218 



FAMILY VI. — HYDRO PHILIDJE. 



implies, they are usually found in ponds and streams, but are less 

 active swimmers than the majority of the diving beetles. In swim- 

 ming- they move the hind legs alternately, while the Dytiscidae strike 

 with them both together, like a frog. Several genera are, however, 

 terrestrial in habit, living in moist earth and in the dung of cattle, 

 where they are said to feed upon the larvae of dipterous insects. 



The principal characters of the Hydrophilidae, briefly stated, 

 are as follows : eyes large ; mentum large, quadrate ; antennae with 

 from six to nine joints, the outer ones forming an abrupt club, of 

 which all the joints except the first are pubescent ; inserted under 

 the sides of the front behind the base of the mandibles. Thorax 

 with episterna and epimera not distinct, the prosternum very short, 

 Seutellum always present, Metasternum large, frequently carinate 

 and produced into a long spine behind. Hind coxa? oblique, flat, 

 extending to sides of abdomen, the latter with five visible segments. 

 Tarsi 5-jointed, the first joint often very small, the middle and hind 

 ones sometimes compressed and fringed for swimming. 



As their common name denotes, the water scavenger beetles are 

 supposed to live upon decomposing aquatic vegetation, but the 

 larvae are carnivorous and often catch and eat living insects and 

 water snails. These larva? resemble somewhat those of the diving 

 beetles, but the body is more plump and the mandibles shorter and 

 usually toothed. The eggs of the larger species are encased by the 

 female in a waterproof receptacle, formed of a silk-like secretion. 

 These egg-cases, which sometimes contain 100 or more eggs, are 

 either fastened on the under side of leaves of water plants, or are 

 allowed to float free. In a few instances the cases are carried about 

 by the mother on the under side of her body until the young hatch. 

 The pupal stage is undergone on land, in an underground cell or in 

 a cavity scooped out beneath some object close to the water's edge. 



The principal literature treating of the North American species 

 of the family is as follows : 



LeConte. — "Synopsis of the Hydrophilidae of the United 

 States," in Proc. Phil. Acad. Nat. Sci., VII, 1855, 356-375. 



Horn — "Revision of the Genera and Species of the Tribe Hy- 

 drobiini," in Proc. Amer. Phil. Soc, XIII, 1873, 118-137. 



Horn. — "Synoptic Tables of some Genera of Coleoptera, " in 

 Trans. Amer. Entom. Soc, V. 1876, 251. 



Horn. — "Notes on the Species of Oehthebius of Boreal Amer- 

 ica," in Trans. Am. Ent. Soc, XVII, 1890. 17-26. 



