AQUATIC INSECTS 



Some caddis flies, like the HydropsychidcB, lay their eggs in 

 beautifully regular layers upon submerged sticks, and the 

 hundreds of little embryos can be seen through the trans- 

 parent shells. The eggs of some of the Phryganida are 

 embedded in rings of gelatine, hung on aquatic plants. 



Habitat and season. — For every kind of aquatic situation 

 there is a caddis fly population, net-builders (PI. XVI) in the 

 rapids, clamberers and floating case-bearers in the gentle 

 currents. Different species of caddis flies have very definite 

 seasons when they emerge from the water as adults, and in 

 many kinds these are brief periods. But some can be found 

 all through the summer and a few, especially the net-builders, 

 HydropsychidcB (PL I, 6), can be found all winter. 



Microcaddis files, Family Hydroptilidae. — The larvae are all 

 less than one-quarter of an inch long; abdomen wider than 

 thorax; their cases (Fig. 189J shaped like spectacle cases and 

 generally carried edge upward. 



Fig. 189. — Larva and case of Ithytrichia confusa, 

 a microcaddis worm. (After Lloyd.) -^ 



Ithytrichia confusa. — The case of at least one species, Ithy- 

 trichia confusa (Fig. 189), is fastened limpet-like to the stone. 

 This is an oval parchment-like one, about a quarter of an 

 inch long, with an opening at one end through which the larva 

 feeds. They are common both in quiet water and flowing 

 streams. 



Family Rhyacophilidae. — This family is divided into two sub- 

 families but the larvae of both live in rapidly flowing streams. 



249 



