TRICHOPTERA 79 



They serve for catching food which the current sweeps into 

 them. The larva lies protected within its shelter with its 

 head conveniently near to the bottom inside of the catching 

 net. Here at the bottom is a catching surface of much 

 finer mesh — a sort of woven dinner plate. 



In any riffle of a clear brook one may find these nets. 

 They are usually dirty from accumulated silt. They are 

 often somewhat funnel-like as seen from above. When made 

 by full grown larva they are about big enough to hold the tip 

 of one's thumb. They hang on the face of the stones or stems, 

 where the water may fall or glide into them. They are to be 

 found only in flowing water. 



Larvae may be easily obtained by taking them from their 

 shelters with a forceps or with a knife blade. 



When we examine a larva we find it has a rather soft, 

 thin-skinned, cylindric body with a hard horny head (this 

 part being often exposed from under the shelter) and with 

 a pair of large draghooks at its rear end. 



It has typical biting mouthparts, but with reduced palpi. 

 It has gills in dense tufts of clustered filaments underneath 

 the abdomen. Its rather strong legs are directed forward 

 for easy extension beyond the tubular shelter, and the front 

 tibia bears a rather distinctive spine. The paired draghooks 

 on the last segment of the body serve as an anchor to rear- 

 ward, holding firmly in the walls of the shelter tube. When 

 the larva has completed its growth, it builds a more sub- 

 stantial shelter of pebbles^or bits of wood and transforms 

 within it to a pupa of the form shown in figure 29. One may 



