A Description of an Unusual Dome Web Occupied by Egg-Carrying Holocnemus pluchei (Araneae, Pholcidae)

4 Pages·1998·3.4 MB·English

by  Kris A Sedey

1998. The Journal of Arachnology 26:385-388
RESEARCH NOTE
A DESCRIPTION OF AN UNUSUAL DOME WEB OCCUPIED BY
EGG-CARRYING HOLOCNEMUS PLUCHEI
(ARANEAE, PHOLCIDAE)
Spiders use silk to construct prey-capture Each web was numbered with masking tape
webs, protective tubes and retreats, and egg adjacent to the web. Dome diameters were
sacs (reviewed in Nentwig & Heimer 1987). measured with a 10 cm ruler. Activity of fe-
Holocnemus pluchei (Scopoli 1763) build ir- males in the domes and of associated spiders
regular, often curved prey-capture sheets, and, was noted before and after the application of a
like other pholcids, hold their eggs in a loose tuning forkto the web. Behaviorpatterns noted
bundle in their chelicerae. Egg-carrying H. were: approaching orwrapping the tuning fork,
pluchei are found inside unusual dome-shaped considered to be predatory behaviors; bounc-
webs that are easily distinguishable from the ing, a rapid up-and-down movement whichhas
normal prey-capture web. Dome webs are gen- been shown to be an anti-predator response
erally spherical, completely surrounding the fe- (Jackson et al. 1993); or no response. Webs
male and her eggs, and attached to structures were revisited the next day.
such as buildings or the stiffinner branches of Domes averaged 5.04 cm in diameter (SE
bushes. After the eggs hatch, the female leaves = 1.33) (Fig. 1). Nineteen were on the ceiling
the dome. Spiderlings remain in the dome until and five were in the comer formed by the ceil-
their first molt. After molting, they disperse ing and the walk Fifteen were complete
and either construct a sheet web or join the domes with no damage; nine had small holes
webs ofother spiders, where they live together in the side. Domes were composed of fine
on the same sheet (Jakob 1991; unpubl. data). silken strands, with no apparent pattern in
Here we describe dome webs in the field, in- their arrangement. Strands were occasionally
cluding the presence of associated spiders out- clumped into small balls on the surface ofthe
side ofthe domes, and the responses ofspiders dome. We saw no viscid balls, as has been
in-and-near dome webs to the vibration of a noted in another pholcid (Briceno 1985).
tuning fork, which generally elicits a prey-cap- There was at least one conspecific within 15
ture response from H. pluchei spiders on prey- cm of 71% of females in web domes. These
capture sheets (Jakob 1991). associated spiders were not on prey-capture
H. pluchei spiders are abundant in the Cen- webs, but were either resting directly on the
tral Valley of California, and are commonly outside of the dome, on a few silk threads at-
found in bushes, especially junipers (Junip- tached to the building, or on the concrete over-
erus sp.), and around human habitation. Al- hang to which the dome was attached. The
though domes can be found deep within ju- nearest groups of prey-capture webs were on
niper bushes, that location makes them bushes at least 10 m away from the domes de-
difficult to study. Therefore, we focused on scribed here. We have never seen spiders as-
dome webs found under an overhanging out- sociated in the same way with the sheet webs
m
door ceiling, approximately 2 high, of used in prey capture; spiders near sheet webs
Briggs Hall at the University of California at are either in a web themselves or are moving
Davis. Observations were made on 16 and 17 rapidly through the vegetation. We identified
August 1995. classified spiders as mature males, mature fe-
We selected 24 dome webs for study. Nine- males, medium juveniles (probably 4th instar)
teen contained a female with an egg sac in her and small juveniles (2nd or 3rd instar) (repre-
chelicerae and five held a female surrounded sentative measurements of size classes are giv-
by recent hatchlings (first instar spiderlings). en in Jakob 1994). The most common associ-
385
386 THE JOURNAL OF ARACHNOLOGY
—
Figure 1. Female Holocnemuspluchei and eggs, surrounding by a dome web.
ates were males (Table 1). On day 1, most a male; this did not differ significantly from
females with eggs were accompanied by at females with eggs.
least one male (14 of 19), but only one female We compared spiders that were inside
with hatchlings was accompanied by a male; domes, associated with domes, and on prey-
this difference nears statistical significance capture webs. The data on spiders from prey-
(contingency test, “ 3.818, df = 1, P = capture webs came from a survey conducted
0.0507). On the second day, 11 of 19 females in July 1996 (Johnson 1997; Johnson & Jakob
with eggs were accompanied by at least one in press). In that survey, the number and class
male. Only three females with hatchlings were (small juvenile, medium juvenile, adult fe-
located on day 2, and one was accompaniedby male, adult male, and female with eggs or
—
Table 1. Spiders within 15 cm ofthe domes of focal females on consecutive days.
Day 1 Day 2
Females with eggs
1 male 8 8
2 males 2
1 male and 1 female with eggs 2 1
1 male and 1 female with new hatch 1 1
1 female, 1 male, 1 medium, and 2 small 1
1 small 3 2
None 3 6
Total webs with eggs 19 19
Females with hatchlings
1 male and 1 female 1
1 male, 1 female, and 1 small 1
None 4 2
Total webs with hatchlings 5 3
SEDEY & JAKOB—AN UNUSUAL DOME WEB 387
—
Table 2 A comparison ofthe number ofspiders in different sex and age categories that were on prey-
.
capture (sheet) webs, those that were inside domes, and those that were associated with domes on day 1.
Expectedvalues are inparentheses. Differences are significant (x^ = 2173.8, df^ 8, P < 0.0001). Patterns
for day 2 are similar (x^ = 2117.3, df= 8, P < 0.0001). ‘Data from Johnson 1997; Johnson & Jakob in
press.
Associated
Sheet webs* Inside domes with domes
Females with eggs or hatchlings 0 (23.4) 24 (0.3) 0 (0.3)
Females 657 (645.7) 0 (7.8) 4 (7.5)
Males 123 (135.8) 0 (1.6) 16 (1.6)
Mediumjuveniles 763 (745.3) 0 (9.0) 0 (8.6)
Smalljuveniles 439 (431.8) 0 (5.2) 3 (5.0)
hatchlings) of all spiders on 1406 webs were sponse or bounced. Four of five females with
recorded. Methods followed Jakob (1991), hatchlings attempted to wrap the tuning fork
and included touching aringing tuning forkto tip. These data suggest that the prey-capture
the web to attract spiders that mightbe hidden response of the females is suppressed while
by vegetation at the web edge. she is holding eggs in her chelicerae, but re-
We found significant differences in the turns when the eggs have hatched. Associated
classes of spiders that were most likely to be male and juvenile spiders also frequently at-
found on prey-capture webs, inside domes, or tacked the tuning fork (Table 3).
associated with domes (Table 2). Dome webs Our data suggest that male spiders may be
contained more females with eggs or hatch- attracted to females in dome webs, particular-
lings than expected. Associates ofdomes were ly females carrying egg sacs. It is not known
significantly more likely to be adult males whether males are seeking to capture prey by
than expected. As a follow-up test, we also using the dome web, seeking protection from
compared dome associates only to spiders on predators by associating with females in
prey-capture sheets, omitting females with domes, or seeking to copulate with the fe-
eggs or hatchlings. Again, we found a signif- males. The first possibility seems unlikely as
icantly greater proportion of males associated we never saw prey in these small webs. The
with domes than on prey-capture webs (day second possibility is difficult to evaluate, giv-
1: x" = 143.1, df= 3,P < 0.0001; day 2; x" en the lack of evidence of predation in this
- 92.3, df= 3, P < 0.0001). population. It seems most likely thatmales are
Females with eggs and females with hatch- seeking copulations with females: H. pluchei
lings behaved differently in response to the exhibits last-male spermpriority (Kaster& Ja-
tuning fork (x^ = 18.24, df = 1, P < 0.0001, kob 1997), so a female that has already been
Table 3). Females with eggs never exhibited mated would still be valuable to a male. It is
predatory behavior, but instead gave no re- not clear why juvenile or female spiders are
—
Table 3. Responses of focal spiders in dome webs {n = 24) and associated spiders outside of dome
{n ~ 23) webs to a ringing tuning fork.
No response
or slight Approach Wrap
movement Bounce tuning fork tuning fork
Focal female with eggs 15 4
Focal female with hatchlings 1 4
Associated male 2 6 4 4
Associated female 1
Associated female with eggs 1 1
Associated female with hatchlings 1
Juvenile 3
388 THE JOURNAL OF ARACHNOLOGY
found near domes and not on prey-capture LITERATURE CITED
webs. Our data from two consecutive days Briceno, R. 1985. Sticky balls in webs of the spi-
suggests that movements ofassociated spiders der Modisimus sp. (Araneae, Pholcidae). J. Ar-
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of several species in the Pisauridae carry their Fink, L.S. 1986. Costs and benefits ofmaternal be-
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by surrounding herself and her brood with
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of approaching predators more readily. Pro- spider has minimal costs in competitive ability
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e1g9g87;saWcsililneyth&e gArdeleenrl1y9n8x9)s.piAdterth(iFsitnikme1,98w6e, Nenptewcitsg,ofW.spi&derS.weHbesi.mePrp.. 211918-72.25E.coIlnogEiccoaplhyass--
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pluchei because the severity of interspecific Verlag, Berlin.
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native habitat is not known. However, canni- temel de Pisaura mirabilis. Livrejubil. Bouvier,
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ACKNOWLEDGMENTS Kris A. Sedey and Elizabeth M.JakobL De-
partment of Biological Sciences, Bowling
We thank the National Science Foundation Green State University, Bowling Green,
for support (IBN 94-07357 and IBN 95- Ohio 43403 USA
07417), especially for a Research Experience Manuscript received20December1997, revised10
for Undergraduates supplement that funded June 1998.
the fieldwork ofKAS. A. Porter, S. Vessey, G.
Stratton and A. Rypstra provided valuable ^ Current address: Department ofEntomology, Uni-
comments on the manuscript. Thanks to E. versity of Massachusetts, Amherst, Massachusetts
Tani for photographic assistance. 01003 USA.