Certain Coleoptera are known to prey upon Helices and other land Mollusca. Récluz noticed, near Agde, a beetle (_Staphylinus olens_) attack _Helix ericetorum_ when crawling among herbage, sticking its sharp mandibles into its head. Every time the snail retreated into its shell the beetle waited patiently for its reappearance, until at last the snail succumbed to the repeated assaults. M. Lucas noticed, at Oran, the larva of a _Drilus_ attacking a _Cyclostoma_. The _Drilus_ stood sentinel at the mouth of a shell, which was closed by the operculum, until the animal began to issue forth. The _Drilus_ then with its mandibles cut the muscle which attaches the operculum to the foot, disabling it sufficiently to prevent its being securely closed, upon which it entered and took possession of the body of its defenceless host, completing its metamorphosis inside the shell, after a period of six weeks.[137] The female glow-worm (_Lampyris noctiluca_) attacks and kills _Helix nemoralis_. Among the Clavicornia, some species of _Silpha_ carry on a determined warfare against small Helices. They seize the shell in their mandibles, and then, throwing their head backwards, break the shell by striking it against their prothorax. The common water beetle, _Dytiscus marginalis_, from its strength and savage disposition, is a dangerous enemy to fresh-water Mollusca. One _Dytiscus_, kept in an aquarium, has been noticed to kill and devour seven _Limnaea stagnalis_ in the course of one afternoon. The beetles also eat _L. peregra_, but apparently prefer _stagnalis_, for when equal quantities of both species were placed within their reach, they fixed on the latter species first.[138] In East Africa a species of Ichneumon (_Herpestes fasciatus_) devours snails, lifting them up in its forepaws and dashing them down upon some hard substance.[139] In certain islands off the south coasts of Burmah, flat rocks covered with oysters are laid bare at low tide. A species of Monkey (_Macacus cynomolgus_) has been noticed to furnish himself with a stone, and knock the oysters open, always breaking the hinge-end first, and then pulling out the mollusc with his fingers.[140] The walrus is said to support himself almost entirely on two species of _Mya_ (_truncata_ and _arenaria_), digging them out of the sand, in which they live buried at a depth of about 1½ feet, with his powerful tusks. Whales swallow enormous numbers of pelagic molluscs (_Clio_, _Limacina_), which are at times so abundant in the Arctic seas, as to colour the surface for miles. Many of the larger Cetacea subsist in great part on Cephalopoda; as many as 18 lbs. of beaks of Teuthidae have been taken from the stomach of a single _Hyperoodon_.