Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/152

128 the leaf of an aquatic plant or leave it to float on the surface of the water. Certain species of the Weevil tribe deposit their eggs on the leaves of trees, splitting the median nervures in several places, and afterwards rolling them up. In its progress from the egg to the perfect insect the beetle undergoes complete metamorphosis, passing from the larval to the pupa stage, and remaining totally quiescent during the latter. Coleopterous Iarva3 generally consist of 13 segments, of which those forming the head and thorax are usually of a hard horny texture, the mouth, as in the perfect insect, being masticatory, and the eyes, when present, simple, or ocelli. They have usually six legs, and prolegs, as in caterpillars, are occasionally present; but the larvre of many species are legless grubs, while in others the limbs are but feebly developed. In those groups in which the elytra are abbreviated, the larvae are exceedingly active and closely resemble the perfect insect. Like their parents the larva; of beetles feed on living animals, on plants, or on decaying animal and vegetable substances, but greatly exceed the perfect insect in the quantity of food which they consume, and it is in this condition that beetles do most injury to field crops and forest trees. The larvae of burrowing beetles, known as " White Worms," spend their existence in the earth, and are destitute of eyes; those of the Stag Beetles and other wood-boring groups live in the trunks of decaying trees ; mealworms the larvae of Tenebrio molitor live enveloped in flour, and those of the Corn Weevil in the heart of the wheat grain ; while those of another species of Weevil make their homes in the fleshy parts of the receptacles of composite flowers. The larvae of Oil Beetles (Meloc), or at least certain species of them whose life-history has been observed, after leaving the egg, which the perfect insect has deposited just beneath the surface of the ground, climb upon the stems of plants, and take the first opportunity of attaching themselves to any insect that may happen to alight near them, and in this way they are occasionally conveyed into the hives of bees, in which alone they meet with their appropriate food. Only a few of them are thus fortunate, the majority of the larvae getting attached to the wrong insect, and so perishing of hunger. The species probably owes its preservation to the great number of eggs, amounting to upwards of 4000, deposited by a single female. The larva? of one group of water beetles, Hydrophilus, swim readily by means of their ciliated legs, those of another group, Dytiscus, make use also of their flexible abdomen provided at its extremity with a pair of leaf-like appendages (Plate VII. fig. G) ; w r hile the Whirligig larvae (Gyrinua), in addition to ciliated swimming organs, are provided with four movable hooks on the posterior segment, by which they are enabled to take extensive leaps (Plate VII. fig. 17). The duration of the larval state varies in different groups of beetles, being comparatively short in leaf-eating species, but lasting for three or four years in those which burrow in the earth or in wood. The larvae in the latter case pass the winter in a torpid state, abstain ing almost entirely from food, until awakened from their temporary trance by the return of genial weather, when they greedily attack their favourite food, and grow rapidly. In passing from the condition of a larva, the beetle does not, like the butterfly, assume a form altogether different from that of the perfect insect, but in the pupa or nymph state shows all the parts of the future insect, only in a condi tion of almost complete immobility. In preparing for this quiescent period, the larvae of many species surround themselves with a cocoon, consisting, in the case of the Scaralioeidce, of earth and small pieces of wood glued together with saliva, and in that of the Goliath Beetles, of mud. Others resemble the larvae of moths in constructing tubes in which to undergo their transformations, while the Jarvae of Lady-Birds Coccinrtla suspend themsalves by 8500 970 529 2686 7576 the tail and make use of their larval covering as a protec tion to the nymph within. When the condition of nymph is assumed in autumn, no further change takes place till the ensuing spring, but under suitable conditions of heat this stage does not last usually for more than three or four weeks, after which it emerges a full-blown beetle. The number of known species of beetles is estimated at J0,000, and these are probably not more than one-half of the total number in existence Great Britain alone possessing 3614 indigenous species. They occur in greatest abundance in the wooded parts of tropical regions. " A large proportion of the beetles of the tropics," says Wallace, " are more or less dependent on vegetation and particularly on timber, bark, and leaves in various stages of decay. In the untouched virgin forest the beetles are found at spots where trees have fallen through decay and old age." The number gradually decreases towards the poles, only a few species occurring as far north as Greenland. The six zoological provinces proposed by Mr Sclater in 1859 as applicable to the existing distribution of birds, have lately been shown by Mr A. R. Wallace, in his admirable work on the Geographical Distribution of Animals (1876), to mark off equally characteristic groups of Coleopterous insects, a conclusion arrived at from a study of the distribution of the following six important families : Cicindelidce or Tiger Beetles, containing 35 genera and 803 species. CaraLida; or Ground Beetles, 620 8500 Cctoniidrc or Eose- Chafers, 120 LucanidiE or Stag Beetles, 45 Buprestidse or Metallic Beetles, 109 Longicornia or Long-horned Beetles 1488 The Palaaarctic Region, which comprises Europe, Africa north of the Sahara, and Northern Asia, possesses about 20,000 species of beetles, and is specially characterized by abundance of Carabidce, nearly two-fifths of the entire number belonging to this region ; Longicorns are also well represented by 196 genera, of which 51 are peculiar to it. The Coleoptera of the Canary Islands, Madeira, and the Azores are Palaearctic, but are peculiar in the total absence of such forms as the Tiger Beetles, the Chafers, and the Rose-Chafers, also in the great number of wingless species. The latter are specially numerous in groups of beetles peculiar to those islands, but they also occur in other cases, 22 genera which either usually or at least sometimes are winged in Southern Europe having only wingless species in Madeira, while at least three species winged in Europe occur in those islands in an apterous condition. On the other hand, those species in Madeira which possess wings have them more largely developed than they are among allied continental forms ; the strong-winged and the wing less thus appearing best suited to live in islands exposed, as these Atlantic groups are, to frequent storms. The Ethiopian Region, which includes Africa south of the Sahara and Madagascar, is specially rich in Cetoniidce, possessing 76, or more than half of the known genera, with 64 of these peculiar to it, of which no less than 21 are found exclusively in Madagascar. It has also 262 genera of Longicorns, 216 of which are peculiar. The Oriental Region, comprising Southern Asia and the islands adjacent, contains some of the most remarkable forms of Carabidw, as Mormolyce <pliyllodes, and is rich in gorgeous metallic beetles (Huprestidce) and in Longicorns, having 360 genera of the latter, with 70 per cent, peculiar to it. The Australian Region shows affinity with the Oriental in its Coleoptera ; it is equally rich in peculiar forms of Longi corns, and is the richest of all the regions in Bvprestidce, having 47, or more than one-half of the known genera, and 20 of these confined to it. Several genera belonging to this and other families have their species divided between

the Australian and Neotropical or South American Regions,