130 SOCIAL CATERPILLARS 



cabbage-head, may often be found in close prox- 

 imity. But this even more than the preceding is 

 a case of mere accident, from the nature of the 

 food-plant upon which they subsist. In all other 

 cases of social life among our caterpillars the eggs 

 are laid by the parent in decided clusters. The 

 slightest of these is probably that of the Blue 

 Swallow-tail (Laertias philenor) the masses being 

 ordinarily confined to a dozen or so. The cater- 

 pillars in this case not only feed in company but, 

 in earliest life at least, range in rows along the 

 edge of the leaf they are eating, with their heads 

 toward the eaten portion ; and in this way they 

 live during at least the earlier half of their lives, 

 scattering more or less after the third moult upon 

 separate leaves, so that at maturity rarely more 

 than one is found upon a single leaf, though the 

 leaf of their food-j^lant is exceptionally large. 



This alteration of habit from companionship to 

 solitariness is a natural incident due to growth. 

 Up to the end of the third moult the size of the 

 caterpillar has not increased enough to make it a 

 conspicuous object, but by the time the third moult 

 is passed the caterpillar is half grown, and during 

 this stage and the next its size becomes an impor- 

 tant element in its security ; and this alone is suffi- 



