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 hne 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. 



'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 difi'erent 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 (Forthesia auriflua) and the 

 lackey (Clisiocampa neustria). 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 



