Nerve-winged Insects; Scorpion-flies; Caddis-flies 241 



laid longitudinally or transversely and with projecting ends. Small snail- 



shells or bits of leaves and grass may serve for building materials. One kind 



of caddis- worm makes a small, coiled case which so much resembles a snail- 



shell that it has actually been described as a shell by conchologists. Some 



cases in California streams gleam and sparkle in the water like gold; bits 



of mica and iron pyrites were mixed with other bits of mineral picked up 



from the stream - bed to form 



these brilliant houses. An Eng- 



lish student removed a caddis- 



worm from its case, and pro- 



vided it only with small pieces 



of clear mica, hoping it would 



build a case of transparent walls. 



This it really did, and inside its 



glass house the behavior of the 



caddis -worm at home was ob- 



served. While most of the cases 



are free and are carried about by 



the worm in its ramblings, some FIG. 331. FIG. 3320. FIG. 3326. 



are fastened to the boulders or FIG. 331. Two cases of caddis-worms. (Natu- 



rock banks or bed of the stream. 



cases of caddis-worms with the 

 These fixed cases are usually com- larval insects within showing head and thorax 

 posed of bits of stone or smooth P r J ectin g- (Natural size.) 

 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 foreign build- 

 ing materials, and often a complete inner silken lining is made. 



FIG. 333. Halesus indistinctus. (After Needham; enlarged.) 



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 



