l82 



THE STUDY OF INSECTS 



Perhaps the most remarkable species are the net-spinning caddice- 

 worms. The best-known of these are species of the genus Hydropsyche, 

 the nets of which have been described by many writers. 



Fig. 32a. — Case of Gtrra 

 calcarala. (After Lloyd.) 



Fig. 321. — Case 

 of H elico psyche. 

 (From Lloyd.) 



Fig. 322. — Net of Hydropsyche. 



The larvae of Hydropsyche live only in rapid streams and on the wave- 

 beaten shores of lakes. They do not build portable cases, but live in 

 tubes composed of silk and debris, and fastened permanently in place; 

 sometimes they establish themselves in old worm-holes in submerged 

 wood. The most striking feature in their habits, however, is the fact 

 that each one builds a net for the capture of its food. This net is built 

 adjacent to the tube in which the larva lives; it is funnel-shaped and has 

 at its down-stream end an opening in which is built a strainer. This is a 

 beautiful object, consisting of two sets of regularly spaced strands of 

 silk extending across the opening at right angles to each other (Fig. 322). 

 These nets are often built in crevices between stones; but fully as often 

 they are built up from a flat surface, as on the brink of a waterfall. 

 Much of the coating of dirt with which rocks in such places are clothed in 

 summer is due to its being caught in these nets. Algae, larvae, and other 

 small animals in the water that passes through the net are held by the 

 strainer and thus made available to the caddice-worm for food. 



