HOW TO KNOW THE IMMATURE INSECTS 



3a. Tip of abdomen with a caudal filament; sides of body with 7 pairs 

 of segmented filaments; without anal prologs. 

 Fig. 388 Family SIALIDAE 



The larvae live in swiftly flowing streams adher- 

 ing to the lower side of stones and also in trashy 

 places filled with aquatic plants. The full-grown lar- 

 va leaves the water and transforms in an earthen 

 cell on the bonks of the streams or lakes. Two or 

 three weeks later the adult emerges. It is called an 

 alderfly. The larvae are predacious and feed upon 

 different kinds of small animals. 



Fig. 388. Smoky 



alderfly, Sialis 



infumoto New- 

 man. 



3b. Tip of abdomen without a caudal filament; sides of body with 8 

 pairs of unsegmented filaments; with a pair of hooked anal pro- 

 legs. Fig. 389 Subfamily Corydalinae, SIALIDAE 



. PILAMENJ 



Fig. 389. Corydolus cornutus 



larva; b, pupa. 



( L. ) : a. 



About 80 species of dobson- 

 flies have been described. The 

 larvae are found under stones 

 in slow or swift water and are 

 predacious on naiads of dragon- 

 flies, stoneflies and Mayflies. 

 These larvae which are known 

 as helgramites are much used 

 for bait in fishing. They are 

 rather readily caught by hold- 

 ing a |iet down stream below 

 stones in rapids. When the 

 stones are moved the helgra- 

 mites swim or are washed into 

 the net. 



141 



