SOCIAL CATERPILLARS 131 



cient to account for the fact that mature cater- 

 pillars of butterflies are rarely found in company. 

 It is at this stage, too, that in many instances, the 

 winter season overtakes the caterpillar and it hiber- 

 nates ; and since in the spring it revives when the 

 plants have put forth but tender leaves, impossible 

 to nourish more than one or at most two such 

 ravenous beasts as now come out of their winter 

 quarters, such a change of habit would seem to be 

 compulsory. Possibly the change in habit which 

 generally takes place at this middle period of 

 caterpillar life, even when winter does not intervene, 

 is an inheritance from a common ancestor whose 

 habits were fixed by the necessity of hibernation 

 at this age. 



As far as our own fauna is concerned, the great 

 mass of social caterpillars are found in the high- 

 est family, the Nymphalidae, and indeed in the 

 sub-family, Nymphalinae, in which this habit is 

 found in most of the principal groups. In some 

 instances, as we have related of the Blue Swallow- 

 tail (Laertias philenor), the caterpillars in early 

 Hfe live exposed upon the surface, generally the 

 under surface, of the leaf, ranged side by side, 

 feeding and sleeping in unison. But in most some 

 sort of web is constructed by the caterpillars upon 



