THE PROCESSIONARY MOTH . 
367 
Externally it is not unlike that of the brown-tailed moth, but 
it differs in one respect, namely, that it is not divided into 
separate chambers, and has only one aperture. When the larvae 
sally out for the purpose of procuring food, they spin guide 
lines, as is the case with many other caterpillars. But, instead of 
going out singly into the world, each to find its own food in its 
own way, they march out in regular order, like a military party 
on a foraging expedition. 
A single caterpillar is always the leader, and often is followed 
by one or two others in Indian file. Presently, however, the 
caterpillars march two deep, and, if a large number should be on 
the move, the line is sometimes from five to six deep. They are 
all very close to each other, so that the procession flows on in 
one unbroken line, and until the observer is close to it, he can- 
not see that its component parts are moving at all. 
The reader may remember that two species of wasp, namely 
Vespa vulgaris and Vespa germanica, will work harmoniously at 
the same nest. This curious sociability, which is contrary to the 
usual custom of nature, is shared by moths as well as wasps. When 
experimenting upon the nests of this species, M. Reaumur found 
that several distinct broods of caterpillars would spin a common 
web and live in peace together, just as if they had been the off- 
spring of one mother. Mr. Rennie, however, carried the experi- 
ments still farther, and found that two different species would 
act in the same social manner. 
4 We ourselves ascertained during the present summer (1829) 
that this principle of sociality is not confined to the same 
species, or even to the same genus. The experiment which we 
tried was, to confine two broods of different species to the same 
branch, by placing it in a glass of water to prevent their escape. 
The caterpillars which we experimented upon were several 
broods of the brown-tail moth ( Porthesia auriflud) and the 
lackey ( Clisiocampa neustrio). These we found to work with as 
much industry and harmony in constructing their common tent 
as if they had been at liberty in their native trees ; and when 
the lackeys encountered the brown tails they manifested no 
