HYDROPHILUS, in natural history, a genus of insects of the order Coleoptera. Antenna clavate, the club perfoliate ; feelers four, filiform ; the hind legs are formed for s*imming, fringed on the in ner side, and nearly unarmed with claws. The insects of this genus, like those of the which see, are inhabitants of ponds and stagnant waters, where they swim with much dexterity, turning round with great velocity ; they fly abroad by night in search of other waters. The males are distinguished from the females, by having a horny concave flap or shield on the fore legs, near the setting on of the feet ; the hind legs are peculiarly fitted for their aquatic situation, being furnish ed on the inner side with a series of long and close-set filaments, resembling a fin, by which they are enabled to swim with great ease. The larva remain about two years and a half before they change into pupa, forming a convenient cell, and se creting themselves in some bank. They
are very voracious, and destructive to the more tender aquatic insects, worms, and young fish, which they seize with their forked jaws, and destroy, by sucking- out their juice. There are upwards of thirty species. The principal European species is the H. piceus, water-clock. The fe male of this species affords an example of a faculty, which seems to be exercised by no other insect of this order, viz. that of spinning a kind of web, or flattish circu lar case of silk, which it leaves floating on the water, and in which it deposits its eggs. This case, says Dr. Shaw, is termi nated, on its upper surface, by a length. ened conical process, resembling a horn, of a brown colour, and of a much stronger nature than the case itself, which is white. The larva, as soon as hatched, make theft escape from the envelopement of the case, and commit themselves to the wa ter.