Caddis-worms 



217 



and into them the current washes organisms suitable 

 for food. The caddis-worm lies with ready jaws in wait 

 at the bottom of the funnel, and cheerfully takes what 

 heaven bestows, seizing any bit of food that may chance 

 to fall into its net. These net-spinners belong to the 

 family Hy dropsy chidae. 

 When minute animals 

 abound in the current the 

 caddis-worms appear to 

 eat them by preference: 

 at other times, they eat 

 diatoms and other algae 

 and plant fragments. 

 The order as a whole tends 

 to be herbivorous and 

 many members of it are 

 strictly so; but most of 

 them will at least vary 

 their diet with small may- 

 fly and midge larvae and 

 entomostracans, when 

 these are to be had. 



Caddis -worms are more or less caterpillar-like, but 

 lack paired fleshy prolegs beneath the body, save for a 

 single strongly-hooked pair at the posterior end. The 

 thoracic legs are longer and stronger and better devel- 

 oped than in caterpillars, and they are closely applicable 

 to the sides of the body, as befits slipping in and out 

 of their cases. The front third of the body is strongly 

 chitinized and often brightly pigmented; the 

 remainder, that is constantly covered by the case, is 

 thin skinned and pale. Most caddis-worms bear fila- 

 mentous gills along the sides of the abdomen, but some 

 that dwell in streams are gill-less and others have gills 

 in great compound clusters or tufts. 



Fig. 125. The larva of Rhyacophila 

 fuscula in its barricade of stones, 

 exposed by lifting off a large top 

 stone. 



