THE TRICHOPTERA 



227 



made differ according to the species of Caddice-fly concerned and vary 

 greatly (Fig. 226). Some take pieces of leaves which have fallen into the 

 water; others select veins of the leaves and similar sized straws and put 

 them together cris-cross, something like the logs of a log house; some 

 species use the finest sand for this purpose; 

 others coarse gravel, and still others use a mix- 

 ture of long and short pieces of plants so that 

 the ends of the longer ones extend some distance 

 behind the end of the case. 



The case itself is usually straight but in some 

 species it may be curled, and resembles a small 

 snail-shell. Indeed this resemblance is so close 

 that in one instance at least, such a case was 

 actually described as that of a shell! The ma- 

 terials, whatever they may be, are held together 

 by silk spun by the larva, coming from silk glands 

 within the body and poured out through an 

 opening close to the mouth. Within the case 

 the larva lives, crawling about by extending its 



FIG. 224. Caddice-flies: adult at rest, above; with wings spread, below. Larvae showing 

 three kinds of cases, crawling. (From Linville and Kelly, General Zoology.) 



head and thorax out of the front end so that its feet can be used, and 

 dragging the case along. 



Some caddice-fly larvae make simpler houses than these. Such species 

 live in rapid water and there fasten a few tiny stones under rocks by their 



