THE GREGARIOUS HABIT IN BUTTERFLY LARVAE. 



21 



dark grapes from the already bare and leafless twigs, only separating 

 finally for the purpose of pupation. 



Somewhat similar to these are the habits of larvae of Araschnia 

 levana, which Roesel describes at length (Ins. Belustigung, i., pt. 1, 

 p. 50), noting that they feed on the great stinging-nettle, and are not 

 to be found on those clumps growing in open fields, but in woods and 

 gardens, growing in the shade. He observes that, not only are the 

 eggs laid in groups (or strings, one egg placed on the other), on the 

 underside of a nettle-leaf, but the larvse of each batch keep constantly 

 together from the time of hatching up to very nearly the time of pupa- 

 tion. As soon as the larvae have left the eggshells, the whole batch covers 

 itself with a whitish-grey web, under which the caterpillars remain 

 together until their store of food runs out, when, of necessity, they 

 have to seek pastures new ; at this time they also undergo their first 

 moult, leaving their cast skins in the old web, and change from the 

 shining dark brown unspined, to a much more markedly spined, form. 

 As soon as they have selected a fresh pasture-ground, they surround 

 themselves with a new, though rather looser, web, and so continue 

 until nearly fullgrown, when the largest amongst them scarcely attain 

 lin. in length. 



Of the most strikingly gregarious butterfly larvae discovered, it is 

 unfortunate that so little is really known. One of the most remarkable 

 of these is Eucheira socialis, a Mexican Pierine, whose wonderful larval 

 nest appears first to have been described by Hardy (Travels in the 

 interior of Mexico), Westwood (Trans. Ent. Soc. Lond., 1836, p. 38), 

 etc. Dixey strangely hazards the opinion (Trans. Ent. Soc. Lond., 

 1894, p. 303) that the common larval habitations are a sign of affinity 

 between Aporia (crataegi) and Eucheira (socialis), stating that that of the 

 former, " though merely rudimentary, and belonging only to the early 

 larval stages, is no doubt a degenerate or undeveloped form of the 

 elaborate silken nest constructed by E. socialis." We should state this 

 in exactly opposite terms, and suppose that that of Eucheira socialis 

 was a highly-developed form of the social nest, towards which that of 

 Aporia crataegi already showed some tendency to approach, for there 

 can be no doubt that the ancestral Pierid larva was solitary. It is, 

 indeed, rare for the larval social habits to be carried so far as is the 

 case in E. socialis, for, according to Holland (Proc. Ent. Soc. Lond., 1905, 

 pp. xxi-xxii), the larvae remain within the nest when quite fullfed, 

 pupating therein, and the imagines even (at least sometimes) lay their 

 eggs within the social habitation. Strangely enough, the larvae 

 suspend themselves, Nymphalid-like, by the tails, for pupation, and not 

 as do normal Pierids, by means of an anal pad and silken girth. 

 Holland further notes (op. cit.) that Lumholz figures a group of 

 Mexican Indians engaged in extracting the caterpillars from the silken 

 tents, the former being a staple article of diet among some of the 

 mountain tribes, whilst he adds that the forests, in places, are literally 

 white with the big silken webs, many of which are five or six times 

 greater than the original specimen described and figured by Westwood. 

 It would appear that somewhat similar webs are made by the larvae of 

 Neophasia terlootii (Behr, Trans. Amer. Ent. Soc, 1869, p. 303 ; Proc. 

 Calif. Acad. Sci., 2nd series, ii., p. 91), for Behr says that the larvae of 

 this species are very common in Mexico and Arizona, on Arbutus, and 

 form common habitations, in which they pupate gregariously. As 



