AQUATIC INSECTS 



cuts its canopy away, leaving only a clean scar on the rock 

 surface. Within the area of this scar it makes its pupal case. 

 This has an inner case of loose-spun silk wliich encloses the 

 pupa with radiating threads which suspend it from a canopy 

 thicker than the larval one but perforated with a circle of 

 six or more clean-cut holes which let in the water. 



The moths (Fig. 202, 3) emerge in Jun? and July and the 

 vegetation near the stream sometimes swarms with them. 

 Their front wings are gray-brown and their hind wings white 

 marked with a curved blackish band. Common and general 

 in distribution. 



Beetles — Coleoptera 



When they are fuUgrown nearly all beetles have thick 

 wing-covers or elytra which hide the thin hind wings beneath 

 them. They change greatly in form from larva to pupa to 

 adult (Fig. 203) and the young in no way resemble the mature 

 beetles. As a group beetles are preeminently land insects. 

 Of the 150,000 or so species of Coleoptera included in approxi- 

 mately eighty families only a few families are made up of 

 water-loving beetles. 



Fig. 203. — The change of form in a water-beetle; 

 I, larva; 2, pupa (after Wilson); 3, adult. 



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