The term "insect" has unfortunately been loosely employed in popular parlance to include such diverse beings as coral-polyps and house-flies. As the name itself indicates, it is properly applicable only to such animals as are more or less distinctly divided into segments. All true insects, in fact, are plainly divisible in their perfect state into three portions, the head, thorax, and abdomen. The most important classes in this portion of the animal kingdom are distinguished by the characteristics of their wings, and are—
I. Coleoptera, or those possessing crustaceous sheathing wing-covers, including all the beetles.
II. Orthroptera, having the wings when at rest in straight longitudinal folds, comprising such families as the earwigs, cockroaches, grasshoppers, and locusts.
III. Neuroptera, nerve-winged, characterised by four naked, strongly reticulated organs of flight, as seen in dragon-flies, may-flies, and white ants.
IV. Hymenoptera, membrane-winged, resembling the Neuroptera in some respects, but with fewer reticulations, and their organs of flight when in use are hooked together along the margins, so as to expose a continuous surface. Another distinguishing character is the appendage at the tail, in the form of either a sting or an ovipositor. The chief representative families are the bees, wasps, gad-flies, ants, and ichneumons.
V. Lepidoptera, having the wings covered with a scale-like powder, set like the tiles of a house. The butterflies and moths all belong to this order.
VI. Diptera, or two-winged insects, embracing the gnats, "daddy-long-legs," blow-flies, and house-flies.
Less important are the Homoptera, which have the wings of the same consistence throughout, as the aphides or blight-insects.
The Heteroptera, having the fore-wings coriaceous (or leathery) at the base and membranous towards the extremity. These comprise the bug tribe; while fleas belong to the Aptera, or wingless insects.
Insects pass through four stages during their lifetime: the egg, the larva, the pupa, and the imago conditions. The honey-bee exists in each of these states.