COLEOPTERA 



141 



The larvae vary greatly in form; some are campodeiform, some are 

 scarabeiform, and others are vermiform; in none are the legs more than 

 five-jointed, and in none are the legs two-clawed. 



This suborder includes all but the few preceding families of the 

 Coleoptera. 



Family Hydrophilid^ 



The Water-scavenger Beetles 



The water-scavenger beetles are common in quiet pools, where they 

 may be found swimming through the water, or crawling among the 

 plants growing on the bottom. They can be easily taken by sweeping 

 such plants with a dip-net. 



They are elongated, elliptical, black beetles, resembling the preda- 

 cious diving-beetles in appearance; but they are usually more convex, 

 and differ also in having club-shaped antennas and very long palpi. As 

 the antennae are usually concealed beneath the head, it often happens 

 that the inexperienced student mistakes the long palpi for antennae. 



These beetles are supposed to live chiefly upon the decaying vegeta- 

 tion in the water; but a number of species have been known to catch 

 and eat living insects. They breathe by carrying a film of air on the 

 lower surface of the body. This film gives them a silvery appearance 

 when seen from below. They obtain the air by bringing the head to 

 the surface of the water and projecting the antennae, which they again 

 fold back with a bubble of air when they descend. The female makes a 

 case for her eggs out of a hardened silk-like secretion. j^ 



Some species deposit as many as a hundred eggs in one of 

 these water-proof packages (Fig. 238). The egg-cases in 

 some instances are fastened beneath the leaves of aquatic 

 plants; in others they are provided with floats and let 

 loose in the water ; and in still other species the cases are 

 carried by the mother underneath her body and steadied 

 with her hind legs. Frequently some of the young larvae 

 devour their companions; in -this way the size of the fam- 

 ily is decreased before it escapes from 

 the egg-case. Later they live upon insects that fall 

 into the water, and upon snails. These larvae re- 

 semble somewhat those of the Dytiscidae; but the 

 body is much more plump, and the mandibles are 

 of moderate size. 



The family Hydrophilidae is represented in North 

 America by one hundred and ninety species. The 

 largest of our common species is Hydrous trian- 

 gularis (Fig. 239). In the genus Hydrous the met- 

 asternum is prolonged backward into a spine 

 between the hind legs, and the sternum of the protho- 

 rax bears a deep furrow. 



Next in size to Hydrous are several species of 

 Hydrophilus. In this genus the metasternum is 

 prolonged somewhat, but does not form a long, sharp spine as in Hydrous 

 and the sternum of the prothorax bears a keel-shaped projection. Our 



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Fig. 2,38. 



