Download Araneae: Salticidae

zoological Journal of the Linnean SocieQ (1994), 110: 77-102. With 15 figures
The comparative study of the predatory
behaviour of Myrmarachne, ant-like jumping
spiders (Araneae: Salticidae)
R O B E R T R. JACKSON
Department of <oology, University of Canterbury, Christchurch, N e w zealand
AND
MARIANNE B. WILLEY
Department of Entomology, Clemson University, Clemson, South Carolina 29634, U.S.A.
Received September 1992, revised and accepted f o r publication M a y 1993
T h e predatory behaviour of 31 species of Myrmarachne, ant-like salticids, was studied in the
laboratory and the field. T h e ant-like morphology and locomotion of these spiders appears to
function primarily in Batesian mimicry. No evidence was found of Myrmarachne feeding on ants.
However, predatory sequences were found to differ considerably from those typical of salticids.
Instead of stalking and leaping on prey, Myrmarachne lunged at prey from close range. Myrmarachne
used its legs I to tap prey before lunging, another unusual behaviour for a salticid. Myrmarachne fed
on a wide range of arthropod prey in nature and the laboratory, but appears to be especially
efficient at catching moths. Also, Myrmarachne tends to open up, or enter into, other spiders’ nests
and eat other spiders’ eggs. Myrmarachne males were less efficient than females, in laboratory tests, a t
catching various types of arthropod prey, but they appear to be as efficient as females a t oophagy.
Myrmarachne tend to use webs of other spiders as nest sites, but no evidence was found of Myrmarachne
preying on spiders in webs. It appears that the unusual features of Myrmarachne’s predatory and
nesting behaviour are important in enabling these spiders to preserve their ant-like appearance.
ADDITIONAL KEY WORDS: -Spiders
-
mimicry
-
predation - salticids.
CONTENTS
Introduction .
. . . . . . . . . . . . . .
Materials and methods
. . . . . . . . . . . .
Observations . . . . . . . . . . . . . . .
Nest structure and nest sites in nature.
. . . . . . .
Clamps.
. . . . . . . . . . . . . .
Observations of predation in nature .
. . . . . . .
Myrmarachne in salticid nests in n a t u r e ,
. . . . . . .
Locomotion .
. . . . . . . . . . . . .
Cursorial predation on vestigial winged fruitflies .
. . . .
Cursorial predation on normal winged flies and on spiders . . .
Cursorial predation on moths . . . . . . . . . .
Cursorial predation by females versus cursorial predation by males .
. . . . . . . . . . .
Interactions with ants
Responses of Myrmarachne adults to nests and eggs of other spiders .
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0 1994 T h e Linnean Society of London
78
R.. R. JACKSON AND M. B. WILLEY
Discussion
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Mimicry . . . . . . . . . .
Cursorial predation . . . . . . .
Oophagy . . . . . . . . . .
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Use of alien webs as nest sites.
Male versus female predaiory behaviour . .
Relationship between ant mimicry and predatory
Generalizations about the genus Myrmuruchne .
Acknowledgements
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References
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I N 1 RODUCTION
Myrmarachne is a genus of predominantly tropical jumping spiders (Salticidae)
which resemble ants in body form and locomotory behaviour (Wanless, 1978).
More than 160 species of IlQrmarachne have been described, and these spiders are
probably Batesian mimics of the ants with which they are often associated
(Mathew, 1954; Edmunds, 1974, 1978). The present paper is a comparative
study, in the laboratory and the field, of the predatory behaviour of 31 species of
Myrmarachne. Previous work (Jackson, 1986a) included data for one species,
M.lupata, in the laboratory, and 1 1 prey records from eight species in the field.
Three questions are considered in the present paper.
( 1 ) What kinds of prey are eaten by Myrmarachne and how does the prey of
Myrmarachne compare with that of other salticids? In particular, do any species of
Myrmarachne regularly prey on ants? All species of Myrmarachne probably live in
association with ants (Wartless, 1978) and appear to have frequent opportunity
to eat their presumed models, but no species of Myrmarachne are known to prey
routinely on ants (Mathew, 1954; Edmunds, 1978). Predation on ants is of
interest because, except for a few specialized ant-predators (Edwards et al., 1974;
Cutler, 1980; Jackson & van Olphen, 1991, 1992), none of which are ant-like in
morphology or locomotory behaviour, salticids appear rarely to prey on ants.
(2) What methods are used by Myrmarachne to catch prey and how do these
compare with the prey-capture methods of other salticids? Salticids have
complex eyes and acute vision (Blest, 1985). Most species slowly stalk insects,
then leap on them when close (Forster, 1982). M.lupata (Jackson, 1986a), in
contrast, runs up to its prey, uses its legs to tap it rapidly, then attacks by lunging
(legs stay on substrate) instead of leaping (legs leave substrate). How common
this unusual prey-catching behaviour is in the genus Myrmarachne is unknown.
Also, M. lupata eats other spiders’ eggs (Jackson, 1986a), which is unusual for
salticids (Jackson, unpubl. data), but how common feeding on eggs is in the
genus Myrmarachne is unknown.
(3) How does the predatory behaviour of Myrmarachne males compare to that
of Myrmarachne females? The males of many species of Myrmarachne have very
large chelicerae (Wanless, 1978), the length of the male’s chelicerae often being
3 3 O / , or more of the length of his body from the eyes to the tip of the abdomen,
but how cheliceral size might influence the course of predatory sequences is not
well understood.
I n addition to data on predatory behaviour, we present other data that are
relevant to understanding fclyrmarachne’s predatory behaviour: data on nest sites
used by Myrmarachne in nature and data on Myrmarachne’s normal style of
locomotion.
COMPARATIVE STUDY OF MYRMARACHNE
79
MATERIALS AND METHODS
Thirty one species of Myrmarachne were each studied in the field and in the
laboratory in Christchurch, New Zealand (Table 1). Also, previously
unpublished field data on M.lupata and on unidentified Myrmarachne juveniles
are presented. For laboratory studies of Myrmarachne, a variety of insects and
spiders were used as prey (Table 2).
TABLE
1 . Myrrnarachne studied in the laboratory
Species
Collection
locality
Number
M . elongata Szombathy
M . gelongi
M . giltayi Roewer
M . kiboschensis Lessert
M . kilifi Wanless
Kenya
Singapore
Kenya
Kenya
Kenya
2
3
3
27
M . Eaurentina Bacelar
Kenya
15
M . lawrencei Roewer
M . luctuosa (L. Koch)
Kenya
Australia
24
15
M . marshalli Peckham & Peckham
maxillosus (C. L. Koch)
melanocephala MacLeay
militaris Szombathy
naro Wanless
M . plataleodes (0.P.-Cambridge)
M . providens Peckham
M . panamensis Galiano
Kenya
Singapore
Singapore
Kenya
Kenya
Sri Lanka
Sri Lanka
Costa Rica
28
20
16
21
22
55
4
M . parallela Fabricius
Costa Rica
17
M . striatipes L. Koch
Australia
19
M . uvira Wanless
M . cf exasperans
Kenya
Sri Lanka
15
M . cf kitale Wanless
Kenya
12
M . cf richardsi Wanless
Kenya
27
M . A sp. A
Australia
16
M . A sp. B
M . A sp. C
M . A sp. D
M . I sp. c
M. SL sp. A
Australia
Australia
Australia
India
Sri Lanka
6
6
5
1
8
M . SL sp. B
S r i Lanka
8
M . SL sp. D
M . SL sp. E
Sri Lanka
Sri Lanka
12
M.
M.
M.
M.
4
10
13
4
Use
Standard tests
Standard tests
Standard tests
Standard tests
Standard tests, salticids, moths, attended
eggs, unattended nests (no eggs)
Standard tests, salticids, small moths, large
moths, attended eggs, unattended nests (no
eggs)
All
Standard tests, houseflies, gnaphosids,
salticids, small moths, large moths
All
All
All
All
All
All
Standard tests, large moths
Standard tests, salticids, small moths, large
moths
Standard tests, houseflies, gnaphosids,
salticids, small moths
Standard tests, houseflies, small moths, large
moths
All
Standard tests, gnaphosids, attended eggs,
unattended nests (no eggs)
Standard tests, large moths, attended eggs,
unattended nests (no eggs)
Standard tests, gnaphosids, salticids, large
moths, attended eggs, unattended nests (no
eggs)
Standard tests, gnaphosids, salticids, large
moths, attended eggs, unattended nests (no
eggs)
Standard tests
Standard tests
Standard tests, houseflies, small moths
Standard tests
Standard tests, houseflies, small moths, large
moths
Standard tests, gnaphosids, salticids, large
moths, attended eggs
Standard tests, small moths
Standard tests, houseflies, gnaphosids, large
moths, attended eggs
Standard tests: vestigial and normal winged fruitflies, ants, unattended eggs.
TABLE
2. Spiders and insects used in laboratory studies of Myrmarachne
Species
Order
Family
Source
..lnraciia gemmea (Dalmas)
Araneae
Gnaphosidae
New Zealand
Bar$ia aericeps Simon
Araneae
Salticidae
New Zealand
Chelanrr antnrctica
Clubiona camhridpei (I,,
Koctir
Hymenoptera
Araneae
Formicidae
Clubionidac
New Zealand
New Zealand
Colopsus cancellatus Simon
Araneae
Salticidar
Sri Lanka
Cosmophasis olarina (Simon)
Araneae
Salticidae
Sri Lanka
Cnsmophasis micarioides (L.
Kochl
Araneac
Saltiridae
Australia
New Zealand
Sri Lanka
Use
Cursorial predation. Eggs
in unattended and
attended nest
Eggs in unattended and
attended nest
Cursorial predation
Cursorial prcdation. Eggs
in unattended and
attended nest
Eggs in unattended and
attendrd nest
Eggs in attended and
unattended nrst
Cursorial predation. Eggs in
unattended and attended
nest. Unattended nest
without eggs
Cursorial predation
M’eb source
Ctenopseutu sp.
(iyrfophora cicatroJa (E’orskal)
Drnmphila mrlunupaster
!,Meigen i
Epeu sp.
Lepidoptera
Araneae
Tortricidae
Araneidac
Diptera
Aranear
Drosophilidae Culture
Saltiridae
Singapore
Hasarius adonsoni (Audouin)
Araneae
Saltiridae
Australia
Aranexe
Hymenoptera
Araneae
Araneidae
Formicidae
Pisauridae
Sri Lanka
New Zealand
Australia
Web source
Cursorial predation
Web source
Araneae
Lepidoptera
Araneae
Dipluridae
Noctuidae
Salticidae
Kenya
New Zealand
Kenya
Web source
Cursorial predator
Cursorial predation. Eggs
in unattended and
attended nest
Cursorial predator
Herunnia ornatisszma
(Doleschall)
Huberia striata
Znola rubtilis Davirs
‘Thelochoris karschi Bosenberg
& Lenz
Melancha sp.
Menemerus sp.
M u c a domejlica (Linnaeus)
Plexippus culiciuorous
Doleschall
Diptera
Muacidae
Culture
Araneae
Saltiridae
Singapore
Prolasius aduena
Pjeudicius sp. I
Hymenoptera
Araneae
Formicidae
Salticidae
New Zealand
Kenva
Sandalodes semicupreus
Siler semiglaucus Simon
Stegodyphus sarasinorum
Karsch
Tauala lepidus Wanless
Araneae
Araneae
Araneae
Salticidae
Salticide
Eresidae
Sri Lanka
Sri Lanka
Sri Lanka
Araneae
Salticidae
Australia
7~a?ellinluenseyeru (Thorell)
Araneae
Saiticidae
Singapore
Trite planiceps Simon
Araneae
Salticidae
New Zealand
Unknown ant
Viciria praemandibularis
(Hasselt)
Hymenoptera Formicidae
Costa Rica
Araneae
Singapore
Salticidae
Cursorial predation
Eggs in unattended and
attended nest. Unattended
nest without eggs
Cursorial predation. Eggs in
unattended and attended
nest. Unattended nest
without eggs
Cursorial predation. Eggs in
unattended and attended
nest. Unattended nest
without eggs
Cursorial predation
Cursorial predation. Eggs
in unattcndcd and
attended nest
Eggs in unattended nest
Eggs in unattended nest
Web source
Cursorial predation. Eggs
in unattended and
attended nest
Cursorial predation. Eggs
in attended and
unattended nest
Cursorial predation. Eggs in
attended and unattended
nest. Unattended nest
without eggs
Cursorial predation
Eggs in unattended and
attended nest
COMPARATIVE STUDY OF MYRMARACHNE
81
Maintenance, general testing procedures and terminology were identical to
those used in previous studies (see Jackson & Hallas, 1986). This included the
convention that the expressions ‘usually’, ‘sometimes’ and ‘rarely’ were used to
indicate frequencies of occurrence of > SOY0, 20-80y0 and < 20%, respectively.
Observations of Myrmarachne occupying webs of other spiders in nature (Table
3) were followed up in the laboratory by using web-building spiders set up in
glass tanks, containing sticks for web attachment. Except for Stegodyihus
sarasinorum, a social spider (see Bradoo, 1972), web spiders were set up one per
tank; 5’. sarasinorum was set up with 50 spiders per tank which were allowed to
build communal webs. Some spiders had egg sacs in their webs in the laboratory,
and there was detritus (dead leaves, prey remains and spider exoskeletons)
suspended in the silk of all webs. I n these tests, one Myrmarachne was introduced
into each tank after the web-building spiders had spun webs. Ants, flies and
moths were released into the tanks periodically, and observations were made
intermittently over a period of at least one month.
Other tests were carried out in standard maintenance cages (see Jackson,
1974) in the absence of webs. An insect or a hunting spider was put into a cage
with a Myrmarachne, or a Myrmarachne was put into a cage containing either a
hunting spider in a nest with her eggs or a nest with eggs but no hunting spider
present.
Data were analysed using tests of independence. Because no significant
interspecific differences in behaviour were evident, the term ‘Myrmarachne’ is used
in the text for all observations that apply to all of the species in Table 1.
However, species are named whenever all species were not observed. Prey was
identified to the lowest taxon feasible.
OBSERVATlONS
Nest structure and nest sites in nature
For a nest, Myrmarachne spun a flattened tube with a ‘door’ (i.e. a natural
opening) at each end. Nests in nature and nests occupied for more than a few
days in the laboratory tended to be dense and opaque, and the silk often had a
fluffy, or woolly, texture (Fig. 1).
Nests were usually found on either the tops or undersides of large waxy green
leaves (in diameter, more than twice the length of the nest). However,
M . plataleodes sometimes built nests on dead brown leaves still attached naturally
to trees and shrubs, inside dead rolled-up leaves still attached naturally (i.e. no
‘clamps’; see below) to trees and shrubs, in crevices on boulders, or under bark of
trees. Also, M . luljata was sometimes found inside dead rolled-up leaves ‘clamped’
by silk to the substrate (see below).
There were 85 records from the field of Myrmarachne in nests on detritus (dead
brown leaves, seed pods or pieces of bark) suspended in webs of other spiders
(Table 3). Spiders with which Myrmarachne cohabited belonged to eleven families
(Fig. 2). There was about an even split between occupancy of sticky and nonsticky webs (49% sticky and 51% non-sticky). ‘Sticky’ webs are webs coated
with either cribellar wool or ecribellate droplets of fluid ‘glue’ from the spider’s
aggregate glands. Of the 40 sticky webs, 73% were cribellate and 27% were
ecribellate. Shapes varied (Fig. 3), but sheet webs were the most common.
Agelena leucopyga
Smeringopus pallidus (Blackwell)
ThelochorG karshi
Cyrtophora cicatrosa
Mature Male Cohabiting with
Subadult Female
M . kzl$
M . plataleodes
Stegodyphus sarasinorum Karsch
Thelochoris karshi Bosenberg & Lenz
Agelena leucopyga Pavesi
Achaearanea krausi Chrysanthus
Inola subtilis Davies
Nephilengys malabarensis (Walckenaer)
Phonognatha sp.
Psilochorus sphaeroides (L. Koch)
Agelena leucopyga
Cyrtophora cicatrosa (Stoliczka)
Dendrolycosa sp.
Psechrus torvus (0.P.-Cambridge)
Dendrolycosa sp.
Thelochoris karshi
Cyrtophora sp.
Achaearanea decorala (L. Koch)
M. naro
M. plataleodes
M . provzdens
M . cf richardsi
Myrmarachne Asp.A
Myrmarachne A@.
Solitary Mature Myrmarachne Male
M . naro
M . plataleodes
M. lupata
'44.exasperam
M . kiliJi
M . laruenlia
Solitary Mature Myrmarachne female
Species of web spider
Dipluridae
Araneidae
Agelenidae
Pholcidae
Eresidae
Dipluridae
Agelenidae
Theridiidae
Pisauridae
Araneidae
Araneidae
Pholcidae
Agelenidae
Araneidae
Pisauridae
Psechridae
Pisauridae
Dipluridae
Araneidae
Theridiidae
Family
Kenya
Sri Lanka
Kenya
Sri Lanka
Sri Lanka
Kenya
Kenya
Australia
Australia
Australia
Australia
Australia
Kenya
Sri Lanka
Sri Lanka
Sri Lanka
Sri Lanka
Kenya
Australia
Australia
Locality
1
I
1
15
1
2'
I
1
2
I*
1
1
1
2'
2'
1
1
2
3'
1
No.
observations
__
Web type
Sheet. Non-sticky
Dome. Complex. Non-sticky
Communal sheet. Non-sticky
Dome. Non-sticky
Communal sheet. Cribellate
Sheet. Non-sticky
Communal sheet. Non-sticky
Space. Ecribellate sticky
Sheet. Complex. Non-sticky
Orb. Ecribellate sticky
Orb. Ecribellate sticky
Dome. Non-sticky
Communal sheet. Non-sticky
Dome. Complex. Non-sticky
Sheet. Non-sticky
Orb. Ecribellate sticky
Sheet. Non-sticky
Sheet. Non-sticky
Dome. Complex. Non-sticky
Space. Ecribellate sticky
TABLE
3. Observations of Myrmarachne occupying spider webs i n nature. H o s t spider present i n each instance
N
CD
Dipluridae
Psechridae
Kenya
Sri Lanka
Sri Lanka
Kenya
Pholcidae
Eresidae
Smringopus pallidus
Stegodyphus mimosarum ( Pavesi)
Thelachoris karshi
Fecenia macilenta
Australia
Kenya
Australia
Australia
Sri Lanka
Sri Lanka
Sri Lanka
Sri Lanka
Australia
Kenya
Australia
Sri Lanka
Australia
Australia
Australia
Theridiidae
Agelenidae
Amaurobiidae
Amaurobiidae
Araneidae
Pisauridae
Psechridae
Araneidae
Pisauridae
Dipluridae
Pholcidae
Araneidae
Oecobiidae
Uloboridae
Araneidae
Achaearanea krausi
Agelena leucopyga
Badumna candida (L. Koch)
Badumna insignis (L. Koch)
Cyrtophora cicatrosa
Dendrolycosa sp.
Fecenia macilenta (Simon)
Herennia ornatissima (Doleschall)
Inola subtilis
Thelochoris karshi
Micromerys gracilis Bradley
Nephilengys malabarensis
Oecobius annulipes
Philoponella uariabilis (Keyserling)
Phonognatha sp.
*Myrmarachne juveniles can not be identified accurately to species
'One of thcsc was in nest brooding eggs.
'Brooding eggs in nest.
'One of these was in nest with shed exoskeleton.
'Two of these in nests with shed exoskeletons.
'In nest with shed exoskeleton.
Group of Recently Hatched
Myrmarachne Juveniles*
Solitary Myrmarachne J uveniles*
1
2
1
2
1
11
1
1
1
3
2
63
1
1
53
14'
3
Sheet. Non-sticky
Orb. Cribellate
Space. Ecribellate sticky
Communal sheet. Non-sticky
Communal sheet. Cribellate
Sheet. Complex. Cribellate
Dome. Complex. Non-sticky
Sheet. Non-sticky
Orb. Cribellate
Orb. Ecribellate sticky
Sheet. Complex. Non-sticky
Sheet. Non-sticky
Space. Under leaf. Non-sticky
Orb. Ecribellate. Sticky
Sheet. Cribellate
Orb. Complex. Cribellate
Orb. Leaf at hub. Ecribellate
sticky
Dome. Non-sticky
Communal sheet. Cribellate
co
W
5
Yc
COMPARATIVE STUDY O F MYRMARACHNE
El
80
70
0
1
60
c
.
‘
S
50
’
$
40
El
1
30
85
Communal Sheet
Sheet Complex
Solitary Sheet
Orb Complex
Solitary Orb
Dome Complex
Solitary Dome
Space Solitary
20
10
0
Sheet
Orb
Dome
Type of Web
Space
Figure 3. Observations of Myrmarachne occupying spider webs in nature (see Table 3). Host spider
present in each instance. Data summarized according to percentage of total number of observations
of Myrmarachne for which the host spider’s web was of different types.
About half (51 yo) of the webs occupied by Myrmarachne belonged to ‘social
spiders’ (i.e. either ‘communal and non-territorial’ species that live in shared
communal webs or ‘communal and territorial’ species that live in complexes of
interconnected, but individually occupied, webs; for terminology, see Jackson,
1978). These social spider webs included complexes of sheet, orb and dome webs,
as well as communal sheet webs (Fig. 3).
Myrmarachne sometimes moults, mates and oviposits in webs; some of the
Myrmarachne in nests in webs were females with eggs and some were cohabiting
pairs (adult male with subadult female). Also, some of the Myrmarachne in webs
had shed exoskeletons in their nests (Table 3).
Achaearanea krausi is a theridiid spider in Queensland, Australia, that spins a
space web and places a dead rolled-up leaf in its web for a nest. Females of
A . krausi place their egg sacs in these leaves. In addition to the observations in
Table 3 , there were nine instances in which a M . lupata was found in the field
(Australia) inside a rolled-up leaf in an A. krausi (Theridiidae) web, but with the
host theridiid absent. However, in each instance, egg sacs of the theridiid were
present in the leaves. Six of these rolled-up leaves contained an adult M . lupata
female with her own eggs in a nest; one had a juvenile with a shed exoskeleton in
a nest, and one had a cohabiting pair (adult male plus subadult female) inside a
nest.
O n five occasions, remains of dead Myrmarachne were seen in A . krausi webs in
the field (Australia). I n each instance, A. krausi was present and the Myrmarachne
was wrapped up in silk. Four of these Myrmarachne had evidently been eaten
already by the theridiid (the Myrmarachne was only a dried up shell), and the
theridiid was in the act of eating the fifth. These five Myrmarachne,being in poor
condition, could not be identified with certainty, but they appeared to be
M.lupata.
86
R. R J A C K S O N A N D M. B. WlLLEY
Clamps
‘lwenty two M . lupata females were found nesting in dead, brown, partially
rolled-up leaves that were attached to the substrate by a dense mass of silk lines
from the petiole of the leaf to the substrate that kept the leaf tightly attached. We
called these silk attachments ‘clamps’, and they usually held the leaf no more
than c. 2 mm from the substrate. T h e substrate was a twig ( 1 5) on a tree or
shrub, a tree trunk (4), a boulder (2) or a rock ledge ( 1 ) . These clamps were
similar to those previously described for Simaetha paetula a n d Simaelha lhoracica
from Australia (Jackson, 1985).
I n the laboratory, 29 M . lupata females were kept in glass tanks with a network
of dead twigs above an d dead, rolled-up leaves distributed across the floor. T w o
of these M . lupata eventually clamped a leaf to a twig and build a nest on it.
Unfortunately, we were never present when the leaf was lifted u p into place on
the twig.
ObJeruationJ on predation in nature
There were 30 instances in which Myrmarachne was observed feeding in nature
(Table 4): 20 mature females belonging to 14 species, four mature males
TABLIT.
4. Obw-vations of Myrrnamh1e frrding in naturc
COMPARATIVE STUDY OF MYRMARACHJVE
40
87
1
W
Prey Items
ticlonging t o four species, and six juveniles. There was no evidence that prey size
Lraried with the species o r sex-size c h s r of the M-yrmnrachne. Pooling data, 48"{, of
the prey were medium in size, 35"; were small and 16", were large (see
'l'able 4 for definition of size). More than half (6l0dI)of the prey were Diptera
and Lepidoptera (Fig. 4 ) .
Myrmarachne in salticid nests in nature
l'here were 37 instances ('l'able 5) in which a Myrrnarachrie was found in nature
in a n 'alien' salticid nest (i.e. a nest i t did not itself build). In eight (22"!,,) of
these instances, a small M-yrmarachnr juvenile was found i n a nest occupied by a
mature salticid female with eggs (Fig. 4). In thrce of these eight instances, the
othcr salticid was another iVyrmnrachne, but whether the adult and juvenile werc
corispecific could not he determined. In another 18 (49'j,, of 37) instaiices? a
.I.lyrmarnchrre was fbund in salticid nests containing eggs but n o spiders; eight of
these were iV(yrmiirar1zne nests (species unknown), arid the other 10 were i n nests
of salticids from othcr gcncra (proliablc genus, or genus and species, was cvident
I'or only five of these). Another 1 1 (30",, of 37) M-yrrnarachrte were in iicsts alone
(no othcr spidcr and iic) eggs present). Four of these werc nests of :V!vrmamchni>
(species unknown), one was a nest of a Jacksonoides quee~i.slnndirriand thc other six
kvere nests of indetermiriate gcricra.
Chisidering all 37 instances of' M_)~rmii~-ihnr
found in alicn nests, 4 1
were
ju\,eniles occupying alien Myrmarurhnr nests. It is unlikely that these M-ilrmarachnP
0
Ll
Q)
30
20
10
0
With adult salticid and eggs
With eggs only
Alone
COMPARATIVE STUDY OF MYRMARACHNE
89
Locomotion
Myrmarachne's walking gait resembled that of an ant: the spider stepped
rapidly, frequently changed speed and direction of movement, and tended to
move continuously for several minutes at a time before pausing. Both while
stepping and while pausing, Myrmarachne moved its abdomen smoothly and
rhythmically up and down (0.5-1.0mm, 1-2/s), with a slight side-to side
wobble.
Myrrnarachne moved its slender legs I in a manner resembling an ant's waving
antennae. These legs were extended loosely in front of the body (i.e. there was
slight flexion maintained at the femur-patella joints), and movement (primarily
femoral) was of variable, but generally large (2-5 mm), amplitude. Tarsi often
touched the substrate during the downward part of each waving cycle.
Although all species of Myrmarachne studied occasionally leapt to cross gaps of
2-3 body lengths, leaping was not a regular mode of locomotion for these spiders.
For example, when confronted by a space between two leaves, Myrmarachne
usually paused briefly, then moved off in another direction. Also, if a
Myrmarachne was being harassed (e.g. by an arachnologist attempting to collect
it), then, instead of leaping away, it usually either stepped faster and scurried
around sides of leaves or it dropped from a leaf and allowed itself to fall, usually
on a dragline, to either another leaf or the substrate below.
Cursorial predation on vestigial winged fruitjies
Myrmarachne usually did not appear to respond until it was facing a fly about
one body length away. Then it suddenly brought its waving legs I, with tarsi
1-2 mm apart, forward over the fly. If the fly remained stationary, Myrmarachne
lunged and seized the fly, with or without tapping it first.
Because these sequences were very rapid, details were difficult to discern. I t
appeared, however, that attacking without first tapping was more common if the
fly was initially facing directly toward the Myrmarachne. This was confirmed from
analyses of video tapes of 52 predatory sequences (Fig. 6). Myrmarachne tapped
more often when orientation was 0" than when orientation was 90" or 180"
(P< 0.001).
While tapping, legs I moved up and down (c. 5/s), with femur-patella and
tibia-metatarsus joints being held flexed at c. 45" and 15", respectively, and with
tarsi repeatedly contacting the fly on the down stroke. Tapping usually lasted for
only c. 0.5 s before Myrmarachne attacked or before the fly moved away, although
Myrmarachne sometimes stood and tapped for as long as 10 s.
A fly being tapped usually remained stationary, although it might pivot, step
slightly backwards or step slightly to the side. However, if a fly walked away,
Myrmarachne usually followed, continuing to tap, then lunged forward and seized
the fly behind the head.
Prior to attacking without tapping, Myrmarachne sometimes stood with legs in
place for as long as 5 s before lunging, during which time the fly stayed
quiescent. The lunge usually came when the fly began to walk away.
Myrmarachne lunged by extending legs I11 and IV, keeping tarsi on the
substrate and forcing the body rapidly forward. Legs I returned, after the lunge,
to their normal position at the side and were not used to pull in the fly.
R. R. JACKSON AND M. B. WILLEY
90
0
W
Attacked without tapping
Tapped before attacking
goo
180'
Orientation
Figure 6. Analysis of videotapes of 46 predatory sequences of M . lupata and M. plataleodes families
(equal sample sizes; data pooled). Myrmarachne with vestigial winged fruitflies. For each orientation
of prey to hQrmarachne, data summarized according to percentage of attacks that were or were not
preceded by A4vrmarachne tapping prey. N o . of observations at each orientation: 0"(?2), go"( 13),
180"1171.
Myrmarachne sometimes turned toward an active fly that was as far as 100 mm
away, then approached in spurts (rapidly stepping forward for c. 0.5 s, pausing
for c. 0.25 s, stepping for c. 0.5 s again, etc), sometimes waving legs I while
spurting forward. At the end of the last spurt, Myrmarachne brought legs I
forward, lunged, and seized the fly. Usually Myrmarachne circled around the fly
so that it could lunge eithler head on or from the rear, sometimes tapping the fly
while circling it. There was no pause between stepping and lunging, and usually
none between initial orientation and starting to approach by spurting.
After catching a fly, Mjn-marachne usually carried it to a secluded place to feed.
Myrmarachne waved its leg!; in the usual way as it walked and i t usually continued
to wave its legs slowly (1--2/s) while feeding.
Cursorial predation on normal winged Jies and on spider5
Myrmarachne pursued gnaphosids, salticids, normal winged fruit flies and
houseflies in sequences sirnilar to the predatory sequences with vestigial winged
fruitflies. Although Myrmarachne pursued normal winged fruitflies about as often
as i t pursued vestigial winged fruitflies, it pursued houseflies and spiders less often
(Tables 1, 2).
Myrmarachne was less efficient at catching normal winged fruitflies than
vestigial winged fruitflies (Figs 7, 8), still less efficient against houseflies (Fig. 9)
and gnaphosids (Fig. 10) and least efficient against salticids (Fig. 11; Table 1, 2).
When Myrmarachne failed to catch arthropods other than salticids, it usually
appeared to be because the potential prey moved away soon after being touched
COMPARATIVE STUDY OF
80
MYRMARACHNE
0
H
-
91
Female
Male
1
60 c-‘ 50 c
$ 40 70
20 10 -
30
0-
Tap
Pursuit Tendency Capture Efficiency
Figure 7. Results from testing Myrmarachne with vestigial winged fruitflies in the laboratory. (See also
Tables 6, 7). Tap: percentage of tests in which Myrmarachne tapped prey. Pursuit tendency:
percentage of tests in which Myrmarachne attempted to catch prey. Capture efficiency: percentage of
prey pursued that were captured, Females’ capture efficiency greater than males’ (P<O.OOl).
Male-female comparisons NS for tap and pursuit.
by Myrmarachne. Salticids, however, were rarely touched by Myrmarachne.
Apparently, this was primarily because, with their well-developed vision, the
sal ticids could see and avoid an approaching Myrmarachne.
Myrmarachne never approached a salticid that was facing the Myrmarachne and
closer than c. 50 mm away. When Myrmarachne and another salticid less than
80
70
60
+
50
I=
a,
40
a
30
0
N
Female
Male
n
20
10
0
Tap
Pursuit Tendency Capture Efficiency
Figure 8. Results from testing Myrmarachne with normal winged fruitflies in the laboratory. Tapping
rate (P<0.005) and pursuit tendency (P<0.05) greater for males than for females, but females’
capture efficiency greater (P<O.OOl j than males’.
R. R. JACKSON AND M. B. WILLEY
92
70
50h
60
+
?
2
1
40
-
30
-
20
-
10
-
0
W
Female
Male
n
0
Tijp
Pursuit Tendency Capture Efficiency
Figure 9. Results from testing Myrmarachne with houseflies in the laboratory. Male-female
comparisons all NS.
50 m m apart faced each other, Myrmarachne often displayed by erecting legs I up
and to the side 45°C. This display has been described in detail previously for
M. lupata (Jackson, 1986a) and is used by M . lupata, and other Myrmarachne
(Jackson, unpubl. data), in interactions with conspecifics. The salticid sometimes
stopped and faced the displaying Myrmarachne for a few seconds, then moved
away, and the salticid never displayed at the Myrmarachne.
60
El
W
50
Female
Male
40
CI
S
Q,
2
30
Q)
a
20
10
0
lap
Pursuit Tendency Capture Efficiency
Figure 10. Results from testing Myrmarachne with gnaphosids in the laboratory. Male-frmalc
< omparisons all NS.
COMPARATIVE STUDY OF MYRMARACHNE
30
-
20
-
10
-
+
r=
93
8
L
al
a
O A
1
L
Tap
Pursuit Tendency
0
Female
Male
apture Efficiency
Figure 1 1 . Results from testing Myrmarachne with salticids in the laboratory. Tapping rate
(P<0.005) and putsuit tendency (P<0.005) greater for females than for males. Male-female
comparisons NS for capture.
A common sequence was for Myrmarachne to begin approaching a salticid that
was facing away; when Myrmarachne got close, the salticid turned around and
faced Myrmarachne, and Myrmarachne displayed and backed away. The salticid
then walked away, and Myrmarachne began to approach again. After several
sequences like this, the Myrmarachne usually stopped responding to the salticid.
When predation did occur, the salticid was usually small and facing away
while Myrmarachne approached. Myrmarachne approached rapidly and began
tapping the salticid from the rear. The salticid remained still for several seconds
while being tapped, after which Myrmarachne attacked it.
Cursorial predation on moths
Myrmarachne readily pursued moths, both large and small, and was efficient a t
catching them (Figs 12, 13).
Myrmarachne’s responses to moths and flies were similar except that tapping
bouts before attacking moths were sometimes as long as 20s and Myrmarachne
almost always attacked moths head on. Moths sometimes moved their legs and
antennae while being tapped by Myrmarachne, but they rarely moved away.
Over all, pursuit tendency, capture efficiency and frequency of tapping in tests
with small moths were slightly less than they were in tests with vestigial winged
fruitflies, and the values for large moths were slightly less than those for small
moths (Figs 7, 12, 13; Tables 1, 2).
Cursorial predation by females versus cursorial predation
males
In tests with vestigial winged fruitflies, normal winged fruitflies and large
moths, the capture efficiencies of females were greater than those of males (Figs
R. K. JACKSON AND M. B. WILLEY
94
70
0
H
1
Female
Male
1
Tap
Pursuit Tendency Capture Efficiency
Figure 12. Results from testing Mjwmarachne with small moths (‘small’ defined in Table 4) in the
laboratory. Male-female comparisons all NS.
0
70
60
i
-I
Female
Male
i
Tap
Pursuit Tendency Capture Efficiency
Figure 13. Results from testing Myrmarachne with large moths (‘large’ defined in Table 4) in the
laboratory. Capture efficiency for females greater than for males ( P < 0.001). Male-female
comparisons NS for tap and pursuit.
COMPARATIVE STUDY OF MTRMARACHNE
95
TABLE
6. Tests of cursorial predation using Myrmarachne females. Comparison of results from tests
using different potential prey (tests of independence with Bonferroni adjustments) in which values
for prey in first column exceeds that for prey in columns to right. Number of tests with each type of
prey in parentheses in first column
Tap
Vestigial Winged
Fruitfly (364)
Pursuit
Winged fruitfly ( P < 0.001 j
Housefly ( P < 0.005)
Gnaphosid ( P < 0.005)
Salticid ( P < 0.001)
Small moth ( P < 0.05)
Large moth ( P < 0.01)
Ant ( P < 0.001)
Salticid ( P < 0.001)
Gnaphosid ( P < 0.001)
Salticid (P< 0.001)
Small moth ( P < 0.001)
Large moth ( P < 0.001)
Ant ( P < 0.001)
Winged fruitfly ( P < 0.01)
Housefly ( P < 0.001)
Gnaphosid ( P < 0.001)
Salticid ( P < 0.001)
Housefly (P< 0.001)
Gnaphosid ( P < 0.001)
Salticid ( P < 0.001)
Housefly (147)
Salticid ( P < 0.001)
Gnaphosid ( 7 1)
Salticid ( P< 0.001 j
Salticid ( 156)
Small moth (218)
Salticid ( P < 0.001)
Gnaphosid (P< 0.05)
Salticid (P< 0.001)
Large moth ( P < 0.001)
Ant ( P < 0.001)
Gnaphosid ( P < 0.05)
Salticid ( P < 0,001)
Large moth ( P < 0.005)
Ant ( P < 0.001)
Salticid ( P < 0.01)
Ant ( P < 0.001)
Ant ( P < 0.001)
Salticid ( P < 0.001)
Large moth (217)
Ant ( P < 0.05)
Salticid ( P < 0.001)
Ant ( P < 0.001)
Salticid ( P < 0.001)
Ant (253)
Salticid ( P < 0.001)
Normal Winged
Fruitfly (187)
Capture Efficiency
Ant ( P < 0.001)
Housefly ( P < 0.001)
Gnaphosid ( P < 0.001)
Salticid ( P < 0.001)
Housefly ( P < 0.001)
Gnaphosid ( P < 0.001)
Salticid ( P < 0.001)
7, 8, 13 and Tables 6, 7). Males apparently responded to prey the same way as
females did, but all types of prey tested usually did not let ~yrmarachnemales
approach close enough to tap and those that were tapped usually did not remain
stationary while being tapped. Apparently, the males’s chelicerae were a
handicap because, when Myrmarachne males moved in close and tapped prey,
their long chelicerae were no more than 1-2 mm from the prey being tapped. I n
fact, males’ chelicerae sometimes touched the prey being tapped and, when this
happened, prey rarely remained stationary.
I n tests with normal winged fruitflies, pursuit tendencies and frequencies of
occurrence of tapping of males were greater than those of females (Fig. 8).
However, in tests with salticids, pursuit tendencies and frequencies of occurrence
of tapping of females were greater than those of males (Fig. 11). There was no
obvious explanation for these differences.
Interactions with ants
In the field, small black ants (not identified) were sometimes found in nests
built by Myrmarachne. T h e nests were recognizable as belonging to Myrmarachne
because of the cottony texture of the silk. Sometimes there were eggs of
Myrmarachne, but never spiders, in the nest with the ants.
Myrmarachne and ants were observed interacting in the field on numerous
occasions. Also, casual observations were made in the vicinity of the study sites
R. R. JACKSON AND M. B. WILLEY
96
TABLE
7. Tests of cursorial predation using Myrmuruchne males. Comparisons of results from tests
using different potential prey (tests of independence with Bonferroni adjustments) in which values
for prey in first column exceeds that for prey in column to right. Number of tests with each type of
prey in parentheses in first column
Tap
Vestigial Winged
Fruitfly (2481
Housefly ( P < 0.001)
Salticid ( P < 0.001)
Large moth ( P < 0.05)
Ant ( P < 0.001)
Normal Winged
Fruitfly (199)
Housefly ( P < 0.005)
Salticid ( P < 0.001 j
Ant ( P < 0.001)
Housefly (72)
Salticid ( P < 0.001)
Gnnphosid (74)
Salticid ( P < 0.001)
Salticid (158)
Small moth (193)
Large moth (215:
Ant (277)
Housefly ( P < 0.05)
Salticid ( P < 0.001)
Ant ( P < 0.001)
Salticid ( P < 0.001)
Ant ( P < 0.001 j
Salticid ( P < 0.001)
Pursuit
Capture Efficiency
~
_
_
_
Winged Fruitfly ( P < 0.001)
Gnaphosid ( P < 0.05)
Salticid ( P < 0.001)
Housefly ( P < 0.001)
Large moth ( P < 0.001) Gnaphosid ( P < 0.001 1
Ant ( P < 0.001)
Salticid cP < 0.001)
Large moth ( P < 0.005)
Housefly ( P < 0.05)
Housefly ( P < 0.05)
Gnaphosid ( P < 0.001)
Salticid ( P < 0,001)
Small moth ( P < 0.005)
Large moth ( P < 0.001)
Ant ( P < 0.001)
Salticid ( P < 0.001)
Ant ( P < 0.001)
Salticid ( P i 0.001)
Ant ( P < 0.001)
Ant ( P < 0.001)
Salticid ( P < 0.001)
Winged Fruitfly ( P < 0.001)
Ant ( P < 0.001 j
Housefly ( P < 0.001)
Gnaphosid (P < 0.001)
Salticid ( P < 0.005)
Large moth ( P < 0.005)
Salticid ( P < 0.001 j
Housefly ( P < 0.01)
Ant ( P < 0.001)
Gnaphosid ( P < 0.05)
by putting ants of various, undetermined species together with Myrmarachne in
cages. The Myrmarachne and ants tested together in these instances were always
sympatric species. However, additional observations were made of Myrmarachne
interacting with New Zealand ants in the laboratory (Table 2 ) .
Myrmarachne usually kept moving so as to remain several body lengths away
from ants. If, apparently by chance, contact was made with an ant, Myrmarachne
usually tapped it. However, no Myrmarachne was seen attacking an ant. While
being tapped, ants usually waved their antennae up and down. Sometimes, the
ant and spider simultaneously tapped each other. However, ants were never
observed to attack Myrmarachne. Sometimes a Myrmarachne and an ant tapped
each other for as long as 10 s, but they usually parted company after c. 0.1 s.
There were no apparent intersexual differences in Myrmarachne’s responses to
ants. In particular, during laboratory tests, there were no evident differences in
the tendencies of males and females to tap ants (females tapped ants in 45O4, of
the tests, males in 390/,, NS).
Responses of Myrmarachne adults to nests and eggs o f other spiders
Adults (females & males) and juveniles ( 3 mm in body length) were tested
with nests of cursorial spiders (Table 2). When a Myrmarachne contacted a nest
(seemingly by accident), it sometimes paused for c.1 s then spread its chelicerae
apart and inserted its fangs in the silk. No oriented walking toward the nest or
any other response from a distance to the nest was evident.
COMPARATIVE STUDY OF MYRMARACHNE
97
TABLE
8. Sample sizes for tests of Myrmarachne with salticid nests
Unattended eggs
Attended eggs
Unattended nest, no eggs
Male
Female
Juvenile
171
163
92
253
185
132
211
209
158
If a nest contained eggs, but no spider (‘unattended eggs’, Table 8),
Myrmarachne sometimes ate the eggs. Myrmarachne adults usually stood on the
nest, salivated and chewed on the silk until making a hole, then placed their
chelicerae over the egg masses and fed. Myrmarachne juveniles usually entered
nests via the doors, then stood over the eggs inside the nest, opened up the eggsac
and fed on the eggs one a t a time. It took Myrmarachne anywhere from 0.5 min to
c 1 h to reach the eggs.
Myrmarachne was also inclined to ‘respond’ (i.e. either open up the nest or enter
the nest via a door) when the nest was unoccupied (i.e. if it contained neither a
spider nor any eggs). There was no evidence, for females, males or juveniles, that
Myrmarachne responded any more or less often to these nests than to unattended
nests containing eggs (Fig. 14).
Females and juveniles each more often responded to unattended nests with
eggs than to attended nests with eggs (P<O.OOl for each), but there was no
evidence that males responded more often to unattended than to attended nests
with eggs.
35
40
+-‘
c
30
25
11
0
1
Attended Eggs
Unattended Eggs
Unattended Nest, No Eggs
Q)
2
20
a
a
15
10
5
0
Female
Male
Juvenile
Figure 14. Results from testing Myrmarachne with salticid nests in the laboratory. Percentage of tests
in which Myrmarachne responded is given for each category of nest and summarized separately for
females, males & juveniles. ‘Responded’: Myrmarachne either made a hole in the nest or entered nest
via door (see text). For sample size, see Table 3.
98
R. R.JACKSON AND M. B. WILLEY
Adult females in nests with eggs (‘attended eggs’, Table 8) usually became
agitated (pulled on the silk, turned about, etc) when a Myrmarachne was on their
nest, especially if Myrmarachne was chewing on the nest silk. Myrmarachne
responded to the resident’s agitation by walking a short distance away then
returning, often doing so repeatedly over a period as long as 20 min. Two sizes of
resident spiders were used in these tests, ‘large’ and ‘small’ (see Table 4); about
half the tests with each sex-age class of each species of Myrmarachne were
conducted with each size of resident spider. Large resident spiders often attacked
Myrmarachne by ( 1 ) immediately striking, (2) running toward (‘charging’), then
striking at, or (3) simply charging, then suddenly stopping in front of,
Myrmarachne. After being attacked, Myrmarachne always left and stayed away
from the nest. The spider struck by lifting its forelegs, then rapidly and forcefully
lowering them onto Myrmarachne or the substrate in front of Myrmarachne. (For a
detailed description of striking and of charging, see Jackson, 1982).
Small spiders rarely charged or struck at Myrmarachne, and when they did,
Myrmarachne usually stood its ground. If the resident female was small,
Myrmarachne sometimes remained for several minutes to over an hour a t the nest;
during this time, Myrmarachne chewed intermittently on the nest silk, and if the
resident spider eventually left, then the Myrmarachne ate the eggs.
There was no evidence that the number of tests in which females responded to
empty nests (unattended nests, no eggs, Table 8) differed from the numbers of
tests in which males or juveniles responded to empty nests. However, juveniles
responded to this kind of nest more often than males did (P<O.O05). Also, there
was no evidence that the number of tests in which females responded to either
attended or unattended nests that contained eggs differed from the numbers of
tests in which males or juveniles responded to these kinds of nests, nor was there
evidence that juveniles differed from males in how often they responded to these
kinds of nests. Myrmarachne that responded to nests that contained egss did not
always eat the eggs. Males (P<O.Ol) and juveniles (P<0.005) each ate eggs
more often in tests with unattended than with attended eggs (Fig. 15). The
figures for females are in the same direction as those for males and juveniles, but
they do not differ significantly. There was no evidence that the different sex-age
classes of Myrmarachne differed in how often they ate eggs for either attended or
unattended nests.
DISCUSSION
Mimicry
Resemblance to ants seems to be achieved by behaviour as well as
morphology. All Myrmarachne studied were found to have an ant-like style of
locomotion. Also, there appear to be match-ups between the appearance of
different species of Myrmarachne and the particular ants present in their habitats
(Edmunds, 1974; Jackson, unpubl. data), but detailed studies in the field are
needed.
Resemblance to ants by IClylmarachne probably functions as Batesian mimicry
(Edmunds, 1974). Ants are well equipped to defend themselves against many
predators (Curio, 1976; Holldobler & Wilson, 1991). Probably, many potential
predators that would eat salticids, but are adverse to eating ants, mistake
COMPARATIVE STUDY OF MTRMARACHNE
*O
15
1
0
99
AttendedEggs
Unattended Eggs
-
w
c
a,
2
10
a,
a
-
5 -
0 -
Female
Male
Juvenile
Figure 15. Results from testing Myrmarachne with salticid nests in the laboratory. Percentage of tests
in which Myrmarachne ate eggs given for each category of nest and summarized separately for
females, males & juveniles.
Myrmarachne for ants and, therefore, fail to attack these salticids (Englehardt,
1970; Cutler, 1992). Experimental work is needed to clarify what cues are
important in ant recognition by the predator and predator deception by the
salticid.
We found no evidence that resemblance to ants assists Myrmarachne in preying
on ants (also see Edmunds, 1974, 1978). I n fact, we found no evidence that ants
are an important prey for these ant-like salticids: Myrmarachne never attacked
ants in the laboratory, and ants were not among the prey records for
Myrmarachne in nature.
It is interesting that, besides failing to see Myrmarachne attack ants, we also
failed to see ants attack Myrmarachne. This suggests that ant mimicry may elicit a
degree of tolerance of the spider by ants. Experimental work might clarify
whether this is so. The manner in which all Myrmarachne species studied tapped
ants with their forelegs, being a t least superficially similar to how ants tap each
other with their antennae, is particularly interesting and should be investigated
experimentally. Also, the possibility that Myrmarachne chemically mimics ants
should be investigated.
Cursorial predation
Myrmarachne’s unusual predatory sequences (run up to the prey, tap rapidly
with legs I, then attack by lunging rather than leaping) appear to be especially
appropriate for an ant-mimicking salticid because, by adopting this style of
predation, prey can usually be captured with only minor disruption of the
spider’s ant-like walking gait. Myrmarachne’s behaviour of usually tapping prey
100
R. R. JACKSON AND M. B. WILLEY
before attacking is particularly atypical predatory behaviour for a salticid, but
consistent with Myrmarachne’s resemblance to ants. Ants tend to tap each other
and other animals with their antennae, and Myrmarachne’s behaviour of tapping
its prey might be important for Myrmarachne in maintenance of Batesian mimicry
during predatory sequences: if Myrmarachne did not tap its prey, Myrmarachne’s
own predators might more readily recognize the Myrmarachne as prey. However,
is there a cost? Does tapping alert potential prey? Does tapping give prey an
opportunity to flee before being attacked?
How serious this disadvantage of warning the prey might be to Myrmarachne
probably varies considerably depending on the type of prey, and this may have
influenced Myrmarachne’s diet in nature. Myrmarachne apparently feeds on a wide
range of arthropod prey in nature, and was observed catching a variety of prey
in the laboratory. I n the laboratory, however, Myrmarachne was more efficient at
catching moths (insects that are slow to take flight) and vestigial winged fruitflies
(flightless and relatively slow-moving insects), and less efficient at catching
houseflies and normal winged fruitflies (highly motile insects). Also, moths were
common in the prey records from nature.
Interestingly, we observed that moths, vestigial winged fruitflies and even
salticids sometimes stayed more or less stationary when tapped by Myrmarachne.
Why these prey of Myrmarachne stayed in place long enough for Myrmarachne to
attack is unclear. However, these observations illustrate that tapping does not
always appear to handicap Myrmarachne during predatory sequences.
Oophasy
Spider eggs are usually enclosed in silk egg sacs, and only a few salticid species
are known to open up other spiders’ egg sacs (Jackson, 1986b; Jackson & Hallas,
1986). Data from nature and the laboratory suggest that eating the eggs of other
spiders, especially salticid eggs, is an important, widespread feeding method in
the genus Myrmarachne. However, it was not clear in all instances from the field
that feeding on eggs was the primary explanation for finding Myrmarachne in
alien nests. I n some instances, Myrmarachne may have been occupying the nest as
a shelter rather than seeking food. For ant-like salticids to enter alien nests and
feed on eggs appears to be consistent with Batesian mimicry because ants in
nature frequent abandoned salticid nests, including nests of Myrmarachne
(Jackson, unpubl. data).
Use of alien webs as nest sites
Occupancy of other spiders’ webs appears to be a regular feature in
Myrmarachne’s natural history. Besides Myrmarachne,there are other salticids that
make a regular practice of invading alien webs (Jackson & Hallas, 1986;
Jackson, 1986b, 1992), but the other web-invading salticids that have been
studied in detail are known to feed on the resident spider. In contrast, there is no
evidence that araneophagy is an important component of Myrmarac~ne’swebinvasion behaviour.
Many potential predators of Myrmarachne may find entry into a web aversive,
suggesting that the primary significance of web invasion of Myrmarchne might be
to gain safety from predators. However, our observation of apparently eaten
COMPARATIVE STUDY OF MYRMARACHNE
101
Myrmarachne in webs suggests that there may be a tradeoff between advantages of
web invasion and vulnerability to attack by the resident spider.
Residency in alien webs appears consistent with Myrmarachne’s resemblance to
ants. Ants have frequently been seen moving about on detritus, and sometimes
on the silk, in spider webs in nature (Jackson, unpubl. data), suggesting that
Myrmarachne can practise web invasion with minimal sacrifice of its resemblance
to ants.
Male versus female predulory behaviour
The large size of the chelicerae of Myrmarachne males is probably an
adaptation related to male-male aggression and sexual selection (see Jackson,
1986a), but there appears to be a trade-off related to predation. I n our
laboratory studies, Myrmarachne males were less efficient than females a t
practising cursorial predation, and the male’s large chelicerae appeared to be a
primary cause of the intersexual differences in prey-catching success.
However, there was no apparent disadvantage of the male’s large chelicerae
when practising oophagy. I n fact, the male’s large chelicerae might be an asset
when removing silk from egg sacs and reaching into the nest for the eggs. Further
studies are needed to investigate whether males in nature practise oophagy more
than females.
Relationship between mimicry and predatory behaviour
Despite ant-like appearance, Myrmarachne performs most of the basic
behaviours common to salticids, including catching insect prey and taking
shelter in nests. Some of Myrmarachne’s behaviours are unusual for salticids, yet
remarkably consistent within the genus. I t appears that the unusual features of
the predatory and nesting behaviour of Myrmarachne are consistent with enabling
these spiders to preserve their ant-like appearance.
Generalizations about the genus Myrmarachne
Myrmarchne is a large genus of salticids. I n addition to in excess of 160
described species, there are no doubt many more yet to be named. Our
generalizations about the genus are based on data from only 31 species, which is
risky. Additional species should be investigated. However, the remarkable
consistency we found in the behaviour of the 31 species we studied suggests
uniformity within the genus for the behavioural characteristics we have
discussed.
ACKNOWLEDGEMENTS
Special thanks are extended to Roy Bulner and Cecil Glanville for their help
with field work in Sri Lanka and to Fred Wanless (British Museum of Natural
History, London) for valuable discussions and his enthusiastic interest in this
project. We gratefully acknowledge Fred Wanless and G. B. Edwards (Florida
Collection of Arthropods) for taxonomic assistance, without which this study
would not have been possible. We thank Phil Taylor for useful discussions about
~.
was
the work and for his critical reading of the manuscript. Financial support
102
R R. JACKSON AND M. B. WILLEY
provided by grants from the National Geographic Society (3226-85) and the
U.S.-New Zealand Cooperative Program of the National Science Foundation
(NSF Grant BNS 8617078). Import permits were provided by the New Zealand
Ministry of Agriculture and Fisheries, and voucher specimens were deposited
with the British Museum (Natural History) and with the Florida Collection of
Arthropods. We are grateful for the assistance of the Department of Wildlife
Conservation in Sri Lanka and the Office of the President of Kenya.
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