TRICHOPTERA 



563 



the net is built up from a horizontal surface its sides are supported by 

 bits of wood. Algae, larvee, and other small animals in the water that 

 passes through the net are held by the strainer and thus made avail- 

 able to the caddice-worm for food. When the larva is full-grown it 

 surrounds itself with a case composed of fine sand or gravel in which 

 to transform; this case is firmly cemented in place, and, in some 

 species at least, is closed at each end with a silken grating. The 

 instantaneous flight of the newly emerged adult when it reaches the 

 surface of the water has been referred to on an earlier page. 



Family PHILOPOTAMID^ 



The larv£e of members of this family are campodeiform and live in 

 rapid streams. Several of them were studied by Miss Alice A. Noyes, 

 but as yet an account of only one of 

 them, Chimdrrha aterrima, has been 

 published (Noyes '14). This larva 

 spins a delicate silken net resem- 

 bling in shape the finger of a glove. 

 The average size of the net of a 

 growing larva is about 25 mm. long 

 and 3 mm. wide. The nets are rarely 

 found singly, but are generally 

 placed five or six in a row (Fig. 693) ; 

 sometimes they occur in great num- 

 bers, completely covering the stones 

 with a thin, flocculent mass of dirty 

 silk. There is a large opening at 

 the end of the net facing the current, 

 and a smaller opening at the hind 

 end. The nets are fastened in place 

 at the entrance; the rest of the sac 



floats freely, and is kept distended by the current. The net serves 

 both as a hiding-place for the larva and as a sieve through which the 

 flowing water is strained; the larva feeding on the organic particles 

 that are entangled in it. The full-grown larva covers itself with an 

 inegular dome of pebbles in which to transform, and spins about its 

 body a delicate cocoon. 



Fig. 693. — Nets of Chimarrha aterri- 

 ma, natural size. (From Noyes.) 



Family POLYCENTROPID^ 



The larvaj are campodeiform ; they usually live in flowing water, 

 but some are found in standing water. They do not build portable 

 cases, but make fixed silken tubes or nets. The nets of several 

 European genera have been described; for an abstract of these 

 accounts, see Noyes ('14). The nets of American species have been 

 described by Clark ('91), Vorhies ('09), Noyes ('14), and Lloyd ('21). 



