Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/154

Rh 130 COLEOPTERA in subterranean caves, and are both colourless and blind ; while such forms as Blennis areolatus, found on the coast of Normandy, live for the most part under water, being only found when the tide is low. II. Hydradephaga, or Carnivorous Water Beetles, are oval and somewhat depressed in form, with the two posterior pairs of legs flattened and otherwise fitted for swimming. They include the Diving Beetles (Dytiscus) and the Whirligigs (Gyrinus). The former (Plate VII. figs. 3-7) occur in all quarters of the globe, and are truly amphibious, for although water is their favourite element, they survive for a long time on moist land, and most of them fly about in the evening and morning twilight with great power and speed. When needing to breathe they allow themselves to float on the surface of the water, raise their elytra, and expose their stigmata to the atmosphere, thus getting quit of exhausted air and obtaining a fresh supply, which is stored up by closing the elytra. They are exceedingly voracious, devouring aquatic insects, as Hydrophilus piceiis, much larger than themselves, and doing considerable damage in fish ponds by devouring the young fish. They are readily kept in confinement, having been known to live thus for 3|- years, feeding on raw beef and insects. The larvae are even more voracious than the perfect insects, sucking the juices of their prey through perforated mandibles, and protected from attack by their horny integuments. Whirligigs (Gyrinus] (Plate VII. figs. 10, 11) differ from the Diving Beetles in the antennae, which are short and stout, and are so placed as somewhat to resemble ears. They are sociable creatures, and may be seen in ponds and ditches, congregated in groups varying from 2 to 100, swimming upon the surface with their backs above the water, and chasing each other in circles or darting about in more irregular gyrations. Unlike other water beetles their backs show a brilliant metallic lustre, and when darting about in the sunshine they look like pearls dancing on the surface. Their eyes are so divided as to appear to consist of two turned upwards and another pair looking downwards. The larvae (Plate VII. fig. 1 7) are long, slender creatures somewhat resembling small centipedes, having each of the abdominal segments provided with a pair of slender ciliated appendages employed as organs of respiration as well as of locomotion, while the last segment is provided with four hooked organs by means of which they leap about. III. Philhydrida, or Water-loving Beetles, are aquatic or subaquatic in their habits, being found in the water or on the moist margins of ponds and marshes. Along with the two following groups they feed on decaying animal and vegetable substances, and for this reason those insects have been classed together as Rhypopliaga, or Cleansers. The antennas are short and clavate, and they are specially dis tinguished from other aquatic forms by the great length of the maxillary palps, a feature which has procured for them the name Palpicornes, often applied to them. The best known forms belong to the family Hydrophilidce, of which one species, and that the largest, Hydroi)hi&amp;gt;us piceus (Plate VII. fig. 32), is an inhabitant of Europe. This beetle is oval in form, and of a dark olive colour, and measures H inches in length. It uses its hind legs for swimming or rather paddling, moving them not together, as the true water beetles do, but alternately. Its movements in the water are thus slower than those of the former, but speed in this case 13 less necessary, their principal food consisting of aquatic leaves. In the larval stage, however, //. piceus makes an approach to the true water beetles in its food, and is so ferocious as to have earned the name ver assassin on the Continent. The mode of respiration in the perfect insect is curious ; unable to raise its upper surface above the water, it merely protrudes its head, and folding its club- shaped antennae, the ends of which are slightly hollow, it thus conveys little bubbles of air beneath the surface of the water, where it brings them into contact with the tracheal openings. The larvae swim with facility, and are provided at the posterior extremity with two appendages which serve to maintain them at the surface when they ascend to breathe. IV. Necrophaya are the beetles of most service in re moving decaying animal matter, although a few species live on putrescent fungi, and others resemble the carnivorous groups in attacking and devouring the larvaa of other insects. They are chiefly marked by the form of the an tennae, which are not much longer than the head, and get thickened or club-shaped at the extremity. This group comprises the Sexton Beetles (Necrophorus), of which Necropliorus vespillo (Plate VII. fig. 27) may be taken as the type. These insects have thick bodies and powerful limbs, and owe their popular name to the peculiar manner in which they provide a nidus for their eggs. Their sense of smell is exceedingly acute, and no sooner does one of the smaller quadrupeds, as mice or moles, die, than several of those burying beetles, gathering about, begin to remove the earth from beneath the dead animal, and in a few hours succeed in sinking the carcase beneath the level of the ground, which they then cover over with earth. Having thus prevented the body from being devoured by other carrion-eating animals, or from having its juices dried up by exposure to the sun, they make their way into the carcase and there deposit their eggs. Several individuals generally work together in this grave-digging operation, although Necrophorus germanicus is said to labour alone, and they have been known to show considerable intelligence in performing this operation ; thua Gleiditsch states that in order to get possession of the body of a mole, fixed on the end of a stick, they under mined the latter and thus brought the dead body to the ground. The larvce on leaving the egg thus find them selves surrounded by an abundance of food ; and when full grown they bury themselves fully a foot beneath the surface of the ground, where they form an oval chamber, the walls of which are strengthened by a coating of a gluey liquid, and in which they undergo metamorphosis. Shield Beetles (Silpha) (Plate VII. fig. 22) so called from the flattened form of their bodies, feed chiefly on carrion ; some, however, climb upon plants, particularly the stems of wheat and other grain, where they find small helices on which they prey ; while others, as Silpha pundata, dwell on trees and devour caterpillars. They exhale a disagree able odour, probably arising from the nature of their food, and when they are seized a thick dark-coloured liquid exudes from their bodies. The Dermestidce are a family of small but widely-distributed beetles, which work great havoc among skins, furs, leather, and the dried or stuffed animals in museums. The perfect insects are timid creatures, which when disturbed fold their short contractile feet under their bodies, and, remaining perfectly motionless, admirably counterfeit death. The mischief is mainly wrought by the larvae. These shed their skins several times, and take nearly a year in attaining their full growth. One of the most common and injurious species of this family is the Bacon Beetle (Dermestes lardarius) (Plate VII. fig. 14) so called from its fondness for lard, but equally ready to attack the furrier s wares. Their tastes are exceedingly general, as they have been known to destroy a whole cargo of cork and even to perforate asbestos. The larvoe of Anthrenus museorum, a species not exceeding one- tenth of an inch in length, is exceedingly injurious to collections of insects, among which it eludes observation by its minuteness and by working in the interior of the speci mens, which are thus ruined before the damage is observed. V. Brachdytra (Plate VII. figs. 12, 15, 20) are readily