58 



BRITISH BUTTERFLIES. 



purpose, but the result of journeying to the nearest leaves to feed and 

 returning to the central position for resting. They appear often to 

 feed in turns, one lot going out to feed whilst others have just 

 returned to rest. As they get larger they move their headquarters, 

 again, apparently, according to such exigencies as may occur, from the 

 form of the branch they are on, to make another position more central 

 to the available food, than to any instinct that makes them move at 

 any particular stage or instar. Different broods seem to vary a good 

 deal as to how far they remain gregarious in the last instar or become 

 quite solitary. If food remains at hand, few larvae wander far off 

 until they do so for pupation, but they cease to go to and fro so much, 

 and so, though still spinning silk to walk upon, do not increase the 

 considerable webs spun during the earlier "stages. Essentially, 

 perhaps, Vanessa io and Aglais urticae do the same as Euvanessa 

 antiopa and Eugo?iia polychloros, but the abundant web they spin in 

 their earliest instars is but slightly added to (comparatively) in the 

 intermediate stage, and, in the final instar, gregariousness seems to 

 have ceased. Aglais urticae has a habit very similar to that of 

 Pyrameis atalanta, of forming a leaf into a pocket. It brings the 

 opposite edges together of one leaf only, it never, so far as I have 

 observed, uses more than one, and, like P. atalanta, it eats the 

 terminal half of the leaf, destroying the domicile. The number of 

 caterpillars of A. urticae that make this tent is only a small proportion 

 of each brood, probably it is made for the safety of the larva during 

 the last moult, as they are always occupied by nearly full-grown 

 larvae." These remarks are highly suggestive that the maintenance of 

 the gregarious habit, and the continuance of the use of, and extension of, 

 and even moving of, the silken home of the tree-feeding species, are of 

 advantage to them, and there is no advantage so distinct that occurs 

 to one as the comparative security such a home offers during storms 

 of wind and rain, when willow-trees are badly bent, and the chance of 

 destruction to large larvae with no special means of retaining a firm 

 foothold, becomes very great indeed. Trouvelot's account (Proc. Bos. 

 Soc. Nat. Hist., xii., p. 92) of the way that the larva of Jasoniades 

 glaucus makes itself safe during rain-storms, has been repeatedly 

 quoted. He says : " Every one knows that the larva of this species, 

 when at rest, remains upon the middle of the upper part of a leaf ; for 

 this purpose a carpet of silk is spread upon the leaf by the larva. 

 This leaf, by means of the silk, is made to curve a little. On one 

 rainy morning, I observed a young larva of this species on a lilac bush 

 in my garden. I certainly thought that the invention of resting in 

 the hollow of a curved leaf on a rainy day was a very poor one, for, 

 since the bent leaf performed the office of a gutter, the water must 

 flow through this channel, and the larva be inundated and inevitably 

 drowned, if the rain lasted but a few hours. I soon found that there 

 were more brains in the small head than I had supposed. The larva 

 began to move ; it spun some silk from one edge of the leaf to the 

 other, and, by adding many fibres to make it strong, each new fibre 

 shorter than the preceding, the leaf was soon made to curve more and 

 more. I then began to understand what this laborious work was for, 

 and I thought that sometimes small people might give lessons to 

 larger ones. After about an hour, the larva ceased to work, a real 



