FIELD BOOK OF INSECTS. 



water support, the ends are covered with a loose silk 

 netting and the change occurs in the privacy of the larval 

 home. Polycentropus lucidus builds a stationary, tunnel- 

 like dwelling in the silt where the current is slight and 

 species of Hydropsyclie build stone ones, which are anchored 

 to larger stones in places where the current is swift. 

 With the possible exception of Hydropsyclie, caddice- 

 worms seem to be vegetarians. Hydropsyclie may be 

 carnivorous and Hydropsyclie analis has long been an 

 object of interest with those who know. Its larva lives 

 in the very swiftest of streams in a rather rude, but firmly 

 fastened, hut of pebbles and debris; not far from its door 

 it makes a net (see Plate XV) between small stones or on 

 the top of some large stone where it is in the current's 

 sweep. This net is always placed across stream and its 

 top is often framed with sticks. Now all H. analis needs 

 do, when hungry, is to go out of its hut and eat whatever 

 food the net has caught. On such excursions it keeps 

 hold of a strand of silk which has one end fastened to the 

 door so that it can pull itself back if the current should 

 loosen its footing. Pupation takes place in the larval 

 dwelling, but how about the adult? Most insects slowly 

 work their way out of the pupal case and then rest for 

 some time until their wings are dry and strong. This 

 would never do for H. analis, nor for many other species of 

 Trichoptera, since fish would snap them up even if the cur- 

 rent did not overpower them. It is said that the pupa leaves 

 its protective case, swims to the surface, and instantly the 

 adult shoots out of the pupal skin and flies away. 



The classification of adult caddice-flies is not easy and, 

 as the chief interest is in the larva?, the following key, 

 based on larval characters, is given. It is a modification 

 of one in Bulletin 4 7 of the N. Y. State Museum and 

 includes the principal families. 



I. Head bent downward at an angle with the body: 

 tubercles usually present on the basal abdominal segment; 

 gill filament, when present, simple (except in some Limno- 



philidae), lateral fringe usually present 2 - 



Head in line with the main axis of the body; tubercles 

 and lateral fringe absent; gill filaments, when present, 



branched > 



58 



