14 



BRITISH BUTTERFLIES. 



speeies inhabiting the two hemispheres must have been entirely sepa- 

 rated for a vast period of time. Thus Scudder, writing of this 

 same subject, illustrates his remarks by reference to certain Poly- 

 gonia species, Pieris rapae and Euvanessa antiopa. He says (Butts. 

 New England, i., pp. 672-3) : " Among our American butterflies there 

 is nearly every gradation, from brief and partial companionship up 

 to a social life, which lasts throughout the entire period of larval 

 existence. The weakest form of social life is found in the larvae of 

 some of the species of Polygonia (others being purely solitary), where 

 the eggs, being often laid in columns of two to nine, or , several eggs 

 being scattered by the mother upon one leaf, the caterpillars in earliest 

 life are, naturally, found feeding upon one leaf. Karely are more than 

 four or five found in company, and each takes up its independent 

 position upon the leaf and acts as if the others were not present. As, 

 however, it is their habit to remain upon the leaf until it is almost 

 eaten, they naturally leave it at the same, or nearly the same, time, 

 and, following a similar instinct, are apt to pass together to the 

 nearest leaf, but scatter more or less, so that, by degrees, as they 

 approach maturity, they are found widely separated from each other. 

 Yet, even in this weakest form, their numbers are often so great upon 

 a single plant, that, when they leave it for pupation, the chrysalids 

 hang almost in company, thirty or forty spinning their silken shrouds 

 in such proximity, that they may be pulled down together. A some- 

 what similar, or perhaps weaker, case may be found in Pieris rapae, 

 which often lays a considerable number of eggs, singly, upon one 

 plant, and the caterpillars, naturally, seeking the interior of the 

 cabbage-head, * may often be found in close proximity. But this, 

 even more than the preceding, is a case of mere accident, from the 

 nature of the foodplant upon which they subsist.! In all other cases 

 of social life among our caterpillars, the eggs are laidjby the parent in 

 decided clusters. The slightest of these is probably 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 towards 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 

 foodplant is exceptionally large." He further notes that, so far as the 

 New England fauna is concerned, the great mass of social caterpillars 

 are found in the Nymphalids, and that, " as in Laertias philenor s the 

 larvae of some species, in early life, live exposed upon the surface, 

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

 and sleeping in unison, but, in most cases, some sort of web is con- 

 structed by the caterpillars, upon, or beneath, which they live, and to 

 which, should they wander beyond their haunts for food, they retire 

 for rest and moulting. Some use this web, with certain alterations in 



* Is this really an explanation ? We have seen three or four large fullfed 

 larva; lying side by side on each of several exposed nasturtium (Tropacolum) leaves, 

 on a plant climbing up a lattice. 



( Nor do we think this is a sound explanation, as, in this country, at least, the 

 habit is maintained on several foodplants widely different from cabbage in then- 

 manner of growth. 



