Insects are easily distinguished from the other jointed animals by many salient characters. They have one pair of antennæ, two large compound eyes, composed of a great number of facets, and sometimes one, two, or three simple eyes placed on the crown or front of the head. In its adult condition an insect is composed of three different parts, which can be most readily noticed in a wasp. There is the head, with the antennæ and mouth-parts; the thorax, to which one or two pairs of wings are attached above, and three pairs of legs below; and the abdomen. Insects breathe through openings, called "stigmata," in the sides of the thorax and abdomen. They never possess more than six legs in the perfect state, the abdominal legs present in caterpillars, etc., disappearing in the adult condition. They generally pass through what is called a "metamorphosis,"—four different stages of life, called respectively egg; larva or caterpillar; pupa, nymph, or chrysalis; and imago, or perfect insect.
Insects are divided into several large sections, of which the following seven are the most important, and many entomologists prefer to include all insects under them:—
Sheath-winged Insects, or Beetles; Straight-winged Insects, or Earwigs, Cockroaches, Soothsayers, Stick-insects, Crickets, Grasshoppers, and Locusts; Nerve-winged or Lace-winged Insects, or Dragon-flies and their relatives; Stinging Four-winged Insects, or Ants, Bees and Wasps, and their allies; Scale-winged Insects, or Butterflies and Moths; Half-winged Insects, or Bugs and Frog-hoppers; Two-winged Insects, or Flies.
We proceed to notice these orders separately.
SHEATH-WINGED INSECTS, OR BEETLES.
BY THE REV. THEODORE WOOD, F.E.S.
Beetles are distinguished from most other insects by the fact that the front wings are not employed in flight, but are modified into horny sheaths, which cover and protect the lower pair while not in use. This arrangement, however, is also found in the Earwigs as well as in the so-called "Black-beetle" and its allies, and it is to be noted that the wing-cases of beetles lie evenly side by side together when the wings are folded, while the folding of the wings themselves is transverse as well as longitudinal. The number of species is very great, upwards of 100,000 having already been described, of which about 3,400 have been taken in the British Islands.
The order is again divided into several smaller groups, first among which stand the predaceous beetles of the land. Of these the common English Tiger-beetle is a familiar example. It is found on sandy and peaty heaths, and may be known at once by its bright green wing-cases, marked with white spots, and the metallic blue of the abdomen. The legs are coppery. It flies with great swiftness in the hot sunshine, taking to wing as readily as a blue-bottle fly, and feeds entirely upon other insects.
Another representative of the group is rich golden green in colour, with coppery reflections. It is only an occasional visitor to Britain, but abounds in France and Germany, where it feeds upon the caterpillars of the famous Processionary Moth, and is largely instrumental in checking their ravages in the great oak forests.
