THE PREDACE0U3 DIVING BEETLES. 



205 



ward being derived from the .Greek Dytiscus, meaning a diver. All 

 the species are more or less aquatic in habit and, as a rule, are 

 strong swimmers. Many of them hibernate as imagoes, burrowing 

 in the banks and mud at the bottom or sides of the pools in which 

 they dwell. Dr. Harris kept one for "three years and a half in 

 perfect health, in a glass vessel filled with water, and supported by 

 .morsels of raw meat. It was capable of fasting a month; was very 

 sensible to the changes of the weather, which it indicated by the 

 height at which it remained in the vessel." They are often seen 

 beneath the ice in late autumn or early spring. In the mature 

 stage, during the mating season, some of the larger species fly about 

 at night and are often attracted in numbers by electric and other 

 lights. 



From the Haliplidas they may be readily known by having the 

 body less stout and convex and more obtuse at the ends; antennae 

 glabrous, ll-jointed. usually filiform, and inserted under the front 

 behind the base of the mandibles; middle and hind pairs of legs 

 widely separated, due to the very large hind coxae, which reach 

 the sides of the body but do not cover the ventral segments. The 

 hind legs are the longest, and are strongly adapted for swimming, 

 being flattened and fringed with long hairs. The spiracles open 

 beneath the elytra on the upper surface of the abdomen. By lift- 

 ing the elytra slightly an air chamber is formed, from which the 

 beetle draws its supply while, swimming. When the air in this 

 chamber becomes too impure, the insect rises to the surface, forces 

 it out and renews the supply. In color the beetles are usually 

 brownish-black, often with a dull glaucous or sea-green tint, very 

 smooth and shining. Some of them have the thorax and margins of 

 elytra marked with dull yellow. 



The sexes of several of the genera possess modifications which 

 are of especial interest and which furnish excellent characters for 

 the separation of groups. In the males of these genera the three 

 basal segments of the fore (and sometimes the middle) tarsi are 

 dilated and form a circular disk on the under side of which are 

 numerous small, cup-like suckers. These serve as 

 clasping organs. (Fig. 104.) The females of cer- 

 tain species also present an interesting dimorphism, 

 in that some of them have the elytra deeply fur- 

 rowed, while others of the same species have them 

 smooth. 



The Dytiscida? are among the most voracious of (After* ComSock.) 

 all beetles. They prey not only upon the larvae of 



