FIELD BOOK OF PONDS AND STREAMS 



body tipped up (Fig. 231). Anopheles eggs float singly on 

 the surface. When at rest Anopheles larvas always lie parallel 

 to the surface of the water, with the under side of the abdomen 

 upward so that their two short air-tubes opening from the 

 eighth segment can reach the air (Fig. 232). 



Black-fiies, Family Simuliidae. — Thousands of these lar\^ae 

 make up the swaying greenish "black moss" which covers 

 the rocks in waterfalls and rapid streams from Alay to mid- 

 summer, where hundreds can be gathered at a stroke of one's 

 hand. This family includes the Adirondack black-fly, Prosi- 

 miilium hirtipes, which is a scourge along the northeastern 

 mountain streams in spring and early summer. 



Fig. 233. — The black-fly SimuUiun: i, larva 

 which hangs to the rock by a caudal sucker and 

 collects food with its fan-shaped brushes; 2, pupa 

 showing tracheal gills; 3, adult. Length, larva, one 

 quarter inch. 



Simulium. — The larva holds fast to the rocks by a sucking 

 disk at the hind end of its body. This frees the mouth to 

 take in the diatoms gathered on the fan-shaped collecting 

 brushes (Fig. 233, i). The fleshy proleg just behind the head 

 ends in a sucker like the rear one and on these two the larva 

 walks over the stones. If it loses its footing or is brushed 



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