 12 and 16). The
of
the
two
diversity values are significantly different
(t-test,
P <0.05).
Megaphorbe meadow
Number
of families
Number
of
Diversity
species
S
H'
Evenness E
-
H'llnS
Dry
meadow
At
A?
l0
l0
23
22
I .85
2.14
0. 59
0.69
-38of the total of spiders capturedin Al and A2 results in
an "overlap index" C.ip of 0.32 (see 2.3.10)' Thus, the spider communities in the two abanäoned grassland biotopes differ widely.
The comparison
More extensive
studies in other
labyrinthica (Cl. ),
DdiomecieiF'imbrigtus
3.1.3.
abandoned gr"ass'land
of Zurich resulted in the additional
surroundings
locations in the
species Agelena
Hyposinga :qnguinea (C'1. Koch) ' l'49!s mengei (B1ackw. ) '
L. and Hel iophanus auratus C-1. Koch.
Seasonal change
of
abundance and
daily activity
of abundance
l5 show the spiders'seasonal trends. Adult stages of
T. extensa. T. oinicola. H. niqritus, N. bimaculata' E. ovata'
H. flavipes, P. nirabilis, and X. cristalus were tound malnly rn June'
lnrnatureEages-mosQ-between July and September. 0f E' arcuata adult
stages could be found relatively oiten from June to Se!-tem-bET-and
imature stages in August/September. The contrary was true for
L. triangularis, A. gracilens, M. s-egmentata, A' qugdra!us: ang- Ä. Iiuen;ftFl-inunature-sTagäs were caugtrt by sweeping in June/July'
3.1.3.1.
Tables
Seasonal change
ll
and
;äuIT sTages-not before August/September.
Table 18 represents the relative density of the spiders (= number of spiders/I00 sweeps) as a function of the season. The table shows similar
trends for the two locations Al and A2. In all the seasons' more ißnature than adult spiders were captured. Considering the total spider
density (inmature + adult stages), a strong increase in the spider
density irom spring to late summer can be noticed. The adult spiders
reached their rnaximal density in June, the minimal density in August'
0n the contrary, the minimal density of the'irunature spiders occurred
in June, the mäximal density in August. The females of several spider
species of the locations studied probably laid their egg sacs in
spring and died soon thereafter. The spiderlings then hatched in the
coursÄ of the summer. Since abandoned grasslands are spared to a large
extent from human influences all year long, the spiders can live there
undisturbed and catch their prey fr"om spring to autumn (about 6-7
months/year).
3.'l.3.2. Daily activitY
Table
in
l9 gives informations
on the
daily activity of the spiders living
abandoned grasslands.
Most orb-weaving spiders were observed feeding by day and by-nig-ht {e'g'
A. bruennichi, lable 20). They are both diurnal and nocturnal' 0f the
or5:weavlng spider Nuctenea cornuta (Cl.), only the inmature stages are
occasionaliy äctive-IuFä!-tfiä-aay, vthereas the adult stages of this
species are nocturnal* (NYFFELER & BENZ, 1980b; NYFFELER' l98l).
in abandoned grasslands belonging to the
fami I ies Agelenidae, L.inyphi idae, Mi cryphantidae, Theridi idae' and
Dictynidae were observed feeding during daytimes in most cases' In the
webs-, however, the remains of nocturnal prey species were found, too'
Thesi spiders are therefore both diurnal and nocturnal '
The web-building spiders studied
It
happens
observed
very rarely that an adult specimen of N. cornuta can
orb-web during the daylight hoursl--
in its
be
o
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!
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6
f
a
5
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cl
dl
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ol
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ooooo
d;
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46
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f
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60
-40-
Table
.l9.
Daily rhythm of activity of the spiders in abandoned lands
in cultivated meadows (direct observations in the
and
field
and supplementary informatjons from literature).
Spider group
Type
of activity
0rb-weaving spiders:
Aranei dae
A, ceropegia
A. diadematus
A.-SFuenniT6'Tcucurbitina
Ä.
M. acalypha
M. segmentata
A. quadratus
N, cornuta
Tetragnath i dae
Tetragnatha spp.
Pachygnatha spp.
diurnal and nocturnal
diurnal
and nocturnal
diurnal and nocturnal
diurnal
diurnal
diurnal
and nocturna'l
and nocturnal
and nocturnal
(diurnal ) and nocturnal
mainly nocturnal
diurnal
diurnal
and nocturnal
and nocturnalä
Space web spiders:
Agel eni dae
Agelena spp.
Li nyphi i dae
L. triangularis
div. species
Mi
cryphanti dae
Theri di i dae
E. ovata
fl-ltFT6ssum
N. bimaculata
Di
ctyn i dae
div.
species
diurnal and nocturnal
diurnal and nocturnal
diurnal and noctunnal
diurnal and nocturnal
diurnal and nocturnal
diurnal and nocturnal
diurnal and nocturnal
Hunting spiders:
Salticidae
E. arcuata
d i
di unnal
Thomi s i dae
H'l-TiEipäs
Xysticus spp.
Phi I odr"omidae
Phi lodromus spp.
diurnalc
Pi sauri dae
P. mirabilis
di urnal c
Lycos i dae
Pardosa spp.
d'iurnal
Cl ub i oni dae
Clubiona spp.
nocturnal
urnal
diurnalb and nocturnal
a
a
After informations from literature, adult stages are hunters
b
Mainly diurnal
c
It
has not been observed
if also
nocturnal
-4]
Iable 20. Daily rhythm of feeding activity in Argiope
bruennichi in the vegetation zone of the
abandoned
Dayti
me
land biotope A3
4. 8. I 976
10.00
.00
50.00
I I .00
40 .00
12.00
50 .00
10
'I
60. 00
so. oo
I spiders feeding:
15.38
N
=
17
4l.18
4t.18
30.77
47 .06
30.77
35.29
38.46
35. 29
I5. 38
17.00
i 8.00
13
38. 46
15.00
16.00
=
6.8.1976
38. 46
3.00
14.00
sunrner 1976.
Date
5.8.1976
N
9.00
in
60 .00
23
.08
20.00
2s.41
24.00
35.29
-42Hunting spiders of the families Salticidae, Philodromidae, Pisauridae
and Lycosidae (genus Pardosa) were observed hunting during the day.
Whether they hunt also at night, could not be ascertained. Thomisidae
(genus Xysticus) could be observed feeding mostly during the day, less
often at night. The Clubionidae (genus Clubiona) are hiding in a sjlken
tube within a leaf during the daytime and hunt at night.
The observations show that in both abandoned grassland biotopes diurnal
as well as nocturnal spiders are present, indicating that the predatory
pressure of the spiders on the insects of these biotopes is exerted day
and night.
3.1.4. Spatial distribution of spiders
3.1.4.1. Vertical distribution of spiders
of
In Table 21, the vertical distribution of five species
.l979.
orb-weaving
represented for September
The table
shows that orb-webs are found from directly above the ground
(A. bruennichi, M. segmentata) up to the top of the vegetation zone
(A. diadematus, N. cornuta).
spiders
in location Al is
The weighted average (i*) is an estimate of the vertical distribution of
the web sites of the whole orb-weaving spider guild in the open grass
area of biotope Al. The population densities of Table 22were used as
weighing factors for the calculation of i*. The distribution of i* shows
that in 7l% of all orb-weaving spiders the orb hub was placed at a
height of 50-100 cm above ground. This means that in the open grass area
the orb-weaving spiders exert the strongest predatony pressure on insect
populations at a height of 50-100 cm. At heightsofless than 25 cm and
more than l25 cn above ground, the predatory pressure exerted by orbweaving spiders was negligible.
In Fig. 3, the vertical distributjon of the orb-weaving spiders
A. bruennichi, A. quadratus and N. cornuta in location Al in the summer
of-Tmf s reprEsEnTed gr'aphically. A statistical analys js of the data
shown in the figure produced significant differences in the mean values
of A. bruennichi, A. quadratus, and N. cornvta from July to September
(Mann-üIilneyn:te.f, p <0.01). The mean values of A. quadratus and
N. cornuta showed significant differences only in July and August
Tp_Zö.oTl; but not in September (p >0'05). These values indicate that
different spider species exert their predatory pressure on insect
popu'lations at different heights above ground.
The vertical segregation of the prey catch'ing areas of sp'iders can have
prey selection as a consequence. This could be observed in orb-weavjng
spiders mainly: A. bruennichi builds its webs near the ground (orb hub at
about 0.3 m above ground). For this reason, A. bruennjchi captures many
grasshoppers
in
grasslands abounding
in
gr"asshoppers. A._quadratus and
m above ground on the
grasslands abounding in grasshoppers' only a few
A. diadematus build their webs at more than 0.5
averase.-m;, even in
gnasshoppers
are caught by A. quadratus and A. diadematus (<0.5% of their
food ) .
3.1.4.2. Horizontal distribution of sp'iders
among different habitats
Table 22 shows the horizontal distribution of six orb-weaving spider
Horizontal distribution
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Distance from
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O.5m*
Argiope
bruennichi
Ju
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August
ilonth
September
Vertical distribution of three orb-weaving spiders in the megaphorbe neadow Al in opfikon near Zurich (July to September 1979).
li,lean
value
t I
webs observed.
SE, numbers
in the graphic indicate the no. of
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-46species among different habitats within location A1 (September 1979).
table
sholvs
The
a heterogenous horizontal distribution of the six spider
species.
0f the spiders of the
open grass area, A. quadratus, and to some extent
N. cornuta and T. extensa are the most inportant insect predators; on the
ililli-aes, on thtoTfier -hand, A. bruennichi and to some extent A. quadratus
are important, whereas in the-llru6s är-ound the open grassland,@a91
and
A. diadematus predominate.
Horizontal distribution within g habitat
Tables 23-24 shol'r the index of Morisita of the spiders in the locations Al
and A2 for two observation data. The values indicate that within the
vegetation zone of the two abandoned grassland biotopes, the horizontal
distribution of the spiders represented a random distribution (lp not
significantly different from l; p >0.05) or a slightly aggregateö distribution
(16 significantly larger than l; p <0.05). From these spider distributions,
a coresponding distribution of the spiders' predatory pressure on the
insect populations can be derived,
3.1.5. Prey capture of spiders
3.1.5. 1. Hunting strategies
The hunting strategies which the spiders Iiving in abandoned grasslands are
equipped with are manifold. In Table 25, the quantitative composition
of the hunting strategies used by the foliage-dwelling spiders of both
locations Al and A2 are represented. The table sho'rs that in the
relatively moist location Al the greater part of the spiders catch their
prey with orb-webs, while in the dry grassland of location A2 most
spiders hunt their prey without webs. The average web areas of the
oib-weaving spiders living in location Al anrounied to t60-640 cm2 in
August/September (Table 26).
3,1.5.2, Prey
composition
Orb-weaving spiders
observations in 1976 - Tabie 27 represents a comparative compilation of the
prey composlTTons-öF adult females of A. bruennichi and A. quadratus in the
four locations A3, A4, A6, and A7. ConEiGiTn!'Tfr-nunrbeF-öT-EäFTured prey,
the food of A. bruennichi and A. quadratus consisted essentially of small
Di ptera. RegäidTng TfiE-6Tomass;-T6Elley-Tf A. bruenni chi was mai nly
of grasshoppers in two locations and predominantly of honey-bees
two other locations, In the biomass of A. quadratus, the bees predominated,
too.
composed
in
in 1978 - During the sunnner of 1978, an A. bruennichi population
;SserGAl;-i ocati on A8. Grasshoppers ( about 20%,-EETeFü@irppgq
paralleius (Zett.)), cicadas (about 20%, mainly Cicadella vjridis (1.) and
Diptera (about 40%) were predominant in the prey composition of this
Observations
was
A. bruennichi population.
in 'l979 - Tabies 28-31 give a compilation of the prey compositions
orb-weaving spider guild on the megaphorbe meadow Al. Diptera and
Homoptera (cicadas, aphids) were the most important food components of this
orb-weaving spider 9uild. Relatively often A. bruennichi, A. quadratus, and
Obsenvations
of the
Total spiders
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-52-
of three araneid species in the megaphorbe meadow
1979. s = small, m/l = medium to large species.
Table 28. Prey compositions
Al in
summer
Araneus quadratus
July
Prey
s
m/l
Apterous ants
Bees
Diptera
Diptera
88.24
0
0
0
sa
Other Hymenopt. m/l
Winged aphids
Apterous aphids
Ci cadas
Thysanoptera
Heteroptera
Grasshoppersb
Lepidoptera
Trjchoptera
Chrysopi dae
Scorpi onfl i es
Col eoptera
Ephemeroptera
Sal ti ci dae
Other spiders
Unidentified prey
0ther Hymenopt.
0.65
0
4.58
0
0
0
0
o
1.3.l
0
0. 65
0
1
.31
0
0
0
3.27
153
items
No. webs
7
No. observation days I
No. prey
a Winged individuals
b One adult specimen
of
A.
di
adematus Arg.
Aug. Sept.
Aug.
Sept.
75.42
70.00
57.06
60. 58
l 84
0.14
0. 99
7 .49
0.42
L84
00
9.04
0.42
0. l4
00
0
00
00
00
0.99
0.28
00
0.14
0.85
0.88
2.19
.32
1.80
0.28
0.69
8.25
13.71
708
47
34
0
1
0.35
6.23
I
9.47
0.6]
0. 09
0.09
0.61
0.09
0
2.02
il40
59
Roeseliana roeselj (Hgb.)
1.52
3.02
00
6. 51
0.14
1.25
00
0.55
0.14
00
0.28
1 .25
00
00
0.14
I .66
722
129
6l
0
0.73
t8.25
0
0
6
.57
0
bruenni chi
Aug.
Sept.
44.67
68.25
5.27 0.40
0.54 0.40
4.63 0
7 .94
5. 06
3.55 0.79
4.52 ll.sl
0.32 0
24.76 6.35
2.05 0 40
0.11 0
0.22 0
0.40
0
00
00
o.il 0
0.97 r . 59
0.32 0
o.il 0
0.22 0.40
2.s8 1.59
.
0.73
0
0
0
0. 73
0
2.92
137
Ir
929
95
52
252
24
-53-
Table 29. Prey composition of Nuctenea cornuta
A1 (spring/summer 1979).
Prey
Small Diptera
Itledi um/ I arge Di
ptera
in the
megaphorbe meadow
May
June
July
82. 98
75. 40
80. 78
l7
August
85. 05
2.84
0
0.
Small winged Hynenoptera
0
0.49
0.17
I .87
Bees
0
0
0.09
0
}Jinged aphids
10.64
ci cadas
0.71
Thysanoptera
0
Lepi doptera
4.21
.l6
12.17
0
8.4l
0.09
0
0.65
0. 70
3.74
0
0.16
0. 35
0
Tri choptera
0
12.46
l.9r
0. 93
Ephemeroptera
0
0
0. 96
0
0. 7l
4. 05
I .13
0
Tetragnatha spec.
n
0
0. 09
0
Unidentified prey
1 -42
2.43
I .39
0
No. prey items
l4l
618
l l50
107
zo
47
64
1l
J
5
6
2
Co l
eoptena
No. webs
No. observation days
.7t
0.
-54-
Table 30. Prey composition
gaphorbe meadow
of Meta segmentata in the
Al (sumrner 1979).
August
Prey
September
hh
Small Diptera
?7 .39
39. 34
14.23
5. 46
Small winged Hymenoptera
4.25
2.73
arge Hymenoptera
0. 64
0
Medium/1
Medi um/
1
arge Diptera
Apterous ants
1.27
I'li nged aph ids
15.92
Apterous aphids
Ci cadas
0.42
31 .2'l
0
.l8.58
0
31 .15
Thysanoptera
0.42
0
Tri choptera
0.42
0
Ephemeroptera
I .49
0. 55
Unidentified prey
2.34
2.19
No. prey items
471
t83
No. webs
309
75
7
3
No. observation days
me-
-55-
Iable 31. Prey composition of Tetragnatha extensa in the
phorbe meadow
Prey
Smal
I
Diptera
Medium/large Diptera
Sma11 winged Hymenoptera
l,Ji
nged
Al
(
spri nglsummer
une
July
l8
57. 50
J
88.77
82.
1.09
0. 83
0
'I
0
mega-
979 ) .
May
3.62
aph i ds
1
.21
0. 83
4. 53
15.83
Ci cadas
3.62
I .51
Thysanoptera
0
0.60
Tri choptera
0
4. 83
Ephemeroptera
0. 36
0
0
Chrysopi dae
0
0. 30
0
0.72
I .81
0
Tetragnatha spec.
0. 36
0
0. 83
prey
I .45
3.02
0
No. prey items
276
JJ
120
No.
138
'156
Col
eoptera
Unidentified
webs
No. observation days
J
I
E
0
0
24.17
53
q
-56A. diadematus captured
Hymenoptera as
well. Temporarily, N. cornuta and
T. extensa captured Trichoptera quite often, In this location,
the
$r_lfCgnnfgli population captured almost no grasshoppers (only in one web
oneTZuIT-Emale of Roeseliana roeseli (Hgb.) was found), The captured
were cicadäi-{9E7@i6cläils maior (Kbm.)) and winged aphids
Homopter"a
(mostly Anoecia corni) (Tables 32-33).
Space web spiders
The prey compositions of funnel web spiders are compiled in Table 34
(locations A3 and A5; observation years I976-1977) and Table 35 (location
A1, June/July 1979). Table 34 indicates that the prey composition of
A. labyrinthica varies. In location A3, the prey composition of
the
funnel web spiders consisted mainly of ants, Apidae, Trichoptera, Lepidoptera
and Diptera; in location A5, the food of the funnel web spiders was largely
composed of orthoptera, Lepidoptera and Diptera. In the prey composition of
A. gnacilens in location AI beetles and cicadas predominated in June,
whereas Trichoptera (75%) prevailed in Juiy (Table 35). In other locations,
remains of cicadas and beetles in quite large numbers have been found in
the webs of funnel web spiders.
Spiderswith space webs belonging to other families were only cursorily
observed. Linyphiidae (1. triangularis) were often observed capturing Diptera
and Homoptera (aphids, cicadas) in abandoned grasslands. 0f Theridiidae
(Theridion irnpressun L. Koch, E. ovata), only a few data on the prey compositions could be gather"ed in abandoned grasslands. Their prey compositions
seem
to
be quite heterogenous (fron small
to large insects,
and
flying
and
running insects as well). In abandoned grasslands, Dictynidae could mostly
be observed as predators of Diptena.
Hunting spiders
llith
to hunting spiders in abandoned grasslands, quantitative analyses
only for crab spiders. In 1976, it was observed that they captured
mainly Diptera (about 80% of their" food). In 1977-1979, Xysticus sp. were
also observed consuming Diptera, but ants and bees as well.
regard
were made
3.1.5.3. Prey capture rates
Estimate
of the prey capture rate of
an A. bruennichi population
Table 36 shors hou many insects of medium to large size were captured on the
average by females of A. bruennichi in location A3 on three observation days
at the beginning of August 1976. As the table indicates, a female of A.
bruennichi caught on the average one larger insect/day,61% being bees and
10% grasshoppers. Small flying insects (dipterans, aphids) have not been
taken into consideration in this census. If the small flying insects had been
counted, too, the capture rate would be several times as high (see Table 37).
Estimate of the prey capture rate of an orb-weaving spiden guild
Table 37 shows, how many insects on the average were counted per web of three
orb-weaving spider species in location Al. These figures do not represent the
exact capture rate, but are a slight underestirnate of it (see 2.3.8.1.,
nethod 2). However, the values impart an impression of how many insects are
filtered out of the aerial plankton by one web per day on the average. The
table shows that the average capture rate of N. cornuta equalled more than
l8 prey organismsfweb/day. This means that from 200 up to over 400 insects
were caught per mz of web area per day.
-57-
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Table 37. Prey capture rate (no. prey items/web/day) of three orb-weaving spider species in the megaphorbe meadow A1 (study year 1979). l^ihen not
otherwise stated three days of observationi exceptions as numbers in
parentheses.
Prey/web/day
tenea
cornu ta
Sa i son
Nuc
May
>5
June
>]8
July
>]8
>21
t
Argjope
bruenni chi
(td)
>14
>ro (5d)
>20
>10 (1d)
August
>3'l 5
>204 (5d)
September
>408
>193
Augus
September
Preylrr,2 web/daya
Araneus
quadratus
(ld)
a Calculated from the data of Table 26; from May to July the diameters of
webs
were not measured
concerning food.0bservations in six orb-weaving
megaphorbe meadow Al (spring/summer 1979). The
values were calculated from the data of Tables 28-31.
Table 38, Niche breadth
(Bi)
spider species in the
T.
extensa
N.
A. quadratus
A. diadematus
A. bruennichi
cornuta
M. segmentata
May
Niche
June
breadth
July
1.26
1.47
2.41
0.72
I .70
I .50
B;
August
September
1.37
I .71
I .96
2.73
2.46
3.66
2.04
4.53
3.44
-62Maxjmum
pl aced
prey capture rates
in
orb-webs which were
particularly well
of Tables 36 and 37 represent the average of well and badly
In a few particularly well exposed orb-webs, a much higher
number of insects could be counted; in the web of an A. bruennichi, for
instance, 7 grasshoppers at one time, in another web 4fTIcääElThe values
placed webs.
occasionally, more than 100 Diptera could be counted per web of
N. cornuta. These observations indicate that large orb-weaving spiders
have a high killing potential.
Niche breadth and niche overl
concern
r
food of web-buildi
spl ders
The niche breadths concerning food of six orb-weaving spiders are compiled in Table 38. They were calculated on the basis of method ?.3.9.,
using the data of Tables 28-31. The niche breadth of N. cornuta proved
to be the smallest (Bi = 0.72-t.70), the one of l:_:egmsn!l!g
(Bi = 3.44-4.S3) was the largest.
llith the data of Tables 28-3i and 35, the overlaps of the prey compositions of web-building spiders in location Al were also calculated. The
overlap^values el are shown in Table 39.0f the 23 tested pairs 20 (87%)
have a Cl of nore than 0.60. This indicates that the prey compositions
of the various orb-weaving spiders overlap rather strongly.* 0n the
other hand, the prey compositions of orb-weaving spiders and funnel web
spiders show only small over'laps (CÄ <0,'l0). Therefore, orb-weaving
spiders and funnel web spiders complement each other in thejr function
as insect predators.
ders as predators of pest i nsects
In abandoned grasslands, aphids form an important component in the food
of web-building spiders. The species composition of the aphids captured
by orb-weaving spiders in Al is compiled in Table 33' The table shows
that, among others' the spiders caught aphid species which can be agricultural pÄsts, e.g. Rhopalosiphum padi 1., Sitobion aYenae-F.'AE!'']t
fabae Scop., Hyaloptef[llunT-GEofTF- and Myzus persicae Sulz' This
3. I
.7.
Spi
Jill?ates tnafllTEä-destroy pest insects in
abandoned grasslands'
3.1.8. Soiders as oredators of beneficial insects
As the prey compositions (Tables 27-35) indicate, the spiders feed not
only on pelt and neutral insects' but also on beneficial insects as
honäy-bees, Coccinell idae, Chrysopidae, and.Syrphidae' Whether one or
the äther group dominates' depends on the biotope and its biocenose'
Therefore, the same spiden species, which is a predator of neutral or
pest inseits in one biotope, can be a predator of benefjcial insects in
ly in
another biotope. This phenomenon could be observed especial
'l976'
an
A. bruennichi and A' labyrinthica. In the biotope A3 in
Ä:-FuennTA'I populäTJon-Eä-El-the most part on honey-bees' another
If the overlap
at species level of the prey instead
values would possibly have resulted'
had been calculated
of order levei, lower overlap
-63-
Table 39. 0ver'lap
of prey composition of six
orb-weaving
spider species and one funnel web spider species
(niche over'lap Ö.f;
spring/summer
,l979.
in tne
megaphorbe meadow
the data of Tables 28-31 and
Species pairs
T.
extensa
T.
extensa
quädra tus
N. cotnm
Al
N. cornuta
ÄlquäZl[Tus
Al in
The values were calculated from
35.
Niche overlap el
May
June July
0.99
0.99
August
September
0.90
0.86
0.99
0.98
A. bruennichi
N. cor"rxrta
0.77
Ä.luäAraif
A. bruennichi
0.85
l
00
A. bruennichi
A.-?TäAedErs
0.89
0
.97
A.
0.88
0.80
0.95
0
fr.
bruenni chi
;esmänTeTä
A. quadratus
A. diadematus
.97
0.91
N. cornuta
t'l.=eEfrö;Tata
o.52
A.
M. segmentata
0.61
0.80
A. diadematus
fr-esmeniäE.
0.70
0,76
quadratus
A. gracilens
N. cornuta
0.
A. graciiens
A. quadratus
0.07
l0
-64one
in the biotope A4, at a distance of 2
km, mainly on grasshoppers
27). Likewise, an A. labyrinthica population in location A3 fed
largely on bees, but in location A5, at a distance of I km, mainly on
(Tab1e
grasshoppers (Tab1e 34).
3.1.9. Predator-prey relations between spiders and adult lepidopterans
e! al. (1964) state that: "Moths, by virtue of the loose scales
that cover their wings and bodies, are admirably adapted to elude
capture by orb-weaving spiders. Rather than sticking to the web, they
may simply lose some of their scales to the viscid threads, and then fly
on". In the course of the present investigations one could actually
observe rather often that Lepidoptera, having flown into spider webs,
tear themselves away from the webs, thereby losing some scales, and fly
on (NYFFELER & BENZ, l98lb). Thatthe anti-predator mechanism found by
EISNER et al. plays an important role for Lepidoptera in the field, is
corroborated by the fact that Lep'idoptera form only a small component
EISNER
of the total food of the orb-weaving spider species studied (<l%, see
Tables 28-3.l). A possible connection between EISNER's anti-predaton
mechanism and the predatory behaviour of A. bruennichi has been
reported by NYFFELER & BENZ (1982a).
3.1
.'l0.
3.1.10.'l. Prey kjlling rate of an A. bruennichi population
,
Table 36 shows that in the beginning of August 1976 abgut 0..l8 bees/m'/
day 1- 1996 bees/halday) and about 0,03 grasshoppers/nz/day (= 300 grasshoppers/ha/day) were killed by this A. bruennichi population. Assuming
constant weather condjtions during 30 days, this would amount to a
capture rate of 54'000 bees (about 5 bee colonies) and 9'000 grasshoppers/
ha/month.
3.1.10.2. Prey killing rate of an orb-weaving spider gujld
The question of the spiders' importance within an ecosystem is closely
related to the question of their prey killing rate. This rate can be
estjmated most easily for web-building spiders and among those most
easily for orb-weaving spiders. The quantity of insects which is daily
filtered out of the aerial plankton by orb-weaving spiders in the
vegetation zone of abandoned grassland biotopes necessarily depends on
the total area AO of the webs of all spiders livingin a biotope, i.e.
n
A=sA.
pz-r
i=l
where
A. is the
'I
web area
of spider i.
filters the aerial
of simplicity, thjs model
was limited to the orb-weaving spider guild of the bjotope Al. In order
to have a piain area relation, the nunber of insects caught by the
spjders per ha and day was estimated. For this purposet two preliminary
questions had to be answered:
This web area is built
plankton in the vegetation zone. For the sake
on each fair-weather day and
-65-
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-66(l) How large ig the web arqa built by orb-weaving spiders per unit
ground area (cmz web area/nz ground area)? - Knowing the web densities
(Tab1e 22) and web areas (Table 26), the average web area/ground area
was calculated. The values for September 1979 are compiled in Table 40a.
(2) Hqw many insects in the vegetation zone fly on the average through
one m4 of web area and are entangled in it per day? - Table 37 shows
that in September'1979, more than 408 insectsfmz web area of
A. quadratus webs and more than I93 insects/m2 area of A. bruennichi
we6iliäFitTittered out of the aerial plankton.
From the data established in points I and 2, the prey killing rate P'
'i.e. the number of prey insects/m2 ground area/day' was calculated by
means of the formula
P=A.N
where A
is the
web area
in
cm27m2 ground
area and N the number of
captured insects/mZ web arealday. The capture rate established for
A. quadratus (>408 insects/mz web area) was also used for the species
Ä. diädeinafus, N. cornuta, M. segmentatat, and T' extensa.
in Table 40b show how many insects, at least' were
destroyed by orb-weaving spiders per mz per day in the biotope Al in
September 1979. They amounted to respectively 27 or 48 insects/mzlday in
the open grass area and respectively 19 or 5l insects/m'lday on its
borders (wayside). In the shrubbery, at least 45 insects/mzlday were
The P-values compiled
killed by orb-weaving-spiders. The prey killing rate thus varied between
at least l9 insects/mZlday and 5l insects/mzlday (mean value: >38 insects/
n2/day). Supposing that this orb-weaving spider guild is active during
100 days per year, it would destroy more than 38 million insects/ha/year.
If, on the basis of the prey compositions (Tables 28-31)' an average
fresh weight of 4 mg/insect is assumed, a biomass of more than 150 kg/ha
of insectfreshweight would be killed each year. This is merely the prey
killing rate of thÄ orb-weaving spider guild. The spider cormunity of
the biotope Al contained however various space web spiders and hunting
spiders as welL The pr"ey killing rate of the whole spider commun'ity is
therefore significantly higher than 150 kg fresh weight/ha/year.
3.,l.10.3. Energy flow through spider conmunities
A conversion (2.3.1.l.1.) of the prey biomass values of section 3.1'10.2'
results in an'energy flow 1= prey kil1ed) through the orb-weaving spider
guild of the biotope Al in the order of nore than 900 MJ/ha/year.
3.2- The role of soiders as insect predators in cultivated meadows
Cultivated meadows are chanacterized by the fact, that their vegetation
zone is mown 3-4 times per year. The cultivated grasslands investigated
'in this study are per,rnanent meadows. They represent a mjxture of
numerous flowering plants (grasses, legumes, herbs). As Iignified plants
are largely absent, the vegetation in cultivated meadows is more elastic
than in abändoned grasslands and thus facil'itates the sweeping method'
Through mowing the vegetation zone is removed, j.e. the living space of
many ipiders is destroyed; it regrows in the followjng weeks. The
locätiäns of the cultivated meadows studied are comp'iled in Table 8. In
contrast to the investigations in abandoned grasslands, the studies'in
-67cultivated
meadows
spider communities
included also the spiders on the ground surface.
of the vegetation
and
of the ground surface
3.
1
1= ground
differed in their composition.
2
.
.
The i nfl uence
of
The
zone (= foliage-dwelling spiders)
dwelling spiders) distinctly
mowi ng
periodic destruction of the living space and the egg sacs through
mowing is an extreme stress for the spider populatjons of the vegetation
zone. The total spider density in the vegetation zone diminishes
drastically after mowing. The example listed in Table 4l shows that
after mowing, the total spider density of the vegetation zone of a
meadow had decreased by 50%. Similar effects could be observed in other
cultivated meadows. As a consequence of these periodic stress situations'
the densities of the foliage-dwelling spiders in cultivated meadows are
extremely low (1.5 spiders/mz, in Table 4l ).
As the values in Tab.le 42 indicate, mowing has a negative effect on
ground-dwel1ing spiders, too. Compared to the vegetation zone, the
spider densities^on the ground surface are nevertheless relativeiy high
The
(16-42 spiders/62, Table 43).
3.2.2. Spider
communities
of cultivated
3.2.2.1. Spiders of the vegetation
meadows
zone
family and species composition of the foliage-dwel1ing spiders in
five cultivated meadows were investigated by means of sweep net samples.
Tables 44-48 show the family composition of the imrnature and adult
spiders in these meadows. Spiders of the eight families Araneidae,
The
Tetragnathi dae, Li nyph i i dae, Mi cryphanti dae, Theridi i dae, Sal ti ci dae,
Thomjsidae, and Lycosidae predominated in the sweep-net samples (>85% of
the immature and adult spiders). More than 50% of the captured adult
spiders were females,
The species composition
of the adult spiders in the five
meadows
js
Tables 49-51. Adult stages of the familjes Thomjsidae
(X. cristatus, L__!ggll, Tetragnathidae (T. pinicola, Pachygnatha
degeEii Sundevall), Theridiidae (E. ovata primari'ly) and Araneidae
(moitty Mangora CgelJllg (l,la]ck.)) were the ones most frequently
captured with the sweep net.
represented
in
In cultivated meadows, adult Salticidae were found only in very low
densities. Also A. bruennichi and A. quadratus, the orb-weaving spider
spec'ies rather frequEnT-ä'T6andonEä gras;TanAs, were seldom located
in cultivated meadows (as immature stages).
The foliage-dwe11ing spiders in cultivated meadows were for the most part
species whose adult stages are medium-sized (see Table l3)'
A. ceropegia is the largest spider found in cultivated meadows around
Zuri
ch .
3.2.2.2. Spiders of the ground surface
The family and species composition of the ground-dwelling spiders living
in the cultivated meadow C3 was investigated by means of pitfall traps.
-68-
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-70-
Table 43. Density of the gr"ound-dwelling web-building spiders
vated meadows near Zurich (June/July 1979).
Number of
s quares
Date
Meadow
Vegetati
hei
on
ght
in
Spi ders/m2
'13.6.1979
804
26.7 .1979
404
l5-.l8 cm
4-8cm
c5
27
.6.1979
20p
very short
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c5
26.7 .1979
404
50
18.13
m
cm
42.50
15.94
b Square of 0.4 m x 0.4 n
of the spider fauna in the vegetaof the cultivated meadow Cl (spring 1979).
composition was investigated by means of sweep net
tion
zone
collections. Imnature
and
adult spiders
were counted'
23.5.
5.6.
Total
N=122
N= 46
N=l 68
Aranei dae
28.69
34. 78
30.36
Tetragnathi dae
30.33
17.39
26,79
.47
15.22
19.64
8. 20
19. 57
Spi
der
fami
'ly
Composition
in
%:
Thomi s i dae
Theri di i dae
Mi
cryphanti dae
17
2.46
10.87
'l
I .31
4.76
Phi I odromi dae
4.
0
2.98
Li nyphi i dae
0
2.17
0.60
2.46
0
1.79
Di
ctyn.idae
Unidentified spiders
Total
mown
21.88
Table 44. Family composition
The
culti-
unmown
cl
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a Square of 0.2 m x 0.2
two
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1
2.46
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-73-
of the spider fauna in the vegetatjon
meadow Cl (spring 1979). The compoof
the
cultivated
zone
sitjon was investigated by means of sweep net collections.
Table 49. Species composjt.ion
0nly the adult spiders were counted.
23.5.
Spider species
Aculepeira ceropegia
2
5.6.
0
2
4.76
7
8
19.05
,l
Mangora acalypha
Total
Tetragnatha montana
U
I
I
2.38
Tetragnatha obtusa
0
I
I
2.38
Bathyphantes graci l is
0
I
I
2.38
Eri gone denti pal pi
I
0
I
Tiso
s
vagans
5
2
2.38
il
.90
Neotti ura bimacul ata
0
I
I
2.38
Theridion spec.a
0
I
I
2.38
Dictyna uncinata
I
0
I
2.38
Lathys humilis
2
0
2
4.76
t0
6
t6
38.10
I
2
4.76
22
42
Xysti cus cri status
Xyst'icus kochi
Total
a Palpus was lost
.l
20
100.0
-74-
Table 50. Species composition of the spider fauna in the vegetation zone
of the cul ti vated meadow C4 ( sunrner 1 979 ) ( otherwi se as Tabl e 49 ) '
?9.6.
Spider species
Arani el
l
a opi sthographa
I
12.7.
0
9:3:
0
Totar
1.59
I
Tetragnatha pinicola
?
I
0
2
4.76
Pachygnatha degeeri
I
0
32
33
52. 38
Microlinyphia pusilla
0
0
I
1
l
59
'I
.59
I .59
Meioneta rurestris
0
0
I
I
oedothorax fuscus
I
0
0
I
Theridion impressum
2
0
0
2
3.17
Enoplognatha ovata
2
0
6
8
12.70
Neott'iura bimaculata
I
0
I
2
3.
I
U
0
I
1.59
0
I
0
I
1
.59
5
0
0
5
7
.94
I
I
AO
Di
ctyna Plgllsa
Hel
iophanus fl avi
Pes
Xysticus cristatus
l7
Xysti cus kochi
I
0
n
Philodromus cespitum
Phi lodromus rufus
I
0
U
1
.59
0
n
1
r .59
n
'I
I
1.59
Pardosa
I
palustris
0
l9
Tota l
a This species
is
new
for the
Swiss fauna
42
'I
63
100.0
-75I
E
c
N
O
!
c
a
o
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rO
3o6
!p
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OF
I
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N
F
N
NO
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I
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NNT
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6
O
. I
+
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6
.l
ON
o
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llNl
ll-FFll
IrFNN
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a
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60
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rtttt
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tltll
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ll
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llO
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-
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t€
ar
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r
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l
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lhrä ää äääällgl:l aHäe ägä;lä ä ;H äa
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F
-76Table 52 shows the family composition of the spiders in this meadow.
Spiders of the families Lycosidae and Micryphantidae predominated.
Moreover, spiders of the family Tetragnathidae (genus Pachygnatha)
repeatedly fell into the pitfall traps.
Table 53 shows the composition of the spider species frequently found
of the cultivated meadow C3. The wolf spider species
palustris (1.) and P. agrestis as well as the Micryphantidae
Erjgone atra (Blackw.), Erigone dentipalpis (l,lider) and Oedothorax fuscus
(81ackw.) were the ones most frequently found in pitfall traps. Sjmilar
on the ground
Pardosa
observations were made
Most spiders
living
in other cultivated meadows.
soil surface of cultivated
on the
neadows
are
of
small
size (Micryphantidae, see Table 13). The wolf spidens' and among
these the genus Trochosa, are the largest spiders found on the ground
body
surface of cult'ivated
3.2.3.
meadows.
Seasonal change
of
abundance
following seasonal trends for the predominant species can be derived
fron Tables 54-55: Adult stages of T. pinicola, I',l. acalypha, X. cristatus
The
and X. kochi were ror the most part found in June and innature stages
mostTy-EEffien July and August. Adult stages of N. bimaculata and
T. impressum could be collÄcted in July mäinly. fi-n ova6, immature
itagälGFd-captured jn June, adult stiges in July/IlgusTllo trends
could be established for the rest of the predominant spiders, as the
number of captured spiders was too low.
In Table 56, the spiders' relative densities (= number of spiders/100
sweeps) is recorded for different dates fr"om May to August. It shov,,s
therefore the spider density as a function of the season.
total density (immature + adult stages) in the vegetation zone of
cultivated meadows is far lower than in abandoned grasslands; it
'increases from June to July/August. This can probably be explained by
the fact that the number of irfinature spiders greatly increased during
that period of time (see 3.1.3.1.). tlith a few exceptions, however, by
June most samples already contained more imrnature than adult spiders'
Ground-dwe'lling spiders were found in cultivated meadows from spring to
The
autumn (about 6-7 months/year).
3.2.4. Spatial distribution of
spidens
3.2.4.1. Vertical distribut'ion of spjders
As can be derived from section 3.2.1,2., most spiders in cultivated
Iive near the ground (>90%). A predatory pressure on insect
populations exists therefore primarily near the ground of such meadows.
meadows
3.2.4.2. Horizontal distribution of spiders
For
all the spiders present in the unmown vegetation
zone
of the culti-
vated meadow C4, the index of Morisita was calculated (Table 57). A
distnibution, which did not significantiy differ from a random distribu-
tion (F-test, p >0,05), was found'in this meadow in mid-May.
In two cultivated meadows (C1 and C5), the index of Morisita
ated
for all the spiders of the ground surface (Table 57).
was calculThe values
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lslRl- odo o
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'-l
d6l!l
6l
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_rEl#tFl
Plolxlxl
6ltldldl
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sFJfl
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-79Table 54. Relatjve density
ders/.l00 sweeps)
dows
of the immature and adult spiders (no. of spiin the vegetation zone of the cultivated mea-
Cl (spring 1979) and
C4 (summer 'l979).
i = inrnature stages, a = adult stages
Spider fami
Meadow Cl
1y
Agel eni dae
Aranei dae
Tetragnathi dae
23.5.
t
Mi
cryphant i dae
i
2.6
t.t
t
0.2
2.8
0.9
?.0
i
3.0
a
0
0.8
0.2
3.0
1.0
i
n
0
a
t
0
0
0.1
0.1
j
0
0.2
a
0.2
0.2
0.4
'i
0.8
a
0
0.9
0.2
t
Theridi idae
Di
ctyni dae
Salticidae
Thomi
s
i dae
Pi
sauri dae
Lycos i dae
0.6
t
0.8
l.t
a
U.L
0
i
a
t
0
0
0
0
0
0
i
1.2
0
a
0.9
2.1
0.9
0.9
i
0.4
0
a
t
0
U
0.4
0
i
0
0
0
0
0
0
0
0
t
Philodromidae
0
a
t
Linyphiidae
0
5.6.
'i
a
Cl ubi oni dae
t
t
0
0
Unident. spiders
i
0.2
0
1
8.2
J.U
9.7
2.7
5.7
Total
a
t
I.5
29.6.
Meadow C4
12.7. 6./7.8.
000
0.2
0
0.2
0
0.4
0
1.2
4.5
0.6
0.s
I .8
5.0
1.2
0.5
0
0
1.2
0.5
0.6
0
0.?
0
0.800
].8
0
1.0
0
2.8
0
0.2
0
0
4.0
0
0.5
0
4.5
I 4.0
125.5
1.2
0
1s.2 25.5
0
0
0.4
0
0.4
0
00
0.4
0
00
0.4
0
00
0
0.5
I 35.0
19. 4
J.ö
I .0
23.2
136.0
1
0.2
0
0.2
6.2
6.4
12.6
0
0.4
0.4
0
0
0
1.4
1.4
0.2
9.4
0
9.4
56.4
0
56.4
0.?
0
0.2
0.2
i.6
0.2
1.8
0
0.4
74.6
8.6
83.2
-80of the inmature and adult spiders (no. spiders/100
sweeps) in the vegetation zone of the cultivated meadows C5, C6 and
C7 in surmer 1979. = inmature stages, a = adult stages
Table 55. Relative density
i
Meadow C5
Spider fami ly
II
.6.
23.7
Meadow C6
.
26.6.
l3:1:
t
Meadow
13.8.
12.6.
t
r 'b
,l.6
0.3
0.3
0.6
0
0.6
0.6
0.]
0.3
0.4
0.1
00
0.1
00
00
00
0
00
0
0.1
00
0
00
0
Clubionidae
i
0.,l
0.2
0
0
0
Unid. spiders
i
0
0.2
0
0.8
0.8
00
0.6
0.2
0.8
2.0
I .4
3.4
00
0
0
00
0.4
0.4
0.4
0
0.4
00
00
00
0
0.2
0.2
l0
4 .4
5.4
00
00
0
00
0
00
0
I
t.5
2.4
3.9
5.8
0.2
0.9 9.8
0.8
2.8
't
.7 12.6
12.2
1.2
I 3.4
4.0
6.6
10.5
Agel eni dae
Aranei dae
i
a
t
Tetragnathi dae
i
a
t
Li nyphi i dae
i
a
t
Mi
cryphanti dae
i
a
t
Theri di i dae
i
a
t
Di
ctyni dae
i
a
t
Salticidae
i
a
t
Thomi
s
i dae
i
a
t
Phi I odromi dae
i
sauri dae
i
P
i
Lycos i dae
i
a
Total
a
t
0
0.1
0.3
0.4
0.6
0
0.6
1.4
0.2
1.6
0
0
0
0.4
0
0. 4
0
0
0
0
0
2.0
2.0
0
1.0
1.0
6.0
0.1
0.3
0.4
0
0.1
0.1
0.3
0.1
0.4
0.1
0.1
0.2
00
0.]
0.t
00
0.1
0..l
0..|
0
0.1
0.3
00
0.3
0
0
0
0
0
0.4
0.2
0.6
0.6
1.6
3.8
0
0
I .6
3.8
n
0.6
1.4
0.4
0.4
1 .8
1.2
0.2
0.2
t.6
0
0
0.2
0.2
I .8
1.8
U
0
0
0
0
0
0
0
0
0.2
0.2
0
0
0
3.0
0.6
0
3.0
0.6
0.2
0
1.2
0.4
].0
5.4
0.2
0
1.2
5.4
C7
19.7.
1.5
0
1.6
7.6
0.4
8.0
0.6
0.6
0
0
0.4
0.6
1.0
1.8
0.2
2.0
38.8
0.8
39.6
0.2
0.2
0.2
s0.6
2.6
53.2
of the spiders (no. of spidens/100 sweeps)
in the vegetation zone of five cultivated meadows near Zurich (spring/sunmer 1979). N = number of sweeps
Table 56. Relatjve density
Locati
Meadow
No. spiders/100
on
Seas on
inmature
cl
23.5 .1979
I 250
8.2
c'l
5.6. I 979
800
3.0
c4
29
.6.1979
500
19.4
c4
12.7.1979
200
135 .0
c4
6-7.8.1979
500
7
4.6
c5
il
.6. 1 979
I 000
1.5
c5
23.7 .1979
500
5.8
c6
26.6.1979
800
0.9
c6
16-18.7.1979
500
9.8
c6
I
3.8.1 979
500
12.2
c7
12.6.1979
500
4.0
c7
19.7 .1979
500
50. 6
sweeps
+ adult =
total
r .5
2.7
3.6
1.0
8.6
2.4
0.2
0.8
2.8
1.2
6.6
2.6
9.7
5.7
23.0
136.0
83.?
3.9
6.0
1.7
12.6
13.4
10.6
53.2
-82
Table 57. Horizontal distribution of the spiders in the vegetation zone
(A) and on the ground surface (B) of cultjvated neadows near
Zurich. The data were investigated with the square method. Values with * deviate significantly from 16 = I (F-test, P <0.05).
Stratum
Locat i on
A)
c4
B)
cl
+
c1
+
Date
Mown
15.5.'l979
,l3.6.1979
Squares
i
ta
index
16
Mori
s
964
0 .70
80b
I .03
26.7 .1979
40b
.l.76*
c5
27
.6.1979
loa
'I
c5
26.7 .1979
40b
I.l8
a Square of 0.4 m x 0.4
b Sqru". of 0.2 m x 0.2
m
m
.05
-83show
that the horizontal distribution of the spiders of the
represented a random distribution as
two
meadows
well (F-test, p >0.05) or, at
the
most, a slightly aggregated distribution (C1, July: F-test, p <0.05).
From these spider distributions, a corresponding distribution can be
derived for the predatory pressure which the spiders exert on insect
popul ati ons
.
3.2.5. Prey capture of spiders
3.2.5.'l. Hunting strategies
The
quantitative composition of the spiders, grouped according to their
hunting strategies, is conpiled in Table 58. It shows that the spectrum
of hunting strategies used by the foliage-dwelling spiders differs from
meadow to neadow. In certain cultivated meadows the web-building spiders
predominated, in others the hunting spiders were more prevalent, even though
no qualitative differences could be detected between the types of meadows.
Fron the fact that far more web-building spiders (mainly I'licryphantidae)
were caught in pitfall traps than cursorial spiders (Lycosidae) - Micryphantidae having a lower "activity density" than the Lycosidae (HEYDEMANN,
1962) - one can gather that the former hunting strategy is the most
frequently adopted on the ground surface.
3.2.5.2. Prey
composition
Vegetation zone
- The prey compositions of the
consisted for the most part of
shown in Table 59 for N. cornuta.
Orb-weaving spiders and space web spiders
orb-weaving spiders
in cultivated
meadows
small flying insects (Diptera). This is
of the Dictynidae, Linyphiidae and Theridiidae, too, was mainly
composed of small flying insects (Diptera, aphids).
The prey
- The prey composition of foliage-dwel'ling crab spiders
'in cultivated meadows is represnted in Table 50. The table indicates
that they prey mostly on Diptera (about 60% of their food). The prey
Hunting spiders
in importance are the Hymenoptera (about 16%). Anong these,
large and well-anned prey insects as bees and bumble-bees are found.
group second
even
Ground surface
-
The prey composition of the I'licryphantidae living in
represented in Table 61. The table shows that the
food of the Micryphantidae consisted exclusively of small, soft-bodied prey
organisms. Aphids, Diptera, and Colle,rnbola (predoninantly Sminthuridae) were
the most important prey components. Table 62 shows which Collembola and
aphid species were captured by the Micryphantidae. The cereal aphids
Rhopalosiphum padi L. and Sitöbion avenae F. were also found among the
captured aphids.
lleb-building spiders
cultitäted
meador{s
is
- The prey composition of the Lycosidae living in cultiTs represented in Table 63. The table indicates that the
prey of the Lycosidae in meadows consists for the most part of small,
Hunting spiders
nfiAl
m-eadows
-84-
in percent of the hunting strategies used by the spiin the vegetation zone of five cultivated meadows near Zurich
at different seasons in 1979. The frequencies were calculated from
the data of the Tables 44-48.
Table 58. Frequencies
ders
Location
Season
Hunting strategy
May
Meadow
J
July August
une
b
cl
0rb-weaving spiders
Space web spidersa
Hunting spiders
Unident. spiders
c4
Orb-weaving spiders
22.62
3. 57
0
8. 70
Hunting spiders
0rb-weaving spiders
Unident. spiders
Orb-weaving spiders
Space web spiders
Hunti ng spiders
Unident. spiders
LI
16.67
15.22
69.57
Hunting spiders
Lb
32.61
21 .74
Space web spiders
Orb-weaving spiders
Space web spiders
Hunting spiders
Unident. spiders
57.15
52.17
Space web spiders
Unident. spiders
c5
59.02
10.66
21.57
4.92
Total
bhb
0
51 .29
43.58
5.12
0
28.57
50.00
21.43
0
39.63
7 .54
52.83
0
a The expression "space web spiders" refers to
constructing an orb-web
4.05 8. 17
0.37 2.16
95.59 89.I8
0.37 0.48
6.47
4.36
88.66
0.37
36.66
44.92
6.67
27.54
53.33
26.09
3.33
I .45
17.46
30.17
46.03
6.35
I
8.05
32.84
1,l.94
47.77
7.46
25.69
23.60
44.45
6.25
21.63
3.0.l
3.76
78.58
74.29
0.38
0.31
all web-building spiders
not
-85
Table 59. Prey composition
the cultivated
of
Nuctenea cornuta in
meadow C9
(spring 1979).
Prey type
May
June
ptera
95.95
83. 48
Di
l
0
0.87
t,linged aphids
2.39
0.87
Lepi doptera
0
0.87
Tri choptera
U
2.61
Ephemeroptera
0.18
0
Smal
Hymenoptera
0
2.61
Unidentified prey
1.47
8. 70
No. prey items
543
115
EE
27
2
2
Col
eoptera
No. webs
No, observation days
86-
of foliage-dwe1ling
Table 60. Prey composition
dwell ing crab spiders
in cultjvated
Zurich (data from several
and
of
ground-
meadows near
meadows combined, study
years 1976-1978).
Foliage-dwe11ing
Spider
spiders
(Xysti cus spp. )
N = '134
crab
group
'ition in
Ground-dwelling
crab spiders
(Xysti cus spp. )
N=
37
%:
Col I embol a
0
0rthoptera
0
5.7
)q
Thysanoptera
4.0
U
Heteroptera
0.8
?.9
Ci cadas
0.8
Aphi dae
0
il.4
Carabi dae
0
5.7
0ther Coleoptera
4.8
D i ptera
64.
Lepi doptera
Ap
0ther
B
1.6
0
4.8
Ants
Hymenoptera
Spiders
Lumbricide
worms
2.9
0
4.0
i dae
2.9
0
34. 3
8.0
2.9
6.4
25.7
0
2.9
-87
6'l.
Table
of small ground-dwelling web-building spiders
(nrainly Micryphantidae) in cultivated meadows near Zurich (stu-
Prey composition
dy year 'l977).
C2+C4
Prey
N
c8
N
ClO
NN
Total
Col I embol a
53
12
10
75
45.45
Apterous aphids
l5
24
0
39
23.64
2.42
nged aphi ds
2
2
0
4
Small Diptera
7
4
I
t2
Small Hymenoptera
J
l
2
6
3.64
Thysanoptera
3
I
I
q
3. 03
2
J
n
5
3. 03
4
0
0
4
2.42
0
0
I
0.6i
I
n
0
I
0.61
insects
0
2
0
?
I .21
Unidentified prey
a
I
?
ll
6.67
99
50
l6
165
l,li
Mi
tes
Smal
I
Smal
1 Heteroptera
cicadas
Snall orthoptera
Larvae
Total
of
,l
7
.?7
100. 0
-88-
of Collembola and aphids in the food of small ground-dwe11ing
web-building spiders. Observations in cultivated meadows near Zurich
Table 62. Species
(year 1977).
Group
Meadow Meadow
Speci es
CZ +
Fami 1y
C4
C8
Meadow
Clo
ColIembola
Sminthuridae
Sminthurus
viridis
bilineatus
Deuterosminthurus flavus
Dicyrtonina minuta
Entomobryidae 0r"chesella villosa
Heterosminthurus
Lepidocyrtu: Ianuginosus-group
gen. spec. inmature
Isotomidae
Isotomurus
palustris
Aphi ds
pad'i ar
Rhopalosiphum padi? i
Sitobion avenae I
Anoecia corni
o
Pemphigidae
u)
Rhopalosiphun
I I = larva, a = apterous, r,l = winged
+++
+
+
+
+
+
+
+
+
-89-
lable 63. Prey composition of wolf spiders (Pardosa spp.) in cultivated
meadows
near Zurich (study years 1977 and 1978).
-4.6
O
-o
4
E
o
o
6O
op
o6
JO
o
O
c?
6.9.
c4
8.
8.
c4
c4
9.
q
F O
-c
EO
I
o
!
.r
o
@
q
c
'|
9.
10.9.
l
I5.
9.
17.
9.
c4
21
c4
22.
c4
-t
c4
24.9.
26.9.
-l
-2
I-
.9.
9.
c4
4.10.
c4
5.10.
c4
7
E
!
@
.-o
9!
.-O
PÄ
Eö
o!
!S
<!
I
c4
I
-l
;
5
3
2
.10.
I
i-
cb
6.
I-
6.
c4
1?.6.
12.6.
c4
30. 6.
c2
o
!
o
P
oo
!d
-F>
q!
a €
Fr
21
c4
c4
O
q
E
d
E
€
O
'I
F
r
E
I
'I
I
I
c2
3.
7.
I
c2
15.
7.
'|
(3)
a Possibly a small hymenopteran
b Meadow near Zurich-Weiningen
17
-90soft-bodied prey organisms. Aphids, Collembola (e. g. 0rchesella vi I losa
(Geoffroy)), and Diptera seem to form the most importäiT-f-ifüornponents
of the Lycosidae.
Occasionally, crab spiders (X. cristatus) were also seen on the ground
surface of cultivated meadows. Especially after mowing, ground-dwe1ling
X. cnistatus were rather frequent. Table 60 (right column) gives informaTTon-on-lirE-tood composition of such crab spiders. They fed mainly on ants
and spiders (e.9. wolf spiders). In addition, they captured aphids, Carabidae,
and Collembola (e.9.Orchesella villosa (Geoffroy)). Even small lumbrici de worms were preseiT--ä-Thd-fö6d--ö-f giound-dwei i i ng crab s pi ders .
As the prey compositions (Tables 59-63) indicate, the spiders living in
cultivated meadows catch neutral insects (e.9. Diptera), pest insects
(e.9. cereal aphids),
and
beneficial insects (e,9.
bees).
3.2.5.3. Prey size
living in cultivated meadows captured mainly smal1,
soft-bodied prey of merely l-3 mn body-length. Such prey organisms
have a fresh weight of only 1-2 mg.
Most spiders
3,2.5.4. Prey capture rates
l0 insects/web/day on the average were counted in webs of
N. cornuta in the cultivated meadow C9 in May 1979.
0f the hunting spiders, less than l0% of a population were found feeding
at any given time (Tables 64-66). Adult wolf spiders (P. agrestis) spend
about 45-60 min for the consumption of a small pney (Table 67). These
data being known, the prey capture rate was calculated by neans of the
About
method of EDGAR (1969,1970) (see
i tem/spi der/day.
3.2.6.
of
Niche
iders concerni
amounts
to
about
I
prey
food
Araneidae and Thomisidae show a large overlap
Both spider families feed on small Diptera for the most
The prey compositions
at order level.
2.3.8.2.). It
of
part (see 3.2.5.2.).
of Micryphantidae and Lycosidae had relatively
'large ovenlaps at order level, too. Both spiden families lived mostly
on small, soft-bodied prey organisms (aphids, Collembola, Diptera).
The prey compositions
3.2.7. Predator-prey relations between crab spiders and wolf spiders
In cultivated meadows, crab spiders come occasionally into collision
with wolf spiders, especially after mowing. If one looks at the
chelicerae of the two spider families, it should seem that the highly
active Pardosa species, which have significantly larger fangs than the
clumsier Xysticus species equipped with only moderately developed
mouthparts, would dominate over the Xystjcus species (Fig. 4).
If one compares the four pajrs of legs of the two spider families however,
it is evident that the two pairs of forelegs of the crab spiders are much
stronger than those of the wolf spiders (Fig. 5). By taking advantage
of the element of surprjse, the crab spiders can defeat well-armed
activity of crab spiders (Xys_ticus spp.). Numbers of
crab spiders captured in the cultivated meadow C4 and percentage of spiders feeding (years 1977 and 1978).
Table 64. Feeding
Hours
Date
of
observati
on
Number of
spi ders
Number of
spi ders
captured
feedi
6.5.1977
l0-'l2
l0
2
14.5 .1977
I4-16
18
0
12.7.1977
I
8-20
t4
5
16.7 .1977
l0-12
90
5
22.7.1977
t6-18
194
14
TotaI
326 (= 100
(1977)
%)
26 (= 7,9s
24.4.1978
l2-16
7
0
26.4.1978
t2-16
I9
4
3.5.1978
12-16
il
2
10.5.1978
l4-,l6
4
0
17.5.1978
l4-16
17
0
30.5. I 978
,l.6.1978
t6-18
I
0
l0-,l2
J
0
6.6.1978
10-12
2
0
12.6.1978
l0-12
E
0
Total
(.l978)
Total
(1977
69 (= r00
+
'l978)
39s (= 100
%)
%)
ng
X',)
6 (= 8.70 %)
32 (= 6.1s *,
-92-
Table 65. Feeding
activity of wolf spiders
wolf spiders captured
centage
(Pardosa
in the cultivated
of spiders feeding (study year
Numbers
on
1977).
of Number of Percentage
spiders spiders of sPiders
captured feeding feeding
6.
9.1977
l4- t6
9
0
0
7.
9.1977
'14-
I
I
22
0
0
8.
9.1977
I0-l
10.
9.1977
2
l4
3
l6-18
26
I
t0-l
2
20
0
l4-1
6
17
I
'14-18
27
1
10.0
5.1
14.9.1977
l4-16
21
0
U
15.9.1977
l6-18
23
I
4.3
.
9.1977
l4-.l6
24
I
4.2
21.
9.1977
l4-l
6
20
t
5.0
22. 9.1977
t2-16
53
2
3.8
?3.
't4-16
22
0
0
24. 9.1977
1?-16
36
2
5.6
26.9.1977
t0-14
23
I
t4-18
28
4
4.10.1977
l4-r
6
43
4
5.10.1977
t0-12
l0
0
l4-16
40
4
l0-t
2
20
I
5.0
16-'l8
ö
0
0
t7
7
9.1977
.10.1977
18.r0.1977
TOTAL
of
per-
Number
Hours of
observati
spp.).
meadow C4 and
27
9.8
o1
8.0
5.3
-93-
activity of wolf spiders (Pardosa spp.). Numbers of
wolf spiders captured in two cultivated meadows and percentage of spiders feeding (study year'1978).
Table 66. Feeding
Locati on
and date
Hours of
observati
on
Number of
spi ders
Number of
spi ders
Percentage
captured
feedi
feedi
ng
of
spiders
ng
Itleadow C2:
12.6.1978
12-14
(r0.0)
t0
I
5.0
3.7 .1978
t4-r8
zoa
'I
15.7. t978
l4-,l6
t5
I
(6.7
?
l0
0
(0)
3.8.'l978
Total
)
5.5
Meadow C2
Meadow C4:
.4.1978
t4-t6
21
0
24.4.1978
l2-16
25
I
4.0
.4.1978
12-16
40
0
0
20
26
0
3. 5. 1 978
12-16
24
I
4.2
10.5.,l978
t4-16
20
1
5.0
.5.1978
r4-16
20
1
r .6. I 978
t0-12
't0
.6. r 978
t0-12
t4
I
(7.1)
12.6.1978
'10-'l2
12
?
(r6.7)
30.6. I 978
l0-'l4
l8
I
17
6
Total
Meadow C4
Total
Meadows CZ
0
5.0
(0)
5.6
3.9
+
C4
a Incl. Pirata spec.
259
4.3
-94-
dl
ol
ol
LI
6l
o
o
c
o
d
o
NN
o
o
E
o
o
0
6
E
E
d
+l
o
o
I
c
!
o@o+6
ONNO
ltttl
rx
6
oNo6
FO@ON
6++@$
<r;-;c;.;
o$No
+r +r +.
oooN
ONtsO
+.
+l
@
1
N
N6N@@
+b6@
J
d
z
A
o
o
L
o
o
o
o
o
d
e
OL
o
EP
o6
po L
qo
E6
co
o<
AP
oq
!l
o5
pt
co
oo
aE
60
o
o
6
+l
o
rx
d
=
6E
oo
po
=!
c
E6
q ol
oNoo@
ONNON
tttrl
o6
@@@N
N
N@OO@
@NNO
6N6N
o+ob
+r +r
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@6000
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+r
+r
FOI
.:
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o
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d
+r
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€N60
6^
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PEE
O6.F
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o€o
PO60
A.-!€
-@o! d6
-Pl
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ot
F
LI
.=
ut
o
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6
F
***
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6SOOO
EOE<
o
o
=
EO
c
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=
95-
9-1.9
Fig.4.
Fiq.
-' 5.
-
of the mouthparts ot crab spiders
) and wolf spiders (Pardosai;ü".t.-rne dirierent formation of the chelrcäraä or the two spider fanrilies is an expression of different feeding behaviours'
Comoarison
lXvsticus
spp.
-
of the habits of a crab spider (iysl!s!: sp')
i"a'of a wolf spider (Pardosa sp' )'
comparison
-96arthropods (e.9. wolf spiders) with the help
of
these legs. In al1
confrontations observed between'individuals of the two spider
the wolf spiders were always killed by the crab sp'iders. Crab
are potential predators of woif spiders. It has been observed
Great Britain and Japan that crab spiders killed wolf spiders
'1974i 0'NEILL, pers.
comm. ).
3.2.8.
families,
spiders
also in
(ORI,
flow through the ground-dwelling sp'ider communjties
was not investigated.
But the energy flow (= food consumed) through the ground-dwe11ing
Energy
The prey
killing rate of ground-dwelling spiders
web-building spider guild could be estimated by means of the method
.l55-419
described in section ?.3.10.2. It was calculated to be about
kJ/
halday. Supposing 100 activity days per" year, this would anount to
'15-40 MJ/ha/year.
3.3.
The
3.3..l.
role of spiders as insect predators in cereal fields
Inrni
tion into cereai fields
of immigration, the time of harvest and the spiders'
of stay in the fields are cornpiled in Table 68. The va'lues in
the table indicate that spiders can live in cereal fields only for a
limited length of time, from the time of imnigration to the tjme when
the fields are harvested. The harvest is a severe stress for the spiders
of the vegetation zone (destruction of the living space and the spiders'
egg sacs). For this reason, a recolonization of the fields from the
surrounding land is necessary every year. As a consequence of the
periodic disturbance of the spider population through mowing, the
spider densities in the vegetation zone of cereal fields are very low
Data on the time
duration
(Tab1e 68).
To what
extent the soil cultivation'influences the
ground-dwe11ing
spider populatiohs, was not examined within the framework of this thesis.
Compared to the vegetation zone, the spider densities on the ground
surface of ceneal fields are relatively high (Table 69).
3.3.2. Spider comnunities of cereal fields
3.3.2,1. Vegetation
zone
family and species composition of the foliage-dwelling spiders in
cereal fields was investigated by direct observations. The data of
jn Table 70. Further observations in the years
1976-1977
,l978-198] are compiled
were not made quantitatively.
Web-building spiders of the families Araneidae (Araniella
cucurbi ti na/opi sthographa*, A. ceropegi a, N. cori'ffil-Tl-acalypha ),
Tetragnathidae (T. extensa, T. pinicola), Theridiidae (T. impressum a.o.)
and Linyphiidae (1. triangularis a.o. ) prevailed in the vegetation zone
of cereai fields.
Hunting spiders of the family Thomisidae (Xysticus spp.) were only rarely
The
observed.
Araniella cqqqlqj!i!q (C1. ) and Araniella opisthoglapha (Ku1cz. ) are
iwolpecTe; wtricl couta not oe vlsuä]lv?'lstinguETre,a'-Tn the f ield.
-97!
po
o
o
@
gONN
O O Ets
o
dt!N
F'F
OO
S 6la <.F
ooec
dE
a'-
o
o
F
o
E
o
!
6
o
c
90
o'r
E @!
O NP C.F
!
O
ä
o
o9 od>
lF
o= os!
a ov
ooo
€ro
:
o=
o
=
6
c
o
!
6
o o$
.FL
poo
N
g
o.
9<
o!
CN =
o
.-!
PO
do
!c
=
90
!
PO
os
L60
EO
!
$o
oa
o9
EO
PO
.o c
gN
o
I6Eg
O !'FP
oo
O.- o O
o.-
F.F
ogo
o!
C.F O^
6
oP
PpEd
€oP!
!o
> @9
ö>ö
4)@
c<
f5
DD
OP o
o
6d:
=
oo
a@
ror o
OO
!
Ao
Oo
o
o>
EI
FS
rfa
D-O
PO
6'r
!p
o6
Eöo
soo
g
!!
oo
qP
ts.-
oo!
!!
ooo
c;
@
o
o
F
o
O
!!
ooo
E!N
f.FO
a==
98-
Table 69. Density of the ground-dwelling web-building spjders in three
maize fields and in two winter wheat fieids near Zurich (study
years 1978 and 1979).
Locati
on
Date
Crop
654
13. 38
2.6. 1 978
zoa
19.00
14.7.1978
zoa
35.00
.6.1978
40b
16.5.1979
50c
53.I3
1I.88
mar ze
chbuck
maize
1
Reckenhol z
maize
Reckenho l z
winter
winter
Mi I
n
Reckenhol z
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In contrast to abandoned grasslands, jumping spiders and large funnel web
spiders v.,ere only seldom encountered jn cereal fields. The same js true
for A. bruennichi and A. quadratus, which predominate jn abandoned grass-
ands]--It is conspicuous that the spider fauna in the vegetation zone of cereal
fields consists to a large extent of orb-weaving spiders (Araneidae,
Tetragnathidae). The Araneidae found in maize fields show a significantly
higher percentage of immature stages than in the rest of the cereal crops
(x' 2 * 2 contingency table, p <0.01). The almost comp'lete absence of
adult orb-weaving spiders in maize fields might be explained by the fact
that maize develops a dense plant stand much later than the other cereals.
The composition of the spider fauna differs from field to field. In each
case, however, it depends on the surroundings of the field.
Predominantly medjum-sized species (see Table l3) are found among the
adult foliage-dwel ling spiders, A. ceropegia being the largest species
in cereal fields,
I
3.3.2.2.
Ground surface
family and species compositions of spiders established by means of
on the ground of winter wheat f.ields are compiled in
Tables 7l-73. Spiders belonging to the famjlies Micryphantidae and
The
pjtfall traps
Lycosidae predomi nated.
In Tables 72-73, the composition of spider spec'ies captured frequently
on the ground surface of winter wheat fields is l.isted for the years
1977-78. P. agrestis, P. palustris, E. atra, E. dentipalpis, and
Oedothorai apr-catus (Blackw.) were the most frequent species found in
p;tfal-fraps. Sitmflar results have been obtained in 'l979. Comparable
data were also collected in other cereal fields.
Most spiders living on the ground surface of cereal fields are of small
body size (Micryphantidae, see Table 13). l,lolf spiders of the genus
Trochosa are the largest spiders on the ground of cereal fields.
3.3.3.
Seasonal change
3.3.3.1.
of
Seasonal change
abundance and
of
dajly activitll
abundance
occurrence of the predominant spiders in the
seasonai development of the cereal vegetatjon.
As the table indjcates, most spiders migrate into the vegetatjon zone
of the fields in spring only after the stem elongation has occurred.
The coloniz'ing spiders come from small, jntact marginal biotopes' such
in Table 74, the seasonal
fields is compared to the
as stripes of meadows, and forest fringes. From the time of imm'ignatjon
up to the harvest, the spiders spend only 60-70 days in cereal fields
and about i30 days in maize fields (Table 68).
The ground-Cwe1 1 ing spiders show statistical ly si gnif icant differences
of abundance in different seasons (analysis of variance, p <0.01).
3. 3. 3. 2. _D3-t-li_9!t,'L1!y
The orb-weaving spider !.--Sg11-qE
is p!evalently nocturnal. Fig.
6
Table 7.l. Family composition'in I of the ground-dwelling spiders in a
winter wheat field near Zurich-Reckenholz (year 1978; traps
dug into the ground on May 21).
Spider fanily
I'li
cryphanti dae
Lycos i dae
Traps emptied on:
4.7 .
3l .7.
Total
l8
N=874
.6.
19.6.
N= 89
N=432
1
N=l
87 .6
52.6
88. I
il.2
44.0
8.4
Tetragnathi dae
0
0.9
0.8
Li nyphi i dae
0
1.2
0
Thomi si dae
0
'l .l
0.?
0
1.2
2.5
Unidentified spiders
Total
100
.0
100
.0
N=235
94.5
0. 4
0
0
0
72.4
24.1
0.6
0.6
0.]
4.3
100.0
100.0
-102-
Table 72. The dominant ground-dwe11ing spider species jn a winter wheat fjeld
near Zurich-Reckenholz (year 1977' traps dug into the ground on May
t7).
Traps
Spider species
26.5.
502
N=
Erigone atra
o
Erigone dent'ipalpis
ö
Erigone atra
Erigone dentipalpis
I
I
0edothorax spi catus
d
!g4g!!9rgr
fusc_u_s
d
0edothl'rax
ap'i
catus
?
oedothorax fuscus
I
gSI$!_:.
Pardosa palustris
d
Pardosa
Itfqgj-q
agrestis_
Pardosa pal ustri
s
6
I
I
3.6.
373
N=
emptied
18.6.
5.7. 20.7.
3.8.
N=1490
N=1647 N=4289
N=4572
33
20
0
n
0.3
0.5
0
0
0.3
0.9
93
0
29
l6
3
74
< 0.5
on:
44
6
50
1a
36
0.8
0. 4
ZJ
l9
0.7
0.7
20
0.3
o.u
16
9
6
35
13
4
0.2
4
13
2
0.2
0
0.'l
2
I
U.J
2
0
0-l
0
0
0.3
< 0.5
I
29
36
.04
-103-
Iable 73. The dominant ground-dwe11ing spider species in a winter wheat
field near Zurich-Reckenholz (year 1978' traps dug into the
ground on May 2l ).
on:
Tr"aps enptied
1.6. 19.6. 4.7. 31.7. Total
N= 89 N=432 N=ll8 N=235 N=874
Spider species
3l
atra
o
!1
Erigone atra
I
0
Erigone dentjpalpis
d
24
Erigone dentipalpis
o
0
0.7
2
oedothorax apicatus
0edothorg apicatus
d
6
3
9
Pardosa agresti
s
o
Pardosa agresti
s
I
Eni gone
Pardosa pal ustri
9
s
ö
Pardosa palustris
o
829
t3
211
00
0.7
18
8
2.5
30
26
0
t8
0.9
?5
0.7
20
0.8
t9
28
14
2.2
0
16
4
0
2
0
0
6
0
0
J
6/e
ri'
them 7,6% males of Erigone spp.
with destroied pedipalps
other spiders
a Among
24
21
8
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_106_
represents the feeding
activity
and number
of
prey/web
of N. cornuta at
different daytimes. This spider species captures its prey äI-iiglTln
the following manner: The web-building actjvity is induced in the
twilight, when the intensity of the light drops below a critical
intensity. The building of an orb-web requires 30-60 minutes. At about
the same time, the flying activity of many cereal insects active at
night or in the twilight begins. Tipulidae, Noctuidae, Pyralidae, and
evening
Chrysopidae begin to f1y about, and many small Nematocerae swarm in the
flowering zone of the field, where the orb-webs, about 25 cm in diameter,
have been built, These now continuously filter the swarms of nocturnal
flying insects. Most of the prey gets caught in the webs between 20.30
22.30; during these two hours, the spiders captured 10-20
prey items/web on the average. The hungry spider starts feeding inrnediately after having built the web.-The highest-feeding activity lies
between 22.00 and 24.00. Since only occasionally prey organisms
fly into the webs after 22.00, the webs are gradually emptied through
the spiders' feeding activity. The spiders' feeding activity diminishes
after midnight and ends towards daybreak. The spiders then retire into
their retreats where they hide during the day.
I'lost of the other orb-weaving spiders were observed feeding during the
day and at night (e.9. A. diadematus and A. ceropegia, Table 75). Space
web spiders of the families Theridjidae, Linyphiidae and Micryphantidae
are also diurnal and nocturnal, whereas wolf spiders of the genus
qCl4glq are prevalently diurnal.
and
3.3.4. Spatial distribution of spiders
3.3.4..l. Vertical distribution of spiders
we find spiders from the ground surface up to the
flowering zone (Table 76). As can be derived from section 3.3..l.2.,
spiders ljve near the ground (>90%).
In cereal fields,
most
3.3.4.2. Horizontal distribution
In ]977 and 'l979, the horizontal distribution of the spiders of the
vegetation zone and the ground surface in winter wheat fields was
studied by means of the square method, and the index of Morisita was
caiculated (Table 77). The observed distributions of the foliage-dwelling
spiders did not statistically deviate significantly from a random
distribution (F-test, p >0,05). The sane'is true for the distribution of
the ground-dwel1ing web-building spiders (Micryphantidae) in the winter
wheat fields as well as in other wheat fields and in two maize fields
(F-test, p >0.05). However, a slightly aggregated distribution was noted
in another maize field (F-test, p <0.05).
The horizontal distribution of the ground-dwelling spiders was also
studied by means of pitfall traps in a winter wheat field at different
seasons. Although the Figs. 7-18 give only the activity-densities of the
ground-dwelling spiders, the figures may be regarded as graphical
representations of the horizontal distribution of these spiders. The
Figs. 7-12 show the horizontal distrjbution of the Micryphantidae at
different times of the year. A comparison of the capture rates of the
traps on the border of the fjeld !,ith those in the centre did not
show
-107-
Table 75. Feeding
activity in % of
two orb-weaving spiden
species (% f) at different times of day in an
oat field near Zurich-Höngg in summer 1976 (N =
no. spiders observed). Activity values followed
by the same letter differ significantly (12
test 2 x 2 contjngency table, P < 0.05).
Hours
of
observati
A.
on
00-04
04-08
08-t
2
12-16
16-20
20-24
A.
diadematus
N
%f
33
60
112
25
l1
48
21.2
d
]0.0
ac
25.0
20.0
63.6
27.1
a
ceropegia
N
22
12
II
9
b
abcd
c
%f
18.2
25.0
45.5
22.2
Table 76. Vertical distribution of the orb-weaving spiders and of Achaearazone of a winter wheat field'near
nea ripar"ia in the vegetation
.l979;
the vegetation was l'2 m high.
Zurici-Reilienholz in June
Height of
orb hub
0ther
Al
Achaearanea
1
orb-weavers orb-weavers
above ground
rr parl
a
(crn )
- r25
75 - ]00
50- 75
?5- 50
0- 25
100
Total
?
0
6
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l6
42
12
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0
0
63
36
3 (3%)
25 (25 %)
58 (59 %)
r3 (r3 %)
0 (o%)
38
(r00
%)
ee (ro0
38 (r0o
%)
%)
0
(0%)
(0%)
0
(0
0
(0%)
0
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Fi
gs.
7
109
-
distribution of the ground-dwe11ing sheet-web
spiders (mainly Micryphantidae) captured by pitfall traps
in a winter wheat field near Zurich-Reckenholz in the year
1977. Each square represents a pitfall trap. The number of
points per square represents the number of spiders captured per trap and pen time unit. A horizontal balinstead
of a number means that the pitfall trap vias destroied. The
distribution of the squares corresponds with the distribution of the pitfall traps in the field (comp. Fig. 2).
-12. Horizontal
(Fig. 7), June 3 (Fig. 8), June 18
(Fig. 9), July 5 (Fi9.'10), July 20 (Fig. ll), and Ausust
3 (Fis. l2).
Tnaps emptied on May 26
Figs.13-i8. Horizontal distribution of the wolf spiders (mainly Pardosa
agrestis and P. palustris) captur"ed by pitfall traps-i-äwinter wheat field near Zurich-Reckenholz (otherwise
as
Figs.7-12, see above). Traps ernptied on May 26 (Fig. l3),
June 3 (Fig. l4), June l8 (Fi9. l5), July 5 (Fis. 16), July
20 (Fig. 17), and August 3 (Fi9. l8).
'I
13
o
16
13
14
l8
12
10
3
t3
o
I
11
4
10
10
I
7
5
14
4
6
7
6
I
10
o
t7
12
13
8
16
7
7
7
13
8
o
4
a
6
I
6
12
I
4
6
6
6
4
4
1
6
a
4
4
2
4
4
2
4
o
10
4
1
13
2
2
o
6
2
2
2
5
5
o
o
o
2
1
2
5
2
57
20
24
54
51
52
15
28
24
27
33
27
39
22
16
24
6
26
38
24
29
34
41
32
46
11
30
17
25
38
36
't6
21
9
15
11
7
11
23
16
Fig.
16
9
14
Fis. l0
52
18
23
35
51
44
25
l4
20
66
24
22
35
46
t8
29
54
13
45
27
6
23
69
31
31
33
40
50
43
40
37
75
39
30
45
52
68
63
31
11
20
21
25
o
30
74
50
5A
70
13
73
61
76
108
a9
122
70
129
159
8.1
125
190
96
67
108
57
115
57
76
r36
90
100
129
144
166
t32
143
254
49
86
63
117
68
65
65
76
t25
8A
79
105
94
109
50
163
75
38
75
120
77
118
102
o
83
t03
117
104
t26
140
117
166
90
109
33
70
62
123
68
164
81
a2
43
84
96
r04
73
Fig.
l1
102
Fi
g. l2
112
Fig.
13
1
2
o
1
4
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7
7
2
15
o
o
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1
3
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3
3
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6
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11
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17
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Fi
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16
4
o
2
I
2
o
2
o
o
o
o
o
4
8
12
o
o
4
o
I
3
1
2
5
3
1
2
4
2
o
o
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1
o
2
2
o
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1
t2
1
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o
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18
o
6
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7
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Fig. l7
Fi
2
5
o
1
1
o
2
6
18
4
5
7
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o
2
4
4
7
6
1
1
34
4
I
112
o
I
o
g. l8
3
-il4statistically significant differences (t-test*, p >0.05).
worthy edge effect could be detected.
Thus no note-
The same is true for the hunting spiders living on the ground.
A graphical representation of the horizontal distribution of the
Lycosidae in the winter wheat fjeld at different seasons is given in
the Figs. l3-18.
3.3.5. Prey capture of spiders
3.3.5.1. Hunting strategies
Table 78 gives a view over the hunting strategies
of the spiders living
in cereal fields. In the vegetation zone of cereal fields,95-98% of
all spiders capture their prey by means of webs, and only 2-5% catch
their food as hunting spiders without webs. The proportion of orb-weaving
spiders (families Araneidae and Tetragnathidae) of the total of all
web-building spiders of cereal fields was 75-88%.
In the pitfall traps, 75% were l'reb-building spiders and 25% hunting
spiders. This indicates that most ground-dwelling spiders in cereal
fields capture their prey by means of
3.3.5.2. Prey
webs.
composition
Vegetation zone
0rb-weaving spiders - The prey compositions of orb-weaving spiders of
wheat, barley, rye, oat and maize fields are represented in Table 79.
The
table indicates that Diptera (68.8-92.1%),
(4.0-17.5%) prevail
and winged aphids
in the prey compositions of
orb-weaving spiders in
fields. Detailed information on the prey compositions of
orb-weaving spiders in cereal fields are given by NYFFELER & BENZ
cereal
(1979a).
spiders - Table 80 shows the prey compositions of T, impressum
'in wheat and oat fields. Diptera and aphids are the most important
components of the food of T. impressum. The prey of the foliage-dwelling
Linyphiidae in cereal fields aiso consisted mostly of small Diptera and
Space web
Homoptera.
*The asynnetric distribution
pennit the use
of the data
of the t-test.
was
corrected, in order to
ll5
Table 78. The hunting strategies
Spi
der
and/or
of the spiders living in cereal fields.
speci es ,
Hunt'ing
genus
manner
wjdth
(nln)
Mesh
0
cn
}{eb
t^leb area
qn2
3-4
20-30
Araniel la cucurbitina
2-3
6-8
40
Aculepeira ceropegia
l-3
20-30
500
Araneus diadematus
3
15-25
300
Mangora acalypha
I
Nuctenea cornuta
Araneidae gen. sp. (irm.
orb-web
)
Tetragnatha spp.
Pachygnatha degeeri (imm.)
Theridion impressum
Achaearanea
riparia
Linyphia spp.
irregular
tangled
l4
500
150
1-2
2-8
20
3
B-t5
100
2.5
5
web
web
sheet-web
Erigone spp.
0edothorax spp.
Y\ysticus spp.
ambusher
Pqrclqg4 spp. a
runner
a In the literature the Pardosa spp. are usually described as runners.
However, F0RD (1978) found that Pardosa amentata adopts a "sit-and-wait"
strategy with periodic changes of site.
-il6-
Table 79. Prey composition
of
Prey
Rye
of cereal fields
orb-weaving spiders in the vegetation zone
near Zurich (years 1976-1977).
1976
0ats
1977
Mai ze
Wheat
Barley
,x
Hetenoptera
0.2
0.4
1.7
Thysanoptera
0
0.9
5.8
10. 2
0.8
17.5
5.6
12.7
14.8
4.0
0.8
Aph i dae
0
0
0.3
1.7
1.?
0.2
Hymenoptera
0
1.3
0
1.0
0.4
Chrysopi dae
3.9
1.3
0.6
0
0.8
77 .6
71.5
68. 8
375
231
Col
Di
eoptera
ptera
Number
of prey
items
'144
68.4
92.1
412
529
of Theridjon inpr_essum
in the vegetation zone of wheat and oat
fields near Zurich (years 1976-1977),
Table 80, Prey composition
Wheat
Prey
0ats
Ephemeroptera
7.6
Thysanoptera
9.0
I.6
42.6
33.3
3.1
ll.t
Hymenoptera
0.4
9.5
Tri choptera
0
Aph i dae
Co1
Di
eoptera
ptera
Number
27.8
of prey
items
2?3
7.9
7.9
20.6
76
- lt7 -
other hunting spiders were only rarely
zone of cereal fields. Since foliagedwelling hunting spiders (Thomisidae, Philodromidae' Salticidae'
Clubionidae, Pisauridae) appean to live in low densities in ceneal fields
and since only a small percentage of a hunting spider population is
feeding at a given observation time, the probability of surprising a
hunting spider with a prey is exceedingly low. Thomisidae could be
observed capturing Diptera, spiders, and one aphid in cereal fields'
Hunting spiders
oSservea-freeäIng
Thomisidae and
in the vegetation
Ground surface
Web-building spiders - The prey composition of the Micryphantidae of
wheäfinA rnalze TiEi-Us is nepresented in Table 8l . The table indicates
that the food of the l'licryphantidae exclusively consisted of small
soft-bodied prey, aphids, Collembola, and Diptera being the nost
important components. The Collembola captured by the Micryphantidae'
generally belong to the Sminthuridae,
Hunting spiders - The prey composition of the Lycosidae of wheat fields
ITrepresenTü-in Tables 82-84. It also includes mainly small' softbodied prey organisms, especially aphids, Collembola' and Diptera. The
Collembola for the most part belong to the Arthropleona-group (e.9.
Isotomidae and Orchesella villosa (Geoffroy) of the family Entomo6'Eid-ael.
The captured aphids were exclusively cereal aphids (Metopolophium
ai.noaur
tlalk.,
Rhopalosiphurn
padi
L., Sitobion avenäe El-E=jlsted in
Table 85.
Spiders with special hunting strategies
- Adult Carabidae
and Staphylinidae
e and MicrYPhantidae, as both'
the Lycosidäe and the Micryphantidae' are not capable of killing hardbodied beetles. There is, however' a spider species belonging to the
family Theridiidae, Achaearanea riparia (Blackw.)' which often captures
adulfCarabidae and STäptyTlfrl?aä-5y nreans of tangled webs (Tab1e 86)'
As Table 87 sho,rs, several Carabidae-species (mainly of the genus Amara)
were captured by A. riparia. It captured a rather typical selection of
medium-iized CaraEJEää'iITng in cereal fields of Western Europe (comp.
THIELE, 1977, p.27). (A. riparia has been observed killing Carabidae
alsojn
meadows,
witn si6les,-wneie this spider lives, too).
3.3.5.3. Prey size
of the food of spiders in cereal fields consisted of small,
soft-bodied prey organisns of only i-3 nrn body length. Such prey organisms
have a fresh weight of merely l-2 mg.
More than 90%
3.3.5.4. Prey capture rates
Vegetation zone
In order to determine how many insects per day are killed by one web'
continuous observations of orb-webs were conducted on a total of 7 days'
The results of these observations are compiled in Table 88. The table
- lr8 -
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Table 82. Prey composition of wolf spiders (P. agrestis and P' palustris) in a winter wheat field near Zurich (year 1978)'
Index: + = -< 101; ++ = 10-20%; +++ = 20-35fl; ++++ = > 35%'
No. observation days
No. spiders captured
Spiders with prey
Prey
cjrmpos_i
ti
June
6
7
21
?63
242
l0l3
9
10
40
Aphi dae
ptera
518
59
+++
++
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++
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tes
Spi ders
34
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I'li
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July/August
May
++
+
4%
+++
16%
-
120 -
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-122-
Table 85. Aphid species in the food of wolf spiders. 0bservations in a
winter wheat field near Zunich-Reckenholz (June/Ju1y 1979).
a = apterous, w = winged, + = prey of wolf spiders.
tlolf
Aphid species
Metopolophium dirhodum
a
dirhodun
w
l'letopolophium
padi
Sitobion avenae
Rhopalosiphum
of
Achaearanea
Carabidae (see Table 87)
ptera
Apterous ants
t.linged Hymenoptera
Spi ders
Mi
tes
Unidentified prey
No, prey items
I
wheat fields
1979
I 978
other Coleoptera
Aph i dae
riparia in winter
t977
10.6
Ci cadas
+ (June)
+ (June)
a
Staphyl i ni dae
Heteroptera
(June)
+ (June)
0
1.3
00
0
0
26.7 \
* I
Dermaptera
0rthoptera
amentata
+ (July)
near Zurich (years 1977-1979).
Prey
+
+ (June)
a
Table 86. Prey conposition
Di
spiders
P. agrestis P. palustris P.
2.1
0
0
0
l.'l
0.7
3.2
27.0
2.1
5.7
2.1
ro.,
2.6
22.7 | 24.0
I .3 I
0
o
22.7
3.2
6.4
r.r
5.0
8.4
7.1
23,2
l7'0
59.0
35.8
9.2
5.4
0.7
7.4
7.4
14.2
J.5
4.3
17
't4t
.7
26.2
-123-
Table 87. Carabidae species in the prey of Achaearanea riparia in
a winter wheat field near Zurich (years 1977 and 1979).
1977
Carabidae species
N
3
I
CliviLa fossor
I
I
Acupalpus teutonus
I
Lori cera pi l i corni
Agonum
s
dorsale
Agonum muel
Total
1979
N
4
2
1
1
I
I|
2
2
I
leri
t
il
Amara spec.
spec. ?a
Carabidae gen. spec,a
z
Amara
2
Total
0
0
0
24
21
16.67
8.33
4.17
4.17
4.17
45.83
8.33
8.33
100.0
a 0nly fragments found
of prey items captured by Nuctenea cornuta
per web and per day in a rye field near Zurich-
Table 88. Number
l.leiningen (surmer 1976).
No. webs
Date
Prey/web/day
.
7
12.6
26.6.
8
15.0
28.6.
q
9.2
7
20.0
?5.6
1.7,
ö
8.'l
EA
4
25.0
6.7.
4
10. 3
xjsE
14.3
j
2.3
-124shows that on days without rain, ]4.3 t 2.3* prey items/day on the average
got caught in a web of about 500 cm2 of N. cornuta. In a cereal field,
more than 200 Diptera were found in a singT-iel-i-t N. cornuta. This
indicates that spiders have a high killing potential.
Ground surface
As can be seen in Table 89, about 4% of the wolf spiders, observed in
winter wheat fields jn 1978 and 1979, held a prey betv.,een their
chelicerae. 0f the ground-dwel1ing web-building spiders also, only
about 4% were actually feeding. Adult wolf spiders (P. agrestis) need
about 45-60 min for the consumption of a small prey (Tab1e 67j. These
data being known, the prey capture rate was calculated by means of the
method of EDGAR (1969, 1970), and was found to be less than I prey
item/spider/day
for the
3.3.5.5.
of prey capture days per year
Number
l.licryphantidae and Lycosidae.
Vegetation zone
flying abiljties of
the prey insects, only days without rainfall offer optimal conditions
for the spiders to catch prey. The spider webs not destroyed by wind
and rain capture significantly less prey on rainy days than on rainless
days, even when precipitations are restricted to part of the day
(Mann-Whitney U-test, p <0.01). In the year 1976, only 45 days of the
period which the spiders stayed in the cereal fields were without rainfall, and in 1977 only 36 days. In maize fields, however, 78 and 64
days resp. were rainless duning the time the spiders stayed ther"e in
As rain destroys the spiders'webs and impairs the
'1976 and 1977.
Spiders can thus actively capture prey on 40 days/year
on
the average under most favorable and on 30 days/year under less favorable
conditions in cereal fields, but on 7l days/year or 59 days/year resp.
in
maize
fields.
Ground surface
The ground-dwe11ing spider conrnunity 'is less influenced by combine
harvesting. The ground sunface can therefore be colonized by spiders
during a longer period
of time than the vegetation
zone.
3.3.6. Niche breadth and niche overlap concerning the food of spijlgrs
3.3.6.,l. Vegetation zone
coefficjents Öl of the food overlaps of the web-building spiders coexisting in the vegetation zone of cereal fields are compjled in Table 90.
T[e values show that 12 of the 2l tested overlap pairs are significant
(Cr >0,60)**. The food compositions of the Araneidae show a total overlap,
although each species has a different web pattern (C^ >0.95.'. prey comThe
positions identical). Between the food compositions of Araneidae and
Tgtragnathidae there is also a significant overlap in every case
(CI = 0,68-0.76). The overlaps between Theridion impressum with a space
web, on the one'hand, and thä orb-weavii!'-fi-dersl-on-i*n'-e otner hand, are
Mean t standard error (i ! SE)
**If the overlap had been calculated at species level of the prey instead
of order level, lower ovenlap values would possibly have resulted.
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@!!
9.FO
=9p
ci
o
o
€G
F
Araneus
di adematus
looo--B
t.
l---ooo
6l
.-l
6l d
5l
dl
plddldl6ldl
dlolPl<l.olol
El Ll rl
El .rl
dl
rl
ol Ll
oJ o
€1
31 OI
fl36l
dl
6l
.-l dl ol ol rl
rl ' (l
6l !l
.-l 61
6l
6r ol ol dr cl
ql
oJ cl !l
=l
ol ol ol ol dl
cl
Pl s{ !l
6l -l
ol cl Pl
=l rl dl ol
!l
ol
!l
.-l
c1
.Fl
cl
ol
.-l
!l.rl
!l
ol
cl
6l
ol
cl
6l
Ll
ol
ol
dl
<l
ol
',
<l <l zl =l Fl FI <l
_127not significant for the most part 1ör = O.fs-0.22) because, although
impiessum with its space web filters flying insects out of the aerial
happens that jumping
Flänlton,-lust as the orb-weaving spiders, it often
insects and insects running on plants get caught jn the space webs. The
prey composition of T. impressum shows therefore a considerably wider
range of prey types tfräfühe one of the orb-weaving spiders (niche
breadth, see Table 80). A verification by means of the Mann-t,lhitney
U-test confirms that the niche breadth (concerning food) of the
Thenidiidae is significantly larger than that of the orb-weaving spiders
(p <0.05). It is interesting to note that also the food compositions of
the two Theridiidae T. iqgg!:!m and A. riparia overlap only little
(cr = 0.]). This can-56-d!iälnäd uy TfiE-vEiTlcal isolation of the
catching äreas of the two species. Whereas lr--lrngressum builds its webs
mostly in the upper part of the vegetation zoneiFZereal fields and
builds
ther"eiore capture only insects of the vegetation zone, A. r'iparia
'l5.7 t 0.9 cm
its species-characteristic retreats near the ground (about
above ground) and constructs a tangle web down to the ground' in which
mostly grounä-dwelling arthropods get caught (Carabidae' Staphylinidae'
ants, etc.).
As a consequence of the isolation of the catching areas' there are
practically no overlaps between thg food compositions of A. riparia and
those of the orb-weaving spiders (Cr <0.10).
T.
3.3.6.2.
Ground surjace
the ground-dwelling web-building spiders show large
prey size overlaps, s'ince both spider groups prey primarily on small,
soft-bodied prey organisms.
The wo1f spiders and
3.3.7. Spiders as predator"s of pest insects
and
beneficial insects
As mentioned before, cereal aphids, which can be pests in cereal crops'
have been recorded in the food of ground-dwelling spiders. Unfortunately'
the aphids captured by foliage-dwelling spiders were not determined at
species Ievel. But doubtless there were cereal aphids' too' among the
aphids captured by foliage-dwelling spiders.
0n the other hand, as spiders are polyphagous predators who, to a certain
extent, capture their prey at random out of the existing insect supply'
they kill beneficial as well as neutral arthropods along with econoni-
cally harmful insects.
Foremost of all, beneficial aphidivore insects are occasionally captured
by spiders in cereal fields'
Adult stages of Chrysopa carnea Steph., whose-larvae are well-known aphid
predators, got oTEi-cäugIT in the orb-webs of N. cornuta in cereal
ri.tat.
In ä rye field, ior instance, a populati6i-oFX-Icornuta captur"ed
,I.0
1 0.2 C. cärnea/web/night in the surnmer of 1976. The locally sometimes
high propoiTT6i-iT-Chrysopidae in the food of N. cornuta can probably be
explained by the temporal as well as vertical coincidence between the
flying space of C. carnea and the living space of l!. !9Mlq, for both
späciäs äre active-äT-n'ight or in twilight, and the-Tjfing-Feight of
C. carnea lies in the catching range of N. cornuta webs.
-128_
0ther aphid predators such as Coccinellidae, Canthanidae and Syrphidae
are also occasionally pneyed upon by web-building spider"s in cereal
fields.0n the average, the spiders caught one aphid predator per 6.6
aphids.
3.3.8. Prey killing rate
3.3.8.'l.
Prey
killing rate in the vegetation
zone
The prey killing rate of the foliage-dwelling spiders in cereal fields
was calculated similarly as for the spiders in abandoned grasslands (see
3.l.ll.l.), on the basis of the estimated total web area (Ao). Thjs web
at least all .air-weather days, frorn the datb of
irrnigration into the field until harvest, and filtens the aerial plankton
in the vegetation zone. Hunting spjders, which amount to merely 2-5% of
the total spider fauna, were not included in the calculation.
area exists on
The
yearly prey killing rate P can be calculated by
equati
means
of
the
on
P=A[Nf.Tr) +(Nr.rr)]
where A
is the area of the spider's
webs
in
m2lha ground area
(A = iO-lO0 m2 web area/ha ground area in wheat, iye, and oat fieldsi
A(5 nz web area/ha ground aqea in maize fields); N1 and N. are the
of captured insects/mz web area/day in respectively fair and
rainy weather and T1 and Tr = time as numbers of prey capture days/year
in respectively fair and rainy weather. Nf amounts to about 290 insects/m'^
web area/day in cereal fields (see 3.5.4.i,). 0n1y a fract'ion of N1 was
used for N., as less prey is captured on rainy days. The values for T1
and T" were chosen on the basis of sections2.1. (Tab1e 5) and 3.3.5.5.
The computations produced the followlng values: A yearly number of
insects in the order of 0.2-1.2 x l0o insects/ha (insect biomass:
0.2-1.2 kg fresh weight/ha/year) is filtered out of the aerial plankton
by the foliage-dwelling spider comnunity of wheat, rye, and oat fields.
The foliage-dwelling spider cormunity of maize fields filters a yearly
number of insects in the order of<0.1 x l0o insects/ha out of the
aerial plankton (insect biomass <0.1 kg fresh weight/ha/year).
numbers
It is probable
lower
in rainy
that these values for ceneal
and maize
fields
range far
sunmers.
3.3.8.2. Prey kill'ing rate on the ground surface
In the wolf spiders, the prey killing rate Ps in a winter weat field
was
calculated after the following formula:
P
=to4o c'T
the parameters are: D = density (number of wolf spiders/m2),
= prey capture rate (number of prey items/spider/day), T = time (number
of activity days/year). The following estimate values were used in the
where
C
-129formula: D = 0.5 (see 2.3.2.2.,-below), C = 'l (see 3.3.5.4.), and
T = ]00. Thus P, amounted to l0o D.
0n this basis it could be calculated, that approximately 0.5 x 106 prey
organisms/ha/year are killed by wolf spiders in a winter wheat field. 0n
the assumption that the prey items of the wolf spiders have an average
fresh weight of about l mg, the biomass of the prey amounts to 0.5 kg
fresh weight/ha/year. This is, however, a rough estimate, without
cons'ideration
of the seasonal variations of density and age structure of
the wo'lf spider populations.
The prey killing rate of the ground-dwelling web-building spiders in
cereal fields was not investigated. However, since in cereal fields the
density of the Micryphantidae is about 100 times higher than that of wolf
spiders, the former will probably kill a far larger number of prey items/
ha/year.
3.3.9.
Energy
flow through the spider conünunities
of the prey biomass values (kg fresh weight/ha/year) of
section 3.3.8.1. into energy flow values (l'lJ/ha/year) gave the following
results: The energy flow (= prey killed) through the foliage-dwe11ing
spider conrmunity ranges in the dimension of 1.1-6.5 MJ/ha/year in cereal
fields and <0.5 t'lJ/ha/year in maize fields.
A conversion
3.3 .9 .?.
The dai)y energy flow (= food consumed) through the ground-dwelling
web-building spider guild was estimated by means of the nethod described
in section 2.3.10.2.
The energy flow through the ground-dwelling web-building spider guild of
winter wheat fjelds was calculated to be approximately ll7-524 kJ/ha/day.
This corresponds to l2-52 MJ/ha/100 days.
The computation of the energy flow through the ground-dwelling web-bui1ding spider guild of maize fields resulted in approximately i30-344 kJ/
ha/day. This corresponds to l3-34 l,'lJlha/100 days.
The energy flow through the wolf spider guild of a winter wheat field
was calculated to be approximately 2.4 I'lJ/ha/100 days.
records of remarkable spider species in the region of Zurich
Within the frame of this thesis more than l5'000 spiders were collected.
Because of lack of time, not all of these spiders could be identified.
Among the detennined spiders, some species were found which' so far' had
3.4.
New
exceedingly seldom been recorded
MAURER
& WALTER, 1980)l The
Compare
also
NYFFELER
in
Switzer"land (comp.
MAURER, 1978;
following are the most important discoveries:
& BENZ (1982b)
-
130 -
adult d of Tteridiox boesenbergi Strand was found in an abandoned
uioto[älTfll(Gt. TfiÄtEF, Table 16). This species had
previously very seldom been recorded in Switzerland (DE LESSERT, 1910;
H0LZAPFEL, 1937; MAURER, 1978).,l960;
Ir_!9S:g!SS! is a rare species in
.l937;
general (l^lIEHLE,
THALER, pers. comm.).
BRAUN,
One adult d of Dictyna puella Simon was found in cultjvated meadow C4
(det. THALER, Tä51e 50). As far as is known, this record of the species
in Suritzerland is the only for Central Europe (see also NYFFELER & BENZ'
l98ld). It is a typica.lly Mediterranean species (B0NNET, 1956). D. puella
is reported to have been found also in Western Europe as well as SouthOne
grassland
eastern Europe
(L0CKET & MILLIDGE,
l95l/53;
B0NNET, 1956).
Porrhoma oblitum (0.P.-Cambr.) was found in cultivated
rneadow C5 laet.TFÄ[EFi-raU-Te-5T) . This species had been recorded only
once befor"ä in switzerland (MÜLLER & SCHENKEL, 1895).
One adult I of
Adult specimen of Oedothorax fuscus (Blackw.) were collected in the
cultivated meadows e3 and C4 (det. NYFFELER, Tables 50, 53). Adult dd
of 0. fuscus were also captured in winter wheat fields of the Swiss
FedffiT-Reiearch Station for Agronomy Zurich-Reckenholz. 0' fuscus had'
so far, only very seldom been recorded in Switzerland (MAURER, 1980).
This species is not rare, however, in Europe (LOCKET & MILLIDGE' l95l/53;
t'JIEHLE, l960). It has probably escaped notice in Switzerland before'
because only few pitfall trap studies have been made in this country.
Adult dd of 0edothorax tuberosus (81ackw.) were collected in a winter
wheat f j e I d oT-TEä51Ts-FEäffiT-nesearch S tati on f or Ag ronomy,
Zurich-Reckenholz (det. NYFFELER). This species was captured by means of
The species had seldom been found in Switzer"land before
It is not rare, however, in Europe (LOCKET & l'IILLIDGE,
l95l/53; t.,lIEHLE, 1960).
One adult d of Araneus alsine lJalck' was found in a wheat field near
Regensdorf (detl-frYFFELER'flTt was captured with the sweep net in midAuöust. Thii spider species had not been recorded in Switzerland in the
last 40 years (MAURER, I978).
Four juven'ile Heriaeus spec. were collected in the "Chrähenriet" near
Resenidorf (coöfüTn-ätes 679.05/254.35) (det- NYFFELER). The location is
a rnoorland ecosystem cornplex in a nature preserve. As only ifinature
stages were found, it was not possible to deterrnine the species. Up to
the present, only the species Heriaeus oblongus Simon had been found
pitfall traps.
(MAURER,
1980).
before in Switzerland (MAURER,_1978]. North of the Alpes only one
specimen of H. oblongui had been found so far on Swiss territory
(voerLSANGERTlS3gJ.-!g1ggg: species are rare in Central Europe.
4.
t3t
DISCUSSION
4.1. Colonization of grassland and cergal fields by spiders
The knowledge of population densities is one of the rnost important basic
infonmatjons needed for the evaluation of the ecological importance of
animals in ecosystems. It was therefore of gneat interest to compare the
spider densities determined within the frame of this thesis near Zurich
with the observations from other places stated in the literature.
9l is a comparative representation of the populat'ion densities of
foliage-dwelling spiders in arable land and grassland ecosystems on the
one hand and forest ecosystems on the other hand. The table can be interpreted in the following manner: Spiders living undisturbed in the
vegetation zone of abandoned grasslands al1 year long can reproduce in
accordance with their prey supply and can therefore build up rather large
populations. Abandoned grasslands often constitute veritable "spider
Table
parad'i ses "
.
Cultivated meadows, on the other hand, are periodically mown, whereby the
living spaces and the egg sacs of many spiders are destroyed. For that
reason, only small spider populations (about 1 spider/mz) l'ive in the
vegetation zone of cultivated neadows. Although there is a controversy in
the literature still today, as to whether or not mowing is an ecological
disaster for the foliage-dwelling fauna (see
B0NESS,
I953; KAJAK,
.l968;
'l962;
,l973;
SCHAEFER,
CHAUVIN,1967; S0UTH[^100D & VAN EMDEN,1967; M0RRIS,
SCHAEFER & HMS, 1979t NYFFELER & BENZ, 1979b),ourdata show that mowing'
at least in the region of Zurich, is an "ecological disaster" for the
sp'iders of the vegetation zone of meadows.
for the foliage-dwelling spiders of cereal fields, the harvest is
of the living space and the egg sacs of
many spiders). Therefore, a recolonization of the fields from the
surroundings is necessary every year (see also TISCHLER, I958; GEILER,
'1963; LUCZAK, 1979). As cereal fields are annual monocultures, which
Also
an extreme stress (destruction
allow only few different ecological niches, they can probably be
colonized only by a few species, whose ecological demands are adapted
to the microclimatic conditions and the vertical structure of cereal
fields. The species composition of the spiders of cereal fields represents
therefore a selection of the spiders living in the neighbouring
undisturbed biotopes. The colonization of the fields, on the one hand, is
dependent on the relation of the area of undisturbed biotopes (the so
cal1ed ecological cells or "ökologische Zellen" of the German literature)
to the area of cultivated land jn the landscape and, on the other hand,
on the species compositions, population densities, and reproduction rates
of the spiders living in these ecological cells (i.e. less disturbed
habitats and biotopes, like unmown stripes of grassland, woods, hedges,
reeds, gardens, etc.). 0n the outskir"ts of Zurich, the fields are nostly
surrounded by only few small undisturbed biotopes (unmown stripes of
grassland, forest fringes, hedges), wherefrom the spiders can colonize the
vegetation zone of the fields. As the area of these biotopes, untouched
by agriculture, is probably too smail to produce cereal-dwelling spiders
in numbers so large that hundreds of thousands of them could emigrate'
many fields are only thinly colonized. The colonization of annual cnops
-132-
of the densities of the foliage-dwe11ing spiders as reported in literature for agroecosystems, grassland ecosystems and forest
ecosystems. The different data have been collected by means of different methods and under different circumstances. The table therefore
can give only a rough comparison.
Table 9.l. Comparison
LOUnf,ry
Crop
Dens
i tv
Autnor
N/n'
Intensively cultivated:
Cerea'ls
Switzerland
Rye
Pol and
0.,l0.6-
0.6
7.0
2.2
small
Mai ze
Switzerland <0.1- 0.'l
Potato
Switzerland <].0- 5.0
Potato
Pol and
0.6-29.6
Rape
Switzerland 0.'l- 0.5
Cotton
U. S. A.
0.8
Coffeea
New Guinea
6.6
Al fal fa
PoI and
2.2- 3.6
Cultivatedmeadow Poland
0.6- 4.4
Barl ey
Pol and
0ats
Fi nl and
Extensi
uncul
NYFFELER
& BENZ (1979a)
LUCZAK (1975)
LUCZAK (197s)
& HUHTA (]968)
& BENZ (1979a)
RAATIKAINEN
NYFFELER
& BENZ (]979a)
LUCZAK (r975)
NYFFELER
NYFFELER
& BENZ (1979a)
WHITCOMB
et al.
RoBINSoN
& RoBINSoN (]974)
(1963b)
LUCZAK (1975)
KAJAK
et al.
(1971)
vely cul ti vated/
ti vated:
Britain 842.0
Britain 559.6
Grass I and
Pol and
52.C
Overgrazed pastureb Canada
44.0
Grass I andb
U. S. A.
56.0
25.0
Tulip poplar forest U.S.A.
Deciduous forest
U.S.A.
5r.0
Pine forest
Poland
r8.8-33.0
Poland
22.0-31.2
Mixed forest
Grass I andb
Great
DUFFEY (1962)
Grass I andb
Great
BRISToWE (1939)
KAJAK
et ai.
(.1971)
TURNBULL (1966)
VAN H00K
REICHLE
(t971)
&
CRoSSLEY (1967)
PECK (1966)
LUCZAK(1975)
LUCZAK (1975)
a 0nly web-building spiders
b All strata including ground surface; in some grassland types a clear separation of the spider fauna of the vegetation zone and of the ground surface is
not possible, as in such grasslands many ground-dwelling spidens hunt also in
the vegetati on zone
Table 92. Comparison
133 -
of the densities of ground-dwelling spiders as reported in
ljterature for
uncultivated grassland ecosystens
agroecosystems,
forest ecosystems. 0therways as Table
Ecosys tem
Country
Spi
and
91,
ders/m2 Author
Agroecosystems:
fielda
fieldb
Winter wheat fieldc
Cereal and beet fieldsd
Cereal field
Cultivated rneadow
Cultivated meadowe
Cultivated meadow
Cultivated rneador{
Pasturef
Winter wheat
Maize
Switzerland 12- 53
Switzerland 13- 35
19
Germany
Germany
250
Great Britain 20- 30
Austria
54
Great Britain
35
Poland
l0- 14
Poland
74
Panama
37
Undisturbed grassl and ecosystems
NYFFELER
& BENZ (1979a)
NYFFELER
& BENZ (]979a)
BASED0W (.1973)
HEYDEMANN
(1962)
FRASER
(1982)
THALER
et al.
(1978)
DUFFEY (1974)
KAJAK
et al.
(1971)
KAJAK & JAKUBCZYK (1975)
BREYMEYER
(1978)
:
grassland
Austria
grassland9 Great Britain
grassland
Poland
pastureh
0vergrazed
Canada
Uncult.
Uncult.
Uncult.
53-
37
62
45
44
THALER
et al.
DUFFEY
(1974)
KAJAK
et al.
(1978)
(.1971 )
TURNBULL (1966)
Forest ecosystems:
forest
forest
Chestnut forest
0ak-beech forest
Beech forest
Oak forest
Pine-spruce forest
Pine forest
Tulip poplar forest
Spruce
Alder
Gennany
6l
Austria
5l
France
75
Great Britain l5-ll0
Netherland 163-231
Denmark
Sweden
Finland
U.S.A.
60
240
183
126
PFETTEN (1925)
THALER
et al.
CHRIST0PHE
(1978)
& BLANDIN (1977)
GABBUTT ( 1956)
VAN DER DRIFT (195.l)
B0RNEBUSCH (1930)
F0RSSLUND
HUHTA
(1943, 1945)
(1971)
MOULDER
& REICHLE (1972)
a In May/June, without Lycosidae. b June/July, without Lycosidae. c In July.
d 0nly 0.dotho"u* apicatus. e Including spiders of the i2 cm high vegetation.
f In August/September. 9 Including spiders of the 25 cm high vegetation.
h Including spiders of the vegetation zone (comp. Table 9l).
-
134 -
initial stage of a succession. According to
(1968), in Finland, too, only 1ow spider densities
the vegetation zone of oat fields.
never trespasses the
RAATIKAINEN & HUHTA
were observed
If
in
we consider
the ground surface, however, we notjce that there the
live in rather large popuiations, not only in natural ecosystems
but also in agroecosystems (Tab1e 92). In cultivated fiqlds near
zurich, densilies of up to 53 groundldwelling spiders/m2 were observed,
and this number includes merely the spiders found on the ground surface.
But in cultivated fields, there are also spiders which Iive in cracks of
the soil. If soil extractions had been examiqed by means of Berlese
spiders
funnels, even more ground-dwelling spiders/mz might have been found, In
the German Democratic Republic, too, GEILER (1963) observed that the
greater part of the spiders in crop fields lived near the ground. The
relatively high spider density near the ground can be explained by the
fact that crop fields never get beyond the initial stage of a succession
and that, therefore, the area near the ground is for the most part
colonized by pioneer species which have a high reproductive potential
(r-strategists, e.g. Erigone atra).
The influence of soil cultivation (e.g. ti lling, fertilizing) on the
ground-dwelling spider populations of agroecosystems couid not be
investigated within the framework
of this thesis. Informations
from
literature indicate, however, that soil cultivations does influence the
composition of ground-dwelling spider cormunitjes (TISCHLER, 1965;
LUCZAK,
1975; KAJAK, 1978, 1980).
and species conposition of the spiders
multitude of spider species of the families Araneidae, Tetragnathidae,
Theni di idae, Li nyphi i dae, Mi cryphanti dae, Agel enidae, Di ctyn'idae,
4.2. Family
A
Salticidae, Thomisidae, Pisauridae,
and Clubionidae can be found
of abandoned grasslands.
In contrast to this, only a limited number of
in
the
vegetation zone
first
four famil ies and the
vegetation zone
predominant species
Thomisidae can be observed
of cultivated
meadows and
of
the
regularly in the
cereal fields.
Large orb-weaving spiders (4IE_SPg bruennichi, Araneus quadratus) and
funnel web spiders (Agelena labyrinthica, Agelena similis), whjch are
found in high densitie! jn abandoned grasslands, are almost entirely
missing in cultivated fields. Also, "i'Jmping spiders (Evarcha alcuata,
Heliophanus flavipes) and pisaurid spiders (Pisaura mirabilis), which
praaominate ln the vegetation of abandoned grasslands, are found in
exceedingly low densities in cultivated fields. These differences
between the spider faunas of undisturbed and cultivated biotopes can be
explained by the fact that by cultivating the land (tilling, mowing'
single-crop farrning, pesticides etc, ) biotopes are created, wherein only
those spiders can exist whose demands are met even in these "artificial
envi ronments "
.
Also the spider fauna of the vegetation zone of cereal fields in the
region of Zurich is composed of mainly web-building spjders (95-98%) of
the families Araneidae, Tetragnathidae, Theridiidae, and Linyphiidae. In
contrast to meadows, however, hunting spiders of the family Thomisidae
_ 135
_
were only seldom observed in the fields. Similar observations were
by LUCZAK (1974) for potato and rye fields in Poland.
made
of the species composition of the spiders in the vegetation
of cultivated fields in Switzerland, the Federai Republic of Gennany,
A comparison
zone
Finland, The German Democratic Republic, Norway, and poland shows
(DINGLER, 1935; GEILER, 'l963; TISCHLER, 1965;
GALECKA, 'l966; RAATIKAINEN & HUHTA, 'l968; TAKSDAL, 1973i HUHTA &
RAATIKAINEN, 1974; LUCZAK, 1974, 1975, 1976; CZAJKA & G00S, 1975;
.l976;
certain conformity
a
& KANIA,
NYFFELER & BENZ, 1979a). Theridiidae (Theridion
impressum, Enoplognatha ovata), Linyphiidae (several specie;T;Tetragnathidae (Tgtrggnatha extensa, Tetragnatha pinicola), Araneidae
(Araniel la spp., &q!leperra ceropegia, Nuctenea cornuta, Mangora acalypha)
CZAJKA
as weTlf,T rnomi
sl?äälTFTt@-iffi
preäotTnätEä-.
The ground-dwelling spider fauna of the investigated fields near Zurich
.l977-1979
was unifonm and was dominated in
by the Lycosidae pardosa
palustlj: and Pardgsa-agrestis, as well as the Micryphantidae-(@1g
atra, Erjgone
arra,
Lrrgone dentrpatpls,
dentipalpis, and 0edothorax
oedothorax spp.).4
spp.). A litile less Trequent
frequent
were the Tetragnathidae (Pachygnatha spp.) and Linyphiidae (several
little
species). This species compositibn 1n the investigated fields largely
corresponds with the situation in field crops of Austria, England, the
Federal Republic of Germany, the German Democratic Republic, and poland
(see TISCHLER, I965; LUCZAK, I974i VICKERMAN &
& G00S, '1976; THALER et al., 1977).
SUNDERLAND,
I975,
CZAJKA
l.lith the exception of Dictyna puella, the spider species descr"ibed in
this study have
all
been previously r"ecorded in Switzerland (see MAURER,
& I^/ALTER, 1980). Although agroecosystems are very monotonous
systems with few djfferent ecological niches, some rare spider species
were discovered in them (e.9. Porrhonma oblitum). The terrn',rare spider
species" is however relative, ä1, uF to the pr"esent, only few
arachnologists have conducted faunistic studjes in Switzerland. These
rare species probably are not true components of the spider conrnunities
of agroecosystems, but rather inhabitants by mistake.
1978;
MAURER
4.3. Spatial distribution of spiders
4.3.1. Vertical distribution of spiders
In the vegetation zone of abandoned grassland near Zurich a vertical
stratification in orb web-building spiders could be ascertained (see
also
& BENZ, 1978), Similar observations v.,ere reported by pASQUET &
KRAFFT (1980) in an old prairie in France. American investigations in
uncultivated grassland also have shown
.l974;vertical stratification in
NYFFELER
orb web-building spiders
BRoWN,
l98t).
(ENDERS,
UETZ
et
al.,
I978;0LIVE,
In cereal fields near Zurich spiders were found from the
1980;
ground surface
to the ear zone, whereby some spiden species Iife more near ground,
other ones more in the middle or hjgher stratuns of the vegetation. In
other countries, too, it could be noticed that spiders in cultivated
fields are present fnom the ground surface up to the ear zone, whereby
in some cases vertical stratification of the spiders was observed
(WHITC0MB et al.,,l963b;BAILEY & CHADA, 'l968; OKUMA & WONGSIRI, 'l973;
up
LESAR
& UNZICKER, 1978a).
'l36 -
4.3.2. Horizontal distribution of
s i
ders
cereal fields near Zurich the horizontal
distrjbution of the foliage-dwelling spiders corresponded with a random
distribution, in abandoned grassland with a random or slightly aggregated distribution. The same is true for the horizontal distribution of
the ground-dwelling spiders in cultivated meadows and cereal fields near
In cultivated
meadows and
Zuri ch,
A comparison w'ith the data of literature shows, that also jn other ecosystens the spiders are distributed at random and/or aggregated, whereby
the aggregated distribution seems to dominate (see CHERRETT, 1964;,l974b;
TURNBULL, 1966; HUHTA, 197]i PIETERS & STERLING, 1974; SCHAEFER,
DIPPENAAR-SCHOEMANN, 1976; CHRIST0PHE & BLANDIN, 1977; BISH0P, 1981).
Reports on a nearly regular distribution of spiders are rare (RIECHERT
et al.,.l973;
SUZUKI & 0KUMA,1975; ES'KOV,1981).
4.3.3. Distribution of spiders
among
the outer, middle and inner parts
tn . ,iililIäfll-"ar
zurich the sround-dwelling spiders were
equally distributed in the outer, middle and inner parts. The same has
been reported from an Australian cotton field, where dominant spider
species were equally distributed, too (BISHOP,1981).0n the other hand,
an investigation of D0ANE & DONDALE ('l979) in Canada showed that
significant fewer spiders were captured per pitfall trap in a
wheatfieldthan in its grassy borders.
4.4, Prey conpositions
If we consider the food composition of the spiders relating to the number
of captured prey items in the vegetation zone of grassland, cereal fields
and other biotopes, it is evident that small Diptera form the main part
in the food of orb-weaving spiders (Table 93). Moreover, winged aphids
are also an important component of the food of these spiders. Diptera
and aphids also predominate in the food of many space web spiders in the
vegetation of grasslands and cereal fields,
Numerous other authors have also observed that Diptera predominate in
number in the prey of most foliage-dwelling web spiders of cultivated
(DINGLER, 1935; TURNBULL, 1960; WHITCOMB et al.,
and uncultivated areas.l964:
'l968; l,{HEELER' 1973;
PUTMAN, 1967; HARRISON,
1963b; RUPPERTSH0FEN,
MUMA,,l975; SUZUKI & OKUMA,1975i ROGERS & H0RNER,1977; NENTWIG,1980,
l98l). That small Diptera constitute such an essential part in the food
of the foliage-dwelling spiders, is due to the fact that - in number Diptera form the main part of the insects in the vegetation zone of
grasslands (BONESS, 1953; PERTERER & THALER' 1976)' field crops (DINGLER'
.l935;
PRILOP,-l957; KARG & DABROWSKA, 1974), and the aerial plankton'in
general (cEILER, 1975). As the web-building spiders, to a certain extent,
filter their prey out of the aerial plankton, the small Diptera which are
the first in frequency fall victims first. The same js true for winged
at certain times of the year (see KAJAK, 1965a, b; NYFFELER &
aphids
BENZ, 1979a).
If
one considers
the spiders' prey composition wjth respect to bjomass'
of the spiders living in the vegetatjon
one sees that here, too, the food
-137-
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cereal fields consists of Diptera mainly.
of abandoned grasslands, on the other
hand, the situation is different. The food of A. bruennichi, for jnstance,
zone
of cultivated
_
meadows and
For the large web-building spiders
consists mostly
of 1arge, heavy
of
in
honey-bees ana-ffisshopp'äis. Up
to
the
present, this spider species was considered to be primarily a predator
,I943;
grasshoppers
Europe (V{IEHLE,193I; MARPLES,'|935; FISCHER,
CHAUVIN,1979; LOHMEYER
CR0ME & CRoME, 196l; PÖTZSCH, 1963; CANARD &
-l980).
PRETSCHER, I9T9; GILLANDT & MARTENS,
this feeding behaviour
in the region of Zurich,
&
was observed mainly in abandoned grasslands
and few flowering plants
with a high percentage of grasses
(NYFFELER & BENZ, 1978). Besides grasshoppers, also dragonflies,
Megaloptera, Lepidoptera and ants were described in the literature as
Ppimary prey of A. bruennichj (FISCHER, 1943i CROME & CR0ME, l96l;
PöTZSCH,
lSOe).
ü-ioiTElTTo these former studies, several locations
near Zurich were found, where grasshoppers were almost entirely missing
in the food of A. bruennichi (Tables 2l-28). In abandoned grasslands with
ä high percenta@_T@ arvense and/oi Rubus sp., Aj bruennichi was
observed to perfonn as an outright bee-killer (NYFFELER & BENZ, 1978).
The prey composition
specifjci for, in
of this spider species seems to
be largely genus-
grasslands, grasshoppers (Acrididae) and
also bees are mentioned as main food of the mediterranean Argiope lobata
(Pallas) and the Arnerican A. trifasciata (Forskal), A. aurantia Lucas,
and A. argentata (Fab.) (BILSING, 1920i RICHTER, 1960; RoBINS0N &
abandoned
RoBINSoN, 1970).
l,rlith respect to biomass, the prey of A. quadratus of abandoned grassland
biotopes near Zurich also consjsted mostly of bees (NYFFELER & BENZ,
1978). The same was noticed by BILSING (1920) in abandoned grasslands in
Ohio for the closely related species Araneus trifolium (Hentz).
of the funnel web spider A. labyrinthica in abandoned grasslands
is very rich and mainly composed of grasshoppers, honey-bees,
ants, Lepidoptera, Coleoptera, and Diptera, both with regard to the
number of captured prey as well as biomass. According to BILSING (1920)
and RIECHERT & TRACY (,l975), the same is true for the American funnel
The food
near Zurich
web spidens Agelena naevia lialckenaer and Agelenopsis aperta (Gertsch).
quite different prey compositions of the three large web-building
spiders 4._!fCg11j_ghj-, A. quadratus, and A. labyrinthica even within the
same biotope shows that the vertical isoiation of the webs and their
construct.ion has a great influence on which insects are captured,
Fi9. 19 shows the vertical distribution of the webs of the three spider
species and the selection of prey types resulting from it (NYFFELER &
BENZ, 'l978). The two Araneidae A. bruennichj and A. quadratus build
orb-webs, bu t are verti ca I y i s6Tä'Gä-TFöt-äach oTIEFlÄlquTralgg bu i I ds
its webs in the higher strata of the vegetation (orb hub >0.5 m above
ground, on the average) and captures almost exclusively flying insects,
mostly Diptera and bees. A. bruennichi, on the other hand, builds its
websnearthe ground (orn truU-on TireTTerage <0.35 m above ground) and
captures for that reason also jumping insects such as grasshoppers. Its
pney composition is therefore widen than the one of A. quadratus. The
funnel web spider A. labyrinthica, uses an entireiy different hunting
strategy, since the funnel webs serve to catch both, flying insects as
The
1
139
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-140well as jumping and running arthropods. Its prey composition is therefore significantly wider than that of the tv,/o orb-weaving spiders.
of the ground-dwelling spiders in cultivated
The food
fields
meadows and cereal
near Zurich was primarily composed of small, soft-bodied insects
(mostly Collembola, aphids, Diptera). Up to the present, ground-dwelling
spiders have generally been known from Iiterature to be predators of
.l968i
'l970i
Collembola (BUCHE,.1966; SIMoN, 1967i CLARKE & GRANT,
EDGAR,
.l973i
HALLANDER, 1970; HAGVAR, I973; t,lINGERDEN,
SCHAEFER, 1974a;, SALINAS
& RAR0S, 1975i IIANLEY et al., 1976t GETTMANN, 1978; NYFFELER & BENZ,
I979b). However, their-ioTe as predators of Diptera and aphids has also
been recognized earlier (BASED0!I, I973; DE CLERCQ,1977).
Funther discussions of the feeding ecology of spiders in agroecosystems
can be found in NYFFELER & BENZ (.l978, '1979a, l981a,c).
The spiders' effectiveness as predators of agricultufal pests
Insects belonging to the agriculturally important fam'ilies Pentatomidae
(Heteroptera), El ateridae, Chrysomel idae, Scarabaeidae, Curcul ionidae,
Nitidul idae (Coleoptera), Noctuidae, Pyralidae (Lepidoptera), and
Tipulidae (Diptera) are also found in the prey of the spiders living in
ceneal fields, but amount to such a low percentage of the entire spider
food (Tables 79-80) that the spiders are probably ineffective as predators of the cereal pests belonging to these families.
According to NYFFELER & BENZ (1979a), the populations of the nitidulid
beetle Meligethes aeneus Fbr. were only iittle influenced by the spiders
in the vegetation zone of rape fie'lds.
The same conclusion has been drawn by the Polish ecologist KAJAK (1971)
who found that spiders exert merely a negligible influence on the
mortality of the insect populations in the vegetation zone of cultivated
4.5.
meadows,
tdhether spiders are effective as predators of aphids on cultivated land
in Europe cannot be answered conclusively yeti for in spite of repeated
investigations on spiders as aphid predators, there are still no
quantitative informations on the influence of the spiders on aph'id
mortality
(DUNN, 1949; GALECKA, 1966; SUTER & KELLER, 'l977).
Investigations in the U.S.A. have also
of pest insects in cultivated land
l96li
et al.,
shown
that spiders are predators
(SCHLINGER
& DIETRICK,1960;
CLARK
WHITC0MB
l963bi D0RRIS,1970t McDANIEL & STERLING,
WHITCOMB (1974) c6-nsl7-ers the spiders
North American agroeco-
GLICK,
&
.l979).
of
highly benefic'ial. In a personal comunication he stresses especially the effectiveness of the cursorial spiders (oxyopids, salticids,
gnaphosids, and lycosids). However, there are no quantitative data published as yet on how far spiders influence the population dynamics of pests
in the U.S.A.
systems as
4.6, Spiders as predators of beneficjal insects
A certain percentage of economically beneficial insects was regularly
found in the prey compositions of the foliage-dwelling spiders of cereal
fields. Aphidivore insects (Chrysopidae, Coccinel I jdae, Syrphidae), and
poll'inating insects (bees) are rather frequently captured by spiders.
- l4t Spiders have been repeatedly reported
insects (LOVELL' l9l5; BILSING,'l920i
.l978,
l^IHITCOMB,
1974;
MORSE,
in literature to capture beneficial
1935; KIRCHNER,'l964;
DINGLER'
.198])'
1979; TEMERAK,
aspanagus field that the most
(1935) observed
.important asparagus-dwe1 1 ing spi der species, Thefi dion impressum'
captured mainly economical 1y benefici al insects (Asi 1 idae' Tachini dae'
Api dae, Ichneumoni dae, Sphegidae, Cocci nel I idae' Chrysopidae). He
therefore assumed that the most frequent spider of the asparagus field
was not at all useful, but rather harmful.
As mentioned before WHITCOI4B (1974) discussing the importance of spiders
as regulators of insect populations in American agroecosystems, considers
spiders on the whole as highiy beneficial, but came, among othens, also to
the conclusion: "Since spiders tend to be general feeders, they are natural enemies of most benefic'ial insects. The orb-weavers' ther.idiids' and
other spiders destroy large numbers of parasitoids and pnedators".
DINGLER
in a German
predators destroy
up, one can note that spiders as polyphagous
.likewise.
As wjth many other
"pests", "neutral", and "beneficial" insects
To sum
predators (e.g. birds), whose prey compositions are composed both of
"beneficial" and "pest" species, it is sometimes very difficult with
spiders to determine quantitatively whether in the end the beneficial
effects (destruction of pest insects) or the detrimental effects
(destruction of beneficial arthropods) prevail.
flow through the spider conrnunities
flow thr"ough the foliage-dwelling spider communities of different ecosyitems is compared in Table 94. The table shows the following:
Because the fields are colonized only during a short period of tjme and
because the spider densities are low, the energy flow through the
fol iage-dwelling spider conrnunjties of European cultivated land (cu1tivated meadows and cereal, rape, and potato fjelds) is very 1ow (prey
killjng rate: 0.1-2.0 kg fresh weight/ha/year). In comparison the
production of Diptera alone amounts to about l5 kg fresh weight/ha/year
in rye fields, and to about 20 kg fresh weight/ha/yearin potato fields
4.7.
Energy
The energy
in
Poland (DABR0IISKA-PR0T & KARG, 1974).
In contrast to cultivated fields, spiders can colonize uncultivated
grassland and forest ecosystems all year long in high densities. The
önergy flow through the foliage-dwelling spider cormunities of such ecosystÄms is therefore high. The prey killing rate is 50-200 kg fresh
weiqht/halyear. The energy flow reaches similar values in these biotopes
as lhe energy flow through the fol iage-dwel1ing web-building spider
community oi a tropical coffee plantation, where ROBINS0N & R0BINS0N
(1974) have observed a prey killing rate of 160 kg fresh weight/ha/year'
An intermediate system between cultivated fie'lds and uncultivated grassland may be represented by the Phraqnites belt of some European lakes.
Since these reeds are nown once in a year, their spider populations
are reduced, though less than in cultivated f.ields. As Table 94 shotrrs'
the energy flow through the spider corffnunity in the reed belt of an
European lake corresponded to 5 kg fresh weight/ha/year on the
average, with a maximum of l2 kg/ha/year.
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-
143 -
Table 95. Energy flow (= food ingested) through the ground-dwell'ing spider
of different
communities
Ecosystem
ecosystems.
country
l.linter wheat fieldab Switzerland
Maize
fielda
Winter wheat
Rye
fieldc
fieldc
Cultivated meadowb
Cul
ti
vated
meadowe
Uncult. grasslande
Tulip poplar forestf
Switzerland
Switzerland
Poland
Switzerland
Pol and
Poland
U.S.A.
Energy
kJ .ha-
1
f]
ow-
.duy- I
'li7- 524
130- 344
24d
40
I55- 419
I 070
3360
]40- 330
Authors
this thesis
this thesis
this thesis
LUCZAK
this
KAJAK
KAJAK
et al .
et al.
( I 971 )
(]97.1)
MOULDER
&
a-ln
(]975)
thesis
RETCHLE ( 1972)
June
b llithout Lycosidae
c 0nly
Lycosidae
d This value has been calculated by dividing the prey killing rate of section 3.3.9.2. by l.25 (see method 2.3.11.2.)
e l4g1^21y"ar were converted into approxinate values of kJ/ha/day, by dividing the annual energy flow by 180 days
f Minirrr in winter,
maximum
in
spring
_ 144 _
The energy flow through the ground-dwelling spider conmunities of
different ecosystems is compared in Table 95. The table shows that the
energy flow through the gnound-dwe11ing spider communities of Central
European wheat and maize fieids corresponds, in the order of magnitude'
to the energy flow through the spider community on the floor of an
Arnerican tulip tree forest. In contrast to this, the energy flows through
the gnound-dwe11ing spider conmunities of Poljsh meadows showed signifi-
cantly higher values.
4.8. Numerical
and
AA*rT-
functional responses of
To evaluate the role of spiders as regulators of insect populations in
the agricultural biocenose, it is important to know whether spiders react
to fluctuations in density of their prey populations
(RIECHERT' 1974;
1979). In our case, we have predator-prey systems with the
'l966) there are two
spiders as pnedators. According to HOLLING (1961,
different possibilities for a predator to demonstrate a density-dependent
response to changes in prey abundance:
(l) The predator reacts to an increase in the prey density by capturing
more prey (functional response).
(2) The predator follows an increase in the prey density by increasing
its own reproduction (numerical response).
Under laboratory conditions, both a "functional response" of spiders 'l980a;
LUCZAK,
(HAYNES & SISOJEVIC, 1966; HARDMAN & TURNBULL, 1974; MANS0UR g! al.'
as well as a "numerical response" of spiders (I,JISE,1979i a.o.) has been
demonstr"ated. Laboratory ecosystems, however, are greatly simpl ified
systems. One cannot positively conclude from laboratory experiments that
spiders will show the same behaviour in open-field ecosystems' which are
essentially more complex in structure.
The question is, whether functional and numerical responses of the spi.ders
to density changes of their prey populations are possible in abandoned
grasslands. As these areas are not cultivated, the spider populations
änd the.ir egg sacs are not destroyed by agricultural treatments, as is
regularly the case in cultivated meadows and cereal fields. Functional
of the spiders to density changes of the prey
popuiations should therefore be possible in such biotopes' One can.thus
assume that the spiders in abandoned grasslands reproduce in accordance
with the prey supply, i.e. that they adapt themselves to the prey
densjty numerically. However, although a regulatory activity of the
and numerical responses
js conceivable' it has to be proven yet'
What about functional and numerical responses of the spiders to density
changes of the prey populations in cultivated meadows and cereal fields?
A functional response by the spiders in cultivated meadows and cereal
fields is possible according to KAJAK ('l965a) andNYFFELER & BENZ (1979a).
A numerical response, however, is probablyseverelyhandicaped in
cu'ltivated meadows and cereal fields, because by the mowing and
harvesting of the vegetation zone many egg sacs are destroyed. A
regulatory activity by the spiders in the vegetation zone of such agroecösystemi is therefore highly improbable' Whether or not a regulatory
activity of spiders on the ground surface is taking place' has not yet
spiders in abandoned grasslands
been examined.
a.o.)
r
- ]45 4.9. E:ological inportance of the spiders jn grassland
and cereal
ecosys tems
Spiders can be of ecological importance in diverse respects. For example
the spider
they can be food for other predators (I,IHITCOMB, l974). 0r.l975;
webs can be food sources for kleptoparasites (THORNHILL'
NYFFELER & BENZ, 1980b).In this sectjon, only the role of spiders as
insect predators will be discussed.
ecological importance of spiders is to be expected in abandoned grasslands foiemost, where they can feed and reproduce in the vegetation
without human interference. As already mentioned, such biotopes often
represent veritable "spider paradises". Large funnel web spiders and
orb-weaving spiders often live in high densities in abandoned grasslands'
l,llith their strong webs they capture large amounts of insects.
A. bruennjchi, e.g. may capture up to 7 grasshoppers/web/day.. L0HMEYER
tTIETSeHmTlgTg) found on the average 6 webs of A. bruennichi. per mz
in an abandoned giassland in the Fe(eral Republic of Genmany. This
corresponds to a web area of 30OO m2lha ground area. It is evjdent that
such a gigantic web area exerts an enonnous predatory pressure on'insect
An
popul ati ons
.
Polish studies have also shown that the orb-weaving spiders can exert
strong predatory pressure on the insect populations
.l968; in the vegetation
a
KAJAK & OLECH0WICZ'
öf abandoned grasslands (KAJAK et al.,
1970i KAJAK, 1971). Thus web-building spiders eliminated 25-40% of the
adult Diptera in undisturbed grasslands (KAJAK & OLECHOWICZ' I970).
zone
Funnel web spiders
(A. labyrinthica)
can
also occulin-high densitiesrin
undisturbed grasslanAa-X;äJ' zurl;F, more than 3 funnel web spiders/mz
on the average were counted in some abandoned grassland biotopes' At
certain poinls of aggregation withjn such a biotope, up to l2 funnel web
spiders/rn2 were found. The food of these spiders was composed of up to
23% of bees (NYFFELER & BENZ, 1978). In other countries, too, it has been
observed thai funnel web spiders cän be predators of bees. OLBERG (.1960)
wrote on this subiect: "Sometimes,20 to 30 captured honey-bees on the
average can be found in each web; thus with a spider that frequent' a
consjäer"able damage can result. This is why flocks of sheep are driven
through the dangeied areas. The fleecy animals destroy the webs, which
cunnol be repla;ed imrnediately, as is the case in orb weaving-spiders"'
This example demonstrates that spiders can have a noticeable effect on
i nsect popul ations .
Hunting spiders, too, can play an important ecological role in abandoned
grasslands (VAN H00K, l97l; SCHAEFER' 1974a)'
In contrast to the conditions in uncultivated biotopes' the present
results show that the energy flow through the foliage-dwelling spider
cornmunities of cultivated meadows and annual crops is 1ow (see also
KAJAK, l97li, LUCZAK, 1975). Moreover, spiders are ineffective as predators of rnany agriculturaliy important pest insects (see also DINGLER'
'l935; KAJAK, töZt;. rneretäre, the spiders of the vegetation zone of
Cential Eut"opean äultivated fields probably play no important role as
predators or regulators of pest insects.
The agroecosystems in southern Europe are to some extent cultivated in
a coniiderabiy more extensive way than in Central Europe' It is there-
-146fore conceivable that the spiders still
have a greater
ecological impor-
in cultivated fields of Southern Europe than in the region of
Zurich. Thus, near Florence (Italy), rather high spider densit.ies were
found in the vegetation zone of a weedy cereal field (STREULI, pers.
tance
comm.
).
In contrast to the vegetation zone, the spiders living on the ground
surface of cultivated meadows and cereal fields showed relatively high
population densities (r-strategists, see 4..l.). Together with the
carni vorous beetl es ( Carabi dae and Staphyl i ni dae ) , they bel ong to the
most frequent ground-dwelling predators of insects in cereal fields near
Zurich. German studjes had also established that spjders form an imporground-dwel1ing predator-complex (TISCHLER'
tant
,l958,component within the
1965, GEILER, 1963l' BASED0w, 'l973; BRASSE, 1975; BASEDOW &
MIELKE,1977). In the German Democrati€ Republic, one has even recorded
that spiders and harvestmen can form up to one third of all invertebrates captured in pitfall traps (GEILER, 1963). The prey compositions
of the ground-dwelling spiders overlap to some extent with those of the
predatory Carabidae and Staphylinidae, which also feed on Collembola'
aphids, and Diptera. Further investigations will be necessary to
establish whether this ground-dwelling predator-complex has a significant influence on pest insects (e.g. aphids). First studies already
'indicate that the ground-dwe1ling predator potential actually exerts a
strong predatory pressure on insect populations (BASEDoW, I973i KAJAK &
In any event! this ground-dwelling
stabilizing effect on insect populations'
JAKUBCZIK, 1975; DE CLERCQ,1979).
predator-complex probably has a
as assumed by the American ecologist RIECHERT (.l974).
Studies from Japan, India, China, Taiwan, Korea' Thailand' and the
Philippines indicate that such ground-dwelling spiders, because of their
population
high density in rice fields*, have a damping influence on the
of pest insects, mainiy cicadas (lT0 et a]., 1962;OKUMA, 'l968; IRRI
Annual Report, 1973; CHIU e! qL., 1974; GAVARRA & RAR0S, 1975i
KIRITANI & KAKIYA, 1975; SÄfrAf-& MISRA, 1975;
HOKYO
Ct AI.,]976;
1979T'Tice fields are
swamp ecosystems. In European swamp ecosystems, spiders can also be an
important group of predators (!4ILLER & 0BRTEL, 1975). The same is
assumed concerning the ecological role of spiders in Anerican swamp
NAKASUJI, 1976; KANG & KIRITANI, 1978; KIRITANI,
ecosystems (GARCIA & SCHLINGER, 1972).
4.,l0. Ecological importance of spiders in forest ecosystems and orchards
to the studied gramineae biotopes, some tnee ecosystems
will be briefly discussed.** t,Jith regard to forest ecosystems' the German
ecologist TIEIDEMANN (1978) attributes an important role to the grounddwelling spiders as inseit predators, together with the other litterdwelling predators, A,rnerican scientists, too, concluded that the grounddwelling spiders can be of great importance as jnsect predators in forests
As a comparison
(CLARKE & GRANT, 1968; MOULDER & REICHLE, 1972; MANLEY e! a]., 1976).
in contrast to this, the ecological importance of the fo]iage-dwelling
spiders of forest ecosystems is still controversial (VITE' 1953;
*Thi,
i, valid for rice fields,
pest i ci des.
**Compare also NYFFELER (1982).
which were not
or little treated with
-147KIRCHNER,1964). Some
field studies
had shown
that certain spider
species
'in the vegetation were ineffectjve against lepidopteran pests (POINTING,
1966; KIRCHNER, 1967; FURUTA,1977). According to data by the last
mentioned authors, some spider species could reduce butterfly populations
by 5% at the most. A slightly higher mortaljty was recorded by ENGEL
(1942), who estimated that during a pjne moth calamity, 12-23% of the
moth population was destroyed by spiders; but at the same time he also
observed that significantly less moths were killed by spiders than by
bugs. The ineffectiveness of certain spider species as predators of
butterflies might be connected with the
butterflies' ability,l981b).
to escape
.l967;
from these spjders'webs (KIRCHNER,
NYFFELER
& BENZ,
this negative effect may not be very important, since other
insects seem not to be killed at a higher rate by forest spiders. Thus,
for a comparison, the mortality of chestnut gall wasp populations as a
result of pnedation by spiders was of the same magnitude in norma'l
However,
years (7-20%) as that recorded by ENGEL for the pine moth (NAKAMURA &
1977). Contrary to what has been said so far, some other
authons have assumed that spiders can be important predators of
Lepidoptera, aphids, and mosquitos in the vegetation zone of forest
,l968a,
NAKAMURA,
(SUBKLEt/J, 1939t JUILLET, 1961i,
ecosystems .l968t
b; LUCZAK,
FOX & GRIFFITH, 1976).
DABROWSKA-PROT
et al.,
Like the forests, orchards are also tree ecosystems. Field studies
shown that spiders form a frequent pnedator group in pesticide-free
have
orchards (HARRISON, 1968; MacLELLAN, 'l973; CARROL, 1980). Several authors
have therefore supposed that spiders play an important role as insect
predators in pesticide-free orchards (CHANT, 1956; KAYASHIMA, 1972;
'l973; MANS0UR
'l980a), though precise results do not
MacLELLAN,
_e! al.,
exist. However, it has been demonstrated that the treatment of
orchards with pesticjdes leads to a sjgnificant
reduction of the density
.l979;
of spiders (CHANT, i956; SPECHT & DoNDALE, .l960;
D0NDALE et al.,
-l980).
'inä-icates
MANS0UR S! ql., 1980b; f4cCAFFRtY & HORSBURGH,
Th'is
that
pesticide treatments reduce the effectiveness of spiders as insect
jn
predators
orchards.
4.11. Using spiders in "biological pest control"
Ground-dwelling spiders, together with the ground-dwelling raptorial
Carabidae and Staphy'linidae, form an important predator
potential in
cereal fields. This predator potential can be uti'lized within
"programs
for integrated pest control" (BASEDoW & MIELKE, 'l977; KIRITANI,1979).
Thus, attempts have been made jn Japan to raise the spider density in
rice fields artif.icial'ly by releasing Drosophila fl ies. This additional
food then caused an increased fertility in the spiders (KOBAYASHI,,l975).
According to a report of the Chinese News Agency Xinhua of August 'l5,
1979, in the Peoples Republic of China spiders are introduced into rice
fjelds as biological control agents of rice pests.
it would probably be difficult to breed
of spiders in the laboratory. RUPPERTSHOFEN ('l976) and
KAYASHIMA (1967) have looked for an alternative. They have proposed that
egg sacs of spiders could be gathered somewhere and placed jn forests or
mulberry plantations respectively to raise the population density of
As most spiders are cannibals,
large
numbers
spi ders
.
_ 148 Another example on the use of spiders for biological pest control is
reported from South Africa. There, spiders were settled in houses.
STEYN (1959) recorded a reduction of the f1y populations by 99% within
2ll2 months and, at the same timö, a pronounced decrease of gastro-
jntestinal infections of
men
in that region,
because
the vectors of
disease were destroyed.
llhat about the possibility of utilizing spiders for biological pest
control in Switzerland? Here, spiders could only become of greater
importance, if it were possible to increase the spider density in cultivated fields. This would be possible if the area of the "ecological cells"
(abandoned grasslands, hedges, wet areas,
etc.),
which serve as predator-
reservoirs for agroecosystems, could be enlarged. However, uncultivated
lands of that kind may serve as reservoirs for predators and pest
organisms as well. The expansion of the area of the "ecological cells"
could therefore also bring about an increase of pest incidence. l,Jith
it is difficult to estimate,whetherthe useful
effect (reservoirs of predators) or the detrimental effect (neservoirs
of pests) would ultimately prevail, Intensive research on the complex
functions of such "ecological cells" in the agricultural landscape would
be necessary, before the expansion of their area with the intentions of
present day knowledge
increasing the predator density
recommended.
in the cultivated
aneas could
be
I49
5.
ZUSAMMENFASSUNG
'l976-'l979
wurde die 0ekoiogie von Spinnen in unbewirtschafteten
Graslandbiotopen, Mähwiesen und Getreidefeldern bei Zürich (Schweiz)
untersucht. In solchen Oekosystemen leben Spinnen in zwei Straten,
Von
1) auf der Bodenoberfläche,2) jn der Vegetationsschjcht. Wir finden jn
den beiden Straten verschiedene Spinnengemeinschaften.
In unbewirtschaftetem Grasland leben die Spinnen während des ganzen
Jahres ungestört. Sie können daher in solchen Biotopen in der Vegetationsschicht relativ grosse Populationen aufbauen (bei Zürich: ca. 10
Spinnen/ml, in Literatur wesentlich höhere Werte). Demgegenüber werden
Kulturfelder peniodisch gemäht, wobei die Lebensräume und Eikokons vieler
Spinnen zerstört werden. In der Vegetationsschicht von Kullurfeldern
leben daher nur kleine Spinnenpopuiationen (ca. I Spinne/mz in Mähwiesen,
0. l-0.6 Spinnen/ma in Getreidefeldern). Die Bodenobe4fläche von Kulturfeldern ist reiqtiv dicht besiedelt (15-42 Spinnen/mz in Mähwjesen,
l0-50 Spinnen/mz in cetreidefeldern).
Die Spinnen in der Vegetationsschicht von !l'iesen und Getreidefeldern sind
prjmär Prädatoren von Diptenen und Honopteren. In der Vegetatjonsschicht
unbewirtschafteter l^liesen können zusätzlich Bienen und/oder Heuschrecken
einen essentiellen Antejl an der Beutebiomasse grosser Netzspinnen ausmachen. Auf der Bodenoberfläche von Mähwiesen und Getreidefeldern sind
die
dominanten Spinnen hauptsächlich Prädatoren von kleinen, weichhäutjgen Insekten (Co11embolen, Blattläuse, Dipteren etc. ). Aus den Nahrungsanalysen geht hervor, dass die Spinnen Prädatoren sowohi von Schadinsek-
ten (2.8. Getreideblattläuse) als auch von Nutzarthnopoden (Honigbienen,
Chrysopiden, Coccinelliden etc.
) sind.
Der Energiefluss (= prey killed) durch die Spinnengemeinschaften der
Vegetationsschicht von Brachlandbiotopen kann hoch sein (2.B. in einem
Hochstaudenried: >900 MJ/halJahr). Demgegenüber ist der Energiefluss
durch die Spinnengemeinschaften von Kulturfeldern s i gnif i kant niedri ger
(in Getreidefeldern: l.l-6.5 MJ/ha/Jahr, in Maisfeldern: (0.5 MJ/ha/Jahr).
Der Energiefluss durch die bodenbewohnenden Spinnengemeinschaften der
Kulturfelder dürfte in der Grössenordnung von l0-50 MJ/ha/Jahr Iiegen.
Unbewi
ntschaftete
Grasl and-oekosysterne ste l l en
oft
wahre "Spi nnenpara-
diese" dar. In solchen Oekosystemen stellen die Spinnen der Vegetationsschicht eine wichtige Prädatorengruppe dar. Im Gegensatz dazu scheinen
Spinnen in der Vegetationsschicht von Getreidefeldern keine ökologische
Rolle zu spielen. Inwieweit in den Mähwiesen und Getrejdefeldern die
epigäischen Spinnen eine ökologische Bedeutung haben, werden erst künftige Studien zeigen.
150 -
6.
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_174_
Curriculum vitae
Educational BaglEound:
March 25th,
I 970- I 976
I 950
Eorn in Zurich, as son of Hans Nyffeler, teacher, and
of Irma Nyffeler-Brunnhofer
at the Faculty of Agronoqy of the ETH Zurich.
Specialisation in Crop Science and Entomology.
During this time practical experience at the Natural
History l,luseum Basel in winter l97l (supervision:
Prof. Dr. Stefan 6raeser), the Swiss Federal Research
Station for Agronoqy Zurich-Reckenholz in surrmer 1972
(supervision: Dr. Ferdinand l,leilenmann), and the
Studies
Entofiological Laboratory of the Sxiss Federal Research
Stötlon lladenswil in summer 1973 (supervision: Drs.
Th. l,lildbolz and E. llani).
Graduation with the Diplrima degree of 'Engirteer in
Agronoqy"
r
976- 1 982
Scientific assistant at the Departnent of
I
Entomology
prepared the present thesis under the supervision of Prof. Dr. Georg Benz. Teaching assistant in
Biology-courses for undergraduate students.
where
Explor.ations
1972-1973
in Natural
Sciences:
In the Tessin AIpes I discovered an Ag-Pb-8i-Sulfosalt,
which was identified by Prof. Dr. Stefan Graeser,
University of 8asel, to be probably a new mineral
(publication in prep.)
pr_i zes :
prize at the znd Swiss Science Fair (Schweizer
forscht) for a field study in Natural Sciences
(Contest-President: Prof. Dr. Adolf Portmann)
968
Second
Jugend
I 971
Second
ilugend
I
prize at the sth Swiss Science Fair (Schweizer
forscht) for a field study in Natural Sciences
(Contest-President: Prof. Dr, Adolf Portmann)