2007 (2008). The Journal of Arachnology 35:557–560
SHORT COMMUNICATION
CARRION FEEDING BY SPIDERLINGS OF THE COB-WEB SPIDER
THERIDION EVEXUM (ARANEAE, THERIDIIDAE)
Gilbert Barrantes and Ju-Lin Weng1: Escuela de Biologı́a, Ciudad Universitaria Rodrigo
Facio, Universidad de Costa Rica, San Pedro, San José, Costa Rica. E-mail: gilbert.
barrantes@gmail.com
ABSTRACT. The use of carrion to feed spiderlings has never previously been observed in spiders. Here we
show that the theridiid Theridion evexum Keyserling 1884 stored dead insectan prey for up to one week prior
to the emergence of spiderlings from the egg sac, and continued to feed spiderlings dead prey for six weeks
until spiderlings molted to the fourth instar. Spiderlings survived and molted on an experimental diet of
exclusively rotten insects.
Keywords: Diet, rotten insects, spiderlings survivorship, prey choice
Generally, spiders are thought to be obligate carcasses within a few hours. However, frequently
predators that feed on a wide variety of prey females with spiderlings will accumulate several prey
(Bristowe 1958; Foelix 1996). Spiderlings also are items in their retreats (pers. obs.). Observations on
predators once they begin to feed (Foelix 1996; GB feeding behavior and experiments on prey acceptance
unpublished data), although the young of some cob- of T. evexum were made in captivity and in the field,
web spiders (Theridiidae) are fed by their mother from September 2004 to October 2005, in a 2-ha
with freshly caught prey or by regurgitation (Gertsch biological reserve on the campus of the Universidad
1949; Viera et al. 2005). However, numerous de Costa Rica, San Pedro, San José Province, Costa
examples show that, at least occasionally, spiders in Rica (9u549N, 84u039W; elev. 1200 m).
different families feed on carrion (Bristowe 1958; To determine whether spiders feed on carrion, we
Knost & Rovner 1975; Ross 1981; Pekár 2004), and fed them flies in the families Muscidae, Calliphori-
for some spiders carrion seems to be a primary item dae, and Sarcophagidae. Flies were killed by placing
in their diet (Sandidge 2003). The use of carrion to them in a freezer for 20 to 30 min (212u C) and were
feed spiderlings has never previously been observed then immediately placed in a chamber saturated with
in spiders, however. Here, we show that mature water vapor at room temperature (20–22u C) for 40–
females of the theridiid Theridion evexum Keyserling 54 h for field experiments, or 24–63 h for laboratory
1884 begin to store dead prey several days before experiments. After 24 h the muscles of thorax and
spiderlings emerge and that spiderlings can survive legs of the decomposing flies had changed from
and grow on a diet of exclusively rotten prey. a nearly white tissue to a juicy, red-brownish mass
Theridion evexum folds a leaf to form a conical that emanated a pungent ‘‘rotten meat’’ odor. The
retreat, and makes a small tangle just in front the dead insects were stuck to the vertical viscid threads
retreat opening (Barrantes & Weng 2007). Several of the web, which were then vibrated using a tuning
long threads studded with viscid droplets run from fork or forceps. These movements induced the
this tangle to other leaves. Prey trapped on these long spiders to descend and attack the dead insect.
threads are wrapped and carried into the retreat Mature female spiders in captivity were each
where the spider feeds. The egg sac is housed within placed on a hexagonal truncated-pyramidal wire
the retreat. After emerging from the egg sac, frame (20 cm high), with a hexagonal cardboard base
spiderlings remain in the retreat with their mother (7 cm side) to which the spiders anchored their viscid
until they have gone through three or four molts, at threads (Barrantes & Weng 2007). A paper cone at
which time they disperse. Large young spiders (5th the apex of the structure served as the spider retreat.
stage to pre-adult), females without spiderlings, and The frame hung 2 m above the floor from a thin
females with new egg sacs will all discard prey nylon fishing line.
To test survival and growth on a diet of rotten
1 Current address: Department of Entomology, insects, we formed nine treatment groups by dividing
Kansas State University, Manhattan, Kansas 66506 one clutch of each of three females into three groups
USA. of spiderlings that were nearly emerged from the egg
557
558 THE JOURNAL OF ARACHNOLOGY
Figure 1.—Mature female of Theridion evexum in a retreat that has been opened to reveal the egg sac and
the second-instar spiderlings feeding on three dead insects captured two, four, and six days previously.
sac, before they could feed the first time, and placed spiders were deposited in the Museo de Zoologı́a,
each group in a separate petri dish (eight groups had Universidad de Costa Rica.
seven spiderlings, the other group had six). Spider- We additionally fed 23 mature female spiders with
lings did not emerge at the same time from the three decomposing insects in the field. Sixteen of these
egg sacs so experiments were not run at the same spiders had spiderlings, and both the adult and the
time for the nine groups. The three treatments were spiderlings fed on rotten insects (Fig. 1). Two spiders
randomly assigned to the groups; thus one group with egg sacs wrapped the rotten prey and carried
from each clutch was fed rotten insects, the second them to the retreat where they hung until spiderlings
group, freshly killed insects, and the third group was emerged about four days later. The last five females
starved as a control. All insects in this experiment without egg sacs or spiderlings rejected the rotten
were blow flies (Calliphoridae). Moisture in all petri insects. In captivity we fed three mature females that
dishes was provided by a piece of water-soaked had egg sacs, from which spiderlings emerged within
cotton. In the rotten-fly treatment, the dead flies 10 days, exclusively with rotten prey. When these
rotted at room temperature for 24 h as described spiderlings emerged from the egg sac, they and their
previously. Both fresh and rotten flies were pierced mothers were fed exclusively with additional rotten
four times in the thorax, with an entomological pin, insects until some of the spiderlings reached the third
before giving them to the spiderlings. The holes were instar. These females accumulated carrion for
to facilitate spiderling feeding. Mature females with practically six weeks and spiderlings fed on both
spiderlings pierced their prey several times, including very old and newly acquired rotten insects (Fig. 1).
dead insects, before leaving them for spiderlings to Recently emerged spiderlings fed rotten insects
feed upon. We replaced the food for the spiderlings (dead for 24 h) and those fed freshly killed flies
every 24 h and checked for feeding spiderlings three molted twice (experiment ended when all spiderlings
times a day. Instars were counted beginning with either molted twice or died). However, the intermolt
emergence from the egg sac (these spiderlings period to the first molt and to the second molt were
undergo one post-emergent molt inside the egg shorter for spiderlings fed freshly killed insects (first
sac). The intermolt period of the spiderlings to the molt, Fig. 2: F 5 7.12, P 5 0.01, df 5 1, 35; second
first and second molts was analyzed using a Ran- molt: F 5 25.24, P , 0.001, df 5 1, 31). Surprisingly,
domized Complete Block Design. This analysis of all spiderlings (n 5 20) feeding upon carrion
variance allows testing differences among treatments survived, but 28% of the spiderlings feeding on
(rotten vs. freshly killed insects) while subtracting the freshly dead prey (n 5 21) died (Fisher test P 5 0.03).
effect of the block (group). Voucher specimens of the Mortality occurred in all three groups of spiderlings
BARRANTES & WENG—CARRION DIET IN A COB WEB SPIDER 559
Figures 2–3.—Intermolt days to the first (Fig. 2) and second (Fig. 3) molt (mean, standard error and
standard deviation) of spiderlings fed carrion (C) and fresh prey (F), from clutches of three different females.
Sample size is indicated below each subgroup.
fed with fresh-killed flies. All starved spiderlings (n 5 Bristowe (1958) reported Schotophaeus blackwalli
21) died before molting a single time. (Thorell 1871) (Gnaphosidae) feeding on dead
The results on growth and mortality of spiderlings lepidopterans pinned on setting boards. The ant-
indicate that bacteria (or other decomposers) possi- eating specialist spider, Zodarion germanicum (C.L.
bly reduced nutrient quality and/or content of prey, Koch 1837) (Zodariidae), apparently occasionally
as the intermolt period to the first and second molt scavenges on dead ants discarded in the cemetery of
were longer for spiderlings fed rotten insects. ant nests (Pekár 2004). Pholcus phalangiodes (Fues-
However, it is unclear why fresh-killed prey increased slin 1775) (Pholcidae), Nephila clavipes (Linnaeus
mortality of spiderlings. A possible explanation is 1767) (Nephilidae) (G. Uhl and W.G. Eberhard pers.
that bacteria somehow breaks down some proteins comm., respectively) were observed feeding on dead
(or other components) that could be indigestible, at insects hanging for a few days in their webs. Within
least for some spiderlings, thus reducing their Theridiidae, three Latrodectus hesperus Chamberlin
mortality. Yet, further investigation is needed to & Ivie 1935, fed on old dead insects (Ross 1981), and
understand how the changes produced by bacteria in four individuals of Faiditus sp., a kleptoparasite in
the prey reduce spiderlings’ mortality. webs of other spiders (Agnarsson 2003), were
Spiderlings of other theridiid spiders [e.g. Chrysso observed feeding on their dead spider host (N.
cambridgei (Petrunkevitch 1911), Achaearanea tesse- clavipes) for more than 16 days (W.G. Eberhard,
lata (Keyserling 1884) and Anelosimus studiosus pers. com.). Knost & Rovner (1975) experimentally
(Hentz 1850)] fed occasionally on dead prey accu- demonstrated that wolf spiders (Lycosidae) Schizo-
mulated in their webs for up to one week (pers. obs.). cosa ocreata (Hentz 1844) as well as Rabidosa rabida
However, T. evexum is the first spider in which (Walckenaer 1837) and Rabidosa punctulata (Hentz
carrion feeding plays a central role in rearing 1844) scavenged on old-dead insect parts when
offspring since adult females actively save dead prey freshly killed insects were not available, and San-
for their offspring to feed on. At least in T. evexum, didge (2003) described the preference of Loxosceles
C. cambridgei, A.tesselata and A. studiosus the reclusa Gertsch & Mulaik 1940 (Sicariidae) for dead
provision of carrion to spiderlings is likely related over live prey. It is also known that matriphagy,
to the cohabitation of the young spiders with their where spiderlings sometimes feed for several days on
mother for some time. In these cobweb spiders, their dead mother, is common in several spiders:
spiderlings cohabit with their mother in the same Amaurobius sp. (Bristowe 1958) and A. ferox
web, at least to the third molt outside of the egg sac (Walckenaer 1830) (Amaurobiidae) (Kim et al.
(pers. obs.). Saving old dead prey may assure food 2000), Stegodyphus lineatus (Latreille 1817) (Eresi-
provision for spiderlings and may be advantageous dae), and occasionally in A. tesselata (Theridiidae)
for maternal spiders as prey is usually unpredictable (pers. obs.). This fragmentary information on scav-
in time (Wise 1982). It is possible that the use of enging and matriphagy on a wide, phylogeneticaly
carrion for adult spiders and as provision for unrelated range of spiders (Coddington 2005) in-
spiderlings may be more frequent when live prey dicate that, at least occasionally, carrion feeding is
are scarce, as suggested by Knost & Rovner (1975) widespread among spiders.
for wolf spiders. We thank W.G. Eberhard, D.H. Wise, G. Strat-
Spiders of different families have occasionally been ton, and two anonymous reviewers for helpful
observed feeding on dead insects. For instance, comments on the manuscript; and W.G. Eberhard
560 THE JOURNAL OF ARACHNOLOGY
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carrion feeding. I. Agnarsson kindly identified the value of matriphagy in the spider Amaurobius
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