SYMBIOSES BETWEEN INSECTS AND SPIDERS: 
AN ASSOCIATION BETWEEN LEPIDOPTERAN LARVAE 
AND THE SOCIAL SPIDER ANELOSIMUS EXIMIUS 
(ARANEAE: THERIDIIDAE)* 
By Michael H. Robinson 
Smithsonian Tropical Research Institute 
P.O. Box 2072, Balboa, Canal Zone, Panama 
Introduction 
There are many instances of relationships between insects and 
spiders that are not simply relationships between predators and 
prey. Bristowe (1941) cites numerous examples either from his own 
extensive experience or from a broad review of the diverse litera- 
ture. Moths have been reported to associate with spiders’ webs 
both as adults and larvae. Thus Pocock (1903) reported a case of 
commensalism between the gregarious spider Stegodyphus sp. (Eri- 
sidae) and the moth Batrachedra stegodyphobius Walsingham. The 
unnamed species of Stegodyphus from South Africa had small lepi- 
dopteran larvae crawling about within the communal web. These 
fed upon “the carcases of the flies or other insects which, with in- 
finite labour and patience, the spiders hauled up as near their nest 
as possible. . . .” Pocock states that pupation occurred within the 
nest (= web) and that, after emergence, adult moths moved about 
the web walking, leaping and fluttering. Reportedly the moths did 
not get caught in the sticky (cribellate) silk “being gifted apparently, 
like the spiders themselves, with some safeguard against the sticki- 
ness of the threads, which proved so fatal to other insects” (1903: 
169). Brach (1977) reports that the webs of Anelosimus studiosus, 
in Florida are shared by a host of other arthropods including py- 
ralid “webworms.” He comments that the relationship between 
these other arthropods and the Anelosimus is not clear, but that 
the majority “are found in the periphery of senescent webs and 
may be physically isolated from contact with colony members by 
their own silken retreats” (1977:155). Robinson and Robinson 
(1976:12-16) report on a pyralid moth that, as an adult, rests on 
* Manuscript received by the editor April 27, 1978 
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