| Fig. 472.—Bristles at the extremity of the abdomen of the Hydrophilus. | Fig. 473.—Pupa of the Hydrophilus. |
We are now going to consider a series of aquatic and carnivorous insects; the Dytisci, Water Beetles, the Cybisters, and the Gyrinidæ, or Whirligig Beetles. These are perfect corsairs, whose rapacity even exceeds that of many of the land Coleoptera. Not contented with devouring one another, when pressed by hunger, with attacking especially the larvæ of all aquatic insects, such as the Libellulæ and Ephemeræ, they feed also on molluscs, on tadpoles, and on small fish. It is easy to rear them in captivity. If confined in a small aquarium, their habits would be much more amusing than a few golden fish, which one meets with everywhere, and which are only good enough to amuse European Schaabahams. Care must be taken to cover the aquarium at the top with gauze, to prevent the perfect insects from escaping. This tribe is not very numerous nor varied in its forms. An oval body, legs curved and widened into oars, provided with hairs, distinguish the insects which compose it. They imbibe air at the surface of the water.
Fig. 474.—Dytiscus marginalis, male and female, and front leg of male magnified.
The most carnivorous of this group are the Dytisci and the Cybisters. They may be called the sharks of the insect world. Nothing which lives in the water is safe against the voracity of the Dytiscus. They attack small molluscs, young fish, tadpoles, larvæ of insects, and suck greedily the bits of raw meat which are thrown to them. They may be kept in an aquarium for many years by feeding them on animal matter. Their oval-shaped body, with its sharp sides, permits them to cut through the water with great ease—the hind legs serving as oars. They are to be found in stagnant waters during the greatest part of the year, but principally in autumn. During the winter they bury themselves in the mud and under moss. The females lay their eggs in the water. The larvæ are long, swelling out at the middle, furnished with hairs, and grow rapidly. To undergo their metamorphosis into pupæ they bury themselves in the earth.
Fig. 475.—Pupa and larva of Dytiscus marginalis.
| Fig. 476.—Dytiscus latissimus. | Fig. 477.—Cybister Rœselii. |