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Psyche 
[September-December 
the silk lines of araneid webs. They conclude that the moth gains 
protection by the association. In this paper I describe the associa- 
tion between larvae of the noctuid moth Neopalthis madates Druce 
and the colonial spider Anelosimus eximius Simon. In addition, 
three other instances of associations between lepidopteran larvae 
and web-building spiders are briefly reported. These involve the 
araneid Cyrtophora nympha Simon, an undetermined diplurid and 
an undetermined social theridiid in Papua New Guinea. The rela- 
tionship between Neopalthis larvae and A. eximius is a symbiosis 
that primarily involves scavenging but may occasionally involve 
the loss to the spider of usable food resources. Thus the symbiosis 
is probably commensal for the most part but sometimes (or poten- 
tially) deleterious. The terminology of symbioses for such “border- 
line” cases is in a currently unsatisfactory state. 
The Neopalthis/ Anelosimus Symbiosis 
The nature of the symbiosis can only be understood if some de- 
tails of the biology of Anelosimus eximius are given. There have 
been a number of notes on aspects of the biology of this species 
(e.g., Levi, 1955; Brach, 1975) and it is currently under study at 
the Smithsonian Tropical Research Institute (by Dr. F. Vollrath). 
The following notes are based on my own studies and those of 
Vollrath (pers. comm.). Anelosimus eximius webs are built and 
occupied by a variable number of spiders, from less than a hundred 
to at least several thousand. They may persist in one place for many 
years. One on Barro Colorado Island, Canal Zone, was in the same 
tree from 1965 to 1971. Colonies may reach striking proportions, 
occupying many cubic meters of space. Essentially all webs have 
a simple basic structure. The lower web consists of a continuous 
sheet of silk that is concave and often basin-like, being raised at its 
periphery. Above this and partly attached to it is an aerial snare 
of threads that are preponderantly oriented more or less perpen- 
dicular to the sheet. This is the part that is the effective prey-capture 
structure. The spiders attack prey within the aerial snare and on 
the basal sheet. Since the basic web is persistent for long periods, 
it acquires a litter of plant debris and prey remains. (In captivity 
the spiders seem to indulge in occasional web-cleaning bouts and 
carry prey remains to the edge of the web where they are tipped 
out.) 
