1977] 
Robinson — Insects and Spiders 
227 
I found the first caterpillars in an Anelosimus colony in January 
1976. A small colony of less than one hundred individuals was 
collected from Cerro Galera, Canal Zone, Panama, and taken into 
the laboratory for behavioral studies. The collection was made by 
bagging the entire colony on the branch of a tree and then cutting 
off the branch. This was then set up in a cage. The colony was 
thus collected intact and complete with all spiders, debris, and 
inquilines. After some period of observations on the spiders, the 
caterpillars were seen. There appeared to be several of these; at 
least two were seen at one time, and eventually four pupae were 
recovered from the web. When not actively feeding, the caterpillars 
rested beneath the plant debris in the web or stretched out in stick- 
like postures. Feeding on insect remains was seen both by day and 
by night. Movement within the web seemed to be purposively 
towards prey remains rather than exploratory, but this proved 
difficult to quantify since the caterpillars had to weave their bodies 
in and out of the maze-like strands of the snare. In an attempt to 
investigate the possible cues used by the caterpillars in finding their 
food, I excised a section of the web away from a spider aggregation 
and put two caterpillars in this. (Cutting sections of spider web is 
easy, a hot soldering iron or glowing tip of a lighted cigarette cuts 
the silk with little pressure.) In this spider-free web I placed a 
freshly killed tettigoniid (Orthoptera) of about 100 mg weight. The 
caterpillars made no immediate move towards the katydid, but 
some hours later both were feeding on it and one was almost inside 
the body of the dead insect. Figure 1 shows a caterpillar in action. 
Clearly the caterpillars could feed on an entire insect as well as on 
exoskeletal fragments. They may well do this in the natural situa- 
tion. Both caterpillars pupated the morning following this massive 
meal and this ended the investigation. Caterpillars have been found 
in other Anelosimus eximius colonies by me and by F. Vollrath 
(pers. comm.). Vollrath raised Neopalthis madates from his cater- 
pillars and also another moth species that was clearly not a noctuid. 
This species has not been determined. It is entirely possible that 
still other species of lepidoptera could be involved in this kind of 
symbiosis with Anelosimus eximius; this matter is discussed later. 
Further investigation of the relationship awaits a situation where 
infested colonies are abundant and can be subjected to traumatic 
or destructive experimentation. 
