TROUT STREAM INSECTS 109 



of the group being almost restricted to the 

 aquatic larvae, whose cleverly built protecting 

 cases or houses made of sand, pebbles, or bits 

 of wood held together with silken threads give 

 the insects their common name, i. e., case or 

 caddis worms. 



" The cases are familiar objects in most 

 clear streams and ponds. There is great 

 variety in the materials used and in the size and 

 shape of the cases, each kind of caddis worm 

 having a particular and constant style of house- 

 building. Grains of sand may be fastened to- 

 gether to form tiny, smooth-walled, symme- 

 trical cornucopias, or small stones to form 

 larger, rough-walled, irregular cylinders. 

 Small bits of twigs or pine needles may be 

 used; and these chips may be laid longitudinally 

 or transversely and with projecting ends. 

 Small snail-shells or bits of leaves and grass 

 may serve for building materials. 

 While most of the cases are free and are car- 

 ried about by the worm in its ramblings, some 

 are fastened to the boulders or rock banks or 

 bed of the stream. These fixed cases are 

 usually composed of bits of stone or smooth 

 pebbles irregularly tied together with silken 

 threads. In all the cases silk spun by the caddis 

 worm is used to tie or cement together the for- 



