AQUATIC INSECTS 



off the stone it hangs to its anchorage by a delicate silken 

 thread spun from its salivary glands; by this means too it can 

 travel downstream, swinging from rock to rock. Simtdiiim 

 larvae breathe by the three retractile blood-gills at the hind 

 end cf the body. 



The pupal cocoons form golden brown blankets on the 

 rocks even more moss-like than those of the larvae. They 

 breathe through tracheal gills, the fringes which wave from 

 the top of each case. Like all swift-water insects the adults 

 fly as soon as they emerge, laying their eggs shortly afterward 

 (Fig. 233). Black-fly larvae are eaten in large numbers by 

 fishes. Adult black-flies are pests both to human beings and 

 animals, and black-fly cream and other repellents are sold all 

 through the country where they abound. The Maine fisher- 

 men grease their hands and faces with kerosene oil and mutton 

 tallow. Black-flies are active only during the daytime, leav- 

 ing twilight to the mosquitoes and punkies. 



Net-veined midges, Family Blepharoceridae, larvae. — The 

 larvae of Blepharocera cling to the stones in the rapids of 

 mountain streams, in the waters of ravines, and in rushing 

 brooklets. In their own special haunts they are abundant 

 and no member of waterfall society is better equipped with 

 holdfasts. 



Clinging to its stone it looks like a row of six little black 

 beads, Jess than half an inch long, the first bead consisting of 

 the fused head and the thorax, the other five representing 

 the abdomen (Fig. 234, i). It has no feet, but down the mid- 

 ventral line is a row of six sucking disks which it uses in 

 walking and clinging (Fig. 234, 2). It breathes by means 

 of the tufted tracheal gills on each segment. 



Pupae. — The pupae are egg-shaped with a pair of ear-like gills 

 at the large anterior end (Fig. 234). 



Adults. — The adult females of some exotic tropical species 

 are blood-sucking but the majority, including our North Am- 

 erican forms, are not. Abundant in May. 



297 



