DYTISCUS, (Encycl.) The larvae of the dytiscus, water-beetle, or diver, are often met with in water. They are oblong, and have six scaly feet. Their body consists of eleven segments. The head is large, with
four filiform antennæ and a strong pair of jaws. The last segments of their body have rows of hairs on the sides; and the abdomen is terminated by two spines charged with the like hairs, forming a kind of plumes. These larvae are frequently of a greenish variegated brown: they are lively, active, and extremely voracious: they devour and feed upon other water-insects, and often tear and destroy each other. The perfect insect is little inferior to its larvae in voraciousness, but it can only exercise its cruelty on the larvae; the perfect insects, like himself, being sheltered by the kind of scaly cuirass with which they are armed. This creature must be touched cautiously; for besides its power of giving a severe gripe with its jaws, it has moreover, under the thorax, another weapon, a long sharp spine, which it will drive into one's fingers by the effort it makes to move backwards. The eggs of the dytiscus are rather large, and are by them inclosed in a kind of silky dusky cod, of a strong and thick texture, in form round, and terminated by a long appendix, or slender tail, of the same substance. These cods are often found in the water, and from them are brought forth the eggs and larvae of the dytiscus. The strength of these cods probably serves the insect to defend their eggs from the voraciousness of several other aquatic insects, and even from that of their fellow-dytiscus, who would not spare them.
Many species of the perfect insect are common in stagnated waters, which they quit in the evening to fly about. They swim with incredible agility, making use of their hinder-legs after the fashion of oars. The elytra of the females are in general furrowed, and those of the male plain: when they first arrive at their perfect state, their elytra are almost transparent, and in many species of a beautiful dun colour, mingled with shades of greenish brown. The best method of catching them is with a hand-net or sieve; for they are so nimble, and exercise their defensive weapons so often, and with such painful success, to those who endeavour to catch them, that they are very often obliged to let them escape; the easiest way to kill them, is to let them fall into boiling hot water, which instantly destroys them.