The Coleoptera (from [Greek: koleos], a sheath, and [Greek: pteron], a wing) are insects with four wings. The anterior wings, or elytra, are not used in flying; they are sheaths, more or less hard, sometimes varied with bright colours, and never crossing over each other. The posterior wings are membranous, presenting a ramification of veins, and usually folding up under the elytra, which protect them when at rest. The mouth of Coleoptera is provided with mandibles, with jaws, and two quite distinct lips, and is suited for mastication. They undergo complete metamorphosis. After an existence of greater or less extent in the larva state (in the case of the cockchafer three years), the insect changes into a pupa, which remains in a state of complete immobility. After a certain time, the pupa bursts its envelope and assumes the form of a perfect insect. The Coleoptera presents the utmost variety of habits as regards their habitations and food. One does not find in this Order those admirable instincts, those manifestations of intelligence, which bring certain Hymenoptera near to those beings which are highest in the animal scale; but they offer peculiarities very well deserving serious and profound study. Some are carnivorous, and thus they are useful to man in destroying other noxious insects, which they seek on the ground, on low plants, on trees, and even in the depths of the waters. Many of these Coleoptera feed on animal matter in a state of putrefaction. We may look on them as useful auxiliaries: they are Nature's undertakers.
A great number live in the excrements of animals. The dung of oxen, buffaloes, and camels afford shelter to Coleoptera of different families, which thus live on vegetable matter more or less animalised. Others attack skins and dried animals in general; and some are the pest of entomological collections. Lastly, immense legions of Coleoptera are phytophagous; that is to say, they attack roots, bark, wood, leaves, and fruits, and cause much annoyance to the agriculturist. Above all, the larvæ are to be dreaded. Those which live in wood may in a few years occasion the loss of trees, vigorous and full of life; or completely destroy the beams of a building. Certain larvæ, such as those of the cockchafer, eat away the roots of vegetables, and so destroy the harvests. Others, lastly, devour the leaves and the stalks of plants, attack the flowers in the gardens, or the corn in the barns; and so man makes desperate war against them.
In the immense variety of known Coleoptera we must be contented to choose those types which are most prominent and most characteristic. We will begin with the Scarabæides, with their heavy compact body, and short antennæ, terminated by a foliaceous club. It is to this tribe that belongs the beautiful Rose Beetle (Cetonia aurata), which lives on roses; the Cockchafer (Melolontha vulgaris); the Scarabæus of the Egyptians; &c.
This is the most interesting tribe of the whole Order Coleoptera. It corresponds with the great division of the Lamellicornes of Latreille. This name of Lamellicornes was intended to remind us of the arrangement into laminæ, more or less close together, of the club of the antennæ of these insects. Many Scarabæi have their mandibles membranous, or at least partially so, and always small. This peculiarity corresponds to their habits. Never, indeed, have they to triturate hard bodies; they all feed either on flowers, on leaves, or on stercoraceous matter. Their larvæ resemble each other much, even those of families very widely differing from each other in the perfect state. They are large, whitish worms, with diaphanous skins, scaly heads, furnished with toothed mandibles, living in the ground or in rotten wood. The pupæ are fat and stumpy, and they already show the features of the perfect insect. They make a chamber in which to undergo their changes. They remain generally three years in the larva state. The duration of the pupa is very short, as also is that of the perfect insect. The differences of the sexes are often very marked on the exterior, by protuberances, horns, &c., which constitute the distinctive ornament of the males.
In the group of Scarabæides we shall have to speak, above all, of the Cetoniadæ, the Chafers, and the Scarabæi properly so called. The family Cetoniadæ is one of the most remarkable, on account of the beauty of the insects which compose it and of the richness of their metallic lustre, some being of great splendour, and others having velvety tints. The larvæ live in wood in a state of decomposition; the perfect insects frequent flowers, and like the sun.
Fig. 423.—Rose Beetle (Cetonia aurata).
This family contains a great number of species, the type of which is the Rose Beetle (Cetonia aurata), of a beautiful green colour shot with gold, with transverse whitish lines. The rose beetle frequents roses especially, of which it eats the petals and the stamens. It is the Golden Melolontha of Aristotle, who tells us that this unfortunate insect shared with the cockchafer the privilege of amusing children. The Cetonia flies by day and by night, making use of its inferior wings without opening the elytra ([Fig. 423]). When seized, it pours out from the extremity of its abdomen a fœtid liquid, the only means of defence the poor insect possesses. The larva ([Fig. 424]) much resembles the larva of the cockchafers, but the legs are shorter. It is found in rotten wood, and often in ants' nests. When it has acquired its full development it makes a cocoon of an oval form ([Fig. 424]), in which it transforms itself into a pupa; the cocoon is composed of bits of wood agglomerated with a silky matter which the larva secretes.