SURROUNDINGS OF GROWING INSECTS 231 



viridana), which rolls the terminal part of an oak-leaf trans- 

 versely into a neat cylinder, and by a saw-fly (Blennocampa 

 pusilla), which rolls rose-leaflets closely and longitudinally. 

 The Erastria caterpillar, just mentioned, illustrates the habit 

 of forming a portable case, a more familiar instance of which is 

 afforded by the common clothes-moth (Tinea) caterpillars. 

 These spin together the pellets of their own excrement with 

 their silk, and thus build tubular cases which they carry about 

 with them, as they nibble at the woollen fibres of garments 

 or the fur of skins. The tubes formed by midge grubs in 

 ponds and ditches have already been mentioned in this chapter, 

 and among aquatic larvae no group offers more perfect demon- 

 stration of the case-building habit than the caddises 

 (Trichoptera, see pp. 122, 141). Caddis-larvae of different 

 families make houses of various objects -fragments of 

 water plants, small stones, snail-shells ; and the caddis- 

 house may be portable (Phryganea) or fastened to a 

 submerged boulder as are the habitations of the 

 Hydropsychids, beautifully constructed of tiny stones. 



These shelters are all made of foreign objects which the larva 

 finds ready to hand, but the objects are fastened together 

 by silk, the creature's own secretion. Many young insects 

 protect themselves entirely with the products of their own 

 bodies. We have seen already (p. 193) the importance to the 

 Simulium grub of its silken labyrinth as an anchorage in the 

 swift streams that it inhabits, and the web-nest spun by the 

 united labour of the small ermine (Hyponomeuta) caterpillars 

 (p. 204) . Similar silken webs in which the members of a family 

 live as a loosely united community are spun by the caterpillars 

 of the Peacock butterfly (Vanessa io) on nettles, and by those 

 of the Lackey moth (Clisiocampa neustna] on various trees. 

 The hairy larvae of the Brown-tail moth (Euproctis chyysorrhaea) 

 are hatched from the eggs in autumn. They construct a 

 silken web-nest in which they pass the winter, resting and 

 taking no food, but the stimulus of spring sunshine incites them 

 to leave this warm shelter and climb up the shoots and twigs 

 of their food-plant in search of provender after the winter's 

 fast. Many of these web-spinning caterpillars are protected 

 in another way : by an abundant growth of hairs and spines 

 from the cuticle of the body, so that the soft wormlike larva 



