AQUATIC INSECTS IN THE ADIRONDACKS 54I 



cc Wiogs with many veins and liot covered with whitish powder 



d >Viug veins all terminating at the distal border of the wing in a suc- 

 cession of symmetric forks, the ultimate forks often forming a 

 peripheral zone around the distal margin of the wing 

 e Cross veins between the radius and its sector numerous (ten or more) 

 (Green or yellowish insects : lace wing flies ; larvae, aphis lions, 

 arboreal ; pupating in cocoon of silk, attached to the plants on 



which they have lived) Chrysopidae 



ee Cross veins between the radius and its sector few (two to six) 



Hemerobiidae 



dd Wing veins meeting the outer wing margin in straight lines. Forks 



fewer, more remote from the margin and less symmetric .. Sialidae 



The two families which contain our aquatic species will now be con- 

 sidered in detail. Their larvae have. already been distinguished in the 

 key to the orders of aquatic insect larvae. 



Family sialidae 

 Alder flies ^ fish flies, dob sons, etc. 



This family comprises but few genera and species ; but the large size 

 and the enormous number of individuals of some of the species make 

 them a well known part of the aquatic population. Few insects of incon- 

 spicuous coloration and secretive habits are so well known. Every 

 species, in larval as well as adult stages, is attractive food for fishes, and 

 many of them are among the insects most highly prized and most com- 

 monly used for bait. 



The adult insects do not wander far from the borders of their native 

 streams or ponds; they are generally found sitting closely on some 

 support, with wings folded like a roof over the back. They fly but little. 



The larvae are somewhat cylindric, with large heads and very large 

 raptorial mandibles, and -have on the sides of each of the first seven or 

 eight abdominal segments a pair of long, conspicuous lateral filaments. 



The eggs are deposited on any convenient support near the water, in 

 clusters whose form varies with the genus, and to a less extent, with the 

 species. 



Our three genera may be distinguished as follows. 



KEY TO GENERA OF SIALIDAE 



I??iagos 



a Fourth segment of the tarsus bilobed ; posterior branch of the radial sector 



forked. No ocelli Sialis 



aa Fourth segment of the tarsus simple, cylindric ; posterior branch of the 

 radial sector simple. Three ocelli 



