338 



Aquatic Societies 



Here belong the hosts of minute spring-tails that gather 

 in the edges in sheltered places, often in such numbers 

 as to blacken the surface as with deposits of soot. 

 Minute as these are they are readily recognized by 

 their habits of making relatively enormous leaps from 

 place to place. 



,^(2). Those that lie prone upon the surface. Best 

 known of these because everywhere conspicuous on still 



FIG. 198. Two fallen stems enveloped with a rich growth 

 of the alga, Chcetophora incrassata. 



waters, are the whirl-i-gig beetles. Less common and 

 irm.ch less conspicuous are the pupae of the soldier- flies 

 (Stratiomyia, etc.) and the larvae of the Dixa midges. 



(3). Those that hang as if suspended at the surface, 

 with only that part of the body that has to do with 

 intake of air breaking through the surface film. Here 

 belong by far the larger number of aquatic insects. 

 Here are the bugs and the adult beetles, alertly poised, 



