898 



FRESH-WATER BIOLOGY 



The orl flies (Sialis) are still smaller having an expanse of wing of 

 an inch or less. They are plain, blackish in color, and rather 

 secretive in habits. Sometimes they occur in such 

 numbers as to blacken the herbage about the pond 

 border. The larvae (Fig. 1367) live among the stones 

 and gravel in the bed of brooks, and in the borders 

 of ponds, and transform in the wet sand on shore. 

 They are readily distinguished from other larvae 

 by the long tail-like prolongation of the last seg- 

 ment of the body. The female lays her eggs (Fig. 

 1368) in broad, single layered, blackish patches on 

 some stick or timber above the surface of the 

 water. The lateral filaments of the abdomen in 

 Sialis are thin-skinned, and contain tracheae, and it 

 is possible that they serve as organs of respiration; 

 there are no additional clusters 

 of fine gills at their bases. Un- 

 like the foregoing, these larvae 

 descend into the bottom silt 

 and burrow through it, and their long ab- 

 dominal filaments are close laid on the back, 

 as are the gills of the burrowing Mayfly 

 nymphs. 



There is a striking general similarity be- 

 tween the larvae of the Sialididae and those 

 of the more generaHzed carnivorous Coleoptera. 



Hemerobiidae. Only two genera in this large family of attrac- 

 tive insects are aquatic in our fauna, Climacia and Sisyra (Fig. 1369). 

 These are small insects, half an inch or less in expanse of wing, 



Fig. 1367. The larva 

 of the orl fly, Sialis 

 infumata. 



Fig. 1368. The eggs of the 

 orl fly; from a photograph. 



Fig. 1369. A spongilla fly, Sisyra. 



the former yellow and brown in color, the latter, plain brown. 

 Nothing is known of the feeding habits of the adults. Their larvae 



