AQUATIC INSECTS 897 



DoBSONS, Fish Flies, Spongilla Flies {Order Neuroptera) 



But two families of this great and heterogeneous order, as now 

 commonly restricted, are aquatic, and these in their larval stages 

 only. The larvae of all the members of the small family Sialididae 

 are free-ranging carnivorous, aquatic forms, and in the family 

 Hemerobiidae, there are a few genera whose larvae hve in the 

 water. These two families are so very different in every respect 

 that they are better considered separately. 



Sialididae. Here belong a few of the most primitive of insects 

 having complete metamorphosis: the orl flies, fish flies, dobsons, 

 etc. They are mostly of large size, and are provided with ample 

 wings, which, however, serve but rather poorly for flight. The 

 dobsons are among the largest of insects, and their larvae, known 

 to the fishermen as hellgrammites, are famous as bait for black bass. 



They are found in swift streams beneath the stones, where they 

 cling securely by means of their stout legs, aided by a pair of stout- 

 clawed processes at the end of the body. They are 'provided at 

 the sides of the abdomen with paired lateral fleshy processes, and 

 at the base of each of these there is a large tuft of fine tracheal gills. 

 They are blackish, ugly-looking crawlers, of slow growth, requiring 

 apparently several years to develop. When grown they crawl 

 out on shore and seek a suitable place beneath a log or stone; 

 for the pupae are not aquatic. The adult female lays her eggs in 

 broad flat masses on stones or timbers above the edge of the water, 

 and covers them over with a chalky white incrustation. The 

 eggs are piled several layers deep and are very numerous. On 

 hatching the young fall into the water, and begin at once their 

 predatory existence. But one species of dobson is found in the 

 eastern United States, the common Corydalis cornuta L. The 

 fish flies (Chauliodes) are insects of similar appearance and 

 habits, about half as large as the dobsons, having an expanse 

 of wing of about one and a half inches. Their larvae usually fre- 

 quent still water, where they clamber over and under logs. A 

 rotten log on shore furnishes the favorite place for the excavation 

 of a pupal chamber. The eggs are laid above the water in naked 

 patches of one or more layers on either dead wood or green leaves. 



