110 FLOATING FLIES 



eign building materials, and often a complete 

 inner silken lining is made. 



"The larvae within the cases are worm- or 

 caterpillar-like, with head and thorax usually 

 brown and horny-walled, while the rest of the 

 body is soft and whitish. The head with the 

 mouth-parts, and the thorax with the long 

 strong legs, are the only parts of the body that 

 project from the protecting case, and hence 

 need to be specially hardened. At the posterior 

 tip of the abdomen is a pair of strong hooks 

 pointing outward. These hooks can be fast- 

 ened into the sides of the case and thus hold 

 the larva safely in its house. . . . The 

 caddis worm crawls slowly about searching for 

 food, which consists of vegetable matter. 

 Those larvae which have fixed cases have to 

 leave it in search of food. Some of them make 

 occasional foraging expeditions to consider- 

 able distances from home. Others have the in- 

 teresting habit of spinning nearby a tiny net 

 fastened and stretched in such a way that its 

 broad shallow mouth is directed upstream, so 

 that the current may bring into it the small 

 aquatic creatures which serve these caddis-fish- 

 ermen as food. The caddis flies live several 

 months, and according to Howard some pass 

 the winter in the larval stage. 



