THE COCHINEAL.
There are several species of these insects, alike in form and habits, but not alike useful. Some, as the Scale insect, are a great annoyance to gardeners, and destructive to our house plants. Others, as the Wax insect, live on certain tropical trees, and soon entomb themselves in a mass of glutinous matter that oozes from the small twigs of the tree, and which furnishes them both food and shelter. As they are marvelously prolific, a single female, according to the estimates of entomologists, being succeeded by many millions of descendants in less than a year, when a colony has possession of a tree, every tender branch is soon punctured, and the abundant resinous juices that flow out envelop it in a coating often half an inch thick. These branches, and also what falls to the ground, are collected, and the wax, melted off, is prepared for the market. From this source the shellac of commerce, so extensively used, is obtained. This curious and useful insect, like its congener, the cochineal, secretes a coloring substance, but of different tints, and less valuable. The Lac insect is a native of Siam, Assam, Burmah, Bengal, and Malabar. For some years the average annual imports into Britain have been a little over 600 tons of the lac dye, and more than a thousand tons of lac, including the several varieties. This industry also gives employment to many thousands of people.
METAMORPHOSIS OF A BEETLE.
Ex.—A, larva; b, pupa; c, beetle.
IV.—Coleoptera[20] (sheath-winged). Beetles are innumerable, about ninety thousand species being recognized. Their anterior or upper wings, useless for flight, are composed of a hard, horn-like substance known as chitine, and meet in a straight line on the top of the back. The posterior wings are thin, membranous, and, when folded, out of sight. They have usually two pairs of laterally moving mandibles, or jaws, and in their development undergo several metamorphoses. We see the egg, the larva, or grub, in different stages of its growth, the chrysalis, and the imago,[21] or complete beetle. Entomologists have spent much time and labor in making collections, and classifying them according to their peculiarities of form or habits. If many are repulsive, and most plain in form and color, some are beautiful, and worthy of our admiration. Beetles, especially in their larva stage of development are very voracious, and as most of their species live on fruits, leaves, and stems of plants, they are often destructive of crops, and even of forests. Millions of vigorous, valuable trees have been assailed, and stripped of their leaves fast as they appeared, or literally bored to death. All know the ravages of the potato beetle on our American tuber, that has to be assiduously defended to prevent the entire destruction of the crop. Some known as Goliath and Hercules beetles are large, often measuring six inches in length, exclusive of their long antennæ. The “Diamond beetles” of Brazil are adorned with the most brilliant colors, showing a beautiful metallic luster, and the elytra,[22] or chitine sheaths, of this species are now largely used in the manufacture of personal ornaments.[23]
V. Diptera (two-winged), or Flies, number about 24,000 varieties. Among these are the Mosquito, Hessian fly, Daddy-long-legs, Flea, and common House fly. They usually have one pair of fully developed wings, the second pair being rudimentary, although a few, as the fleas, are wingless. They pass through a complete metamorphosis, the larvæ being usually footless maggots, with the breathing holes in the posterior part of the body; the pupa are either encased in the dry skin of the larvæ or are naked.
VI. Lepidoptera[24] (scaly-winged), or Butterflies and Moths, are distinguished by four wings, covered on both sides by minute scales. The butterflies fly by day and have knobbed antennæ, while the moths fly by night and have feathery antennæ. Among the moths one of the most interesting is that of the silk worm.[25] The physiology of the insect and its metamorphoses reveal nothing very peculiar, and its habits need not be mentioned farther than to say, the larva eats voraciously, with short intervals of abstinence, until full grown, which stage is reached in about a month. During the last ten days the silk germ is elaborated, the eggs laid, and then the spinning and winding soon begin. To complete the cocoon requires at most only about three days. The larva then becomes a chrysalis, and in due time the moth emerges from its cell.
VII. Hymenoptera (membrane-winged) comprises the Ichneumon and Gall fly, Ants, Wasps, Bees, in all about 25,000 species. This order includes the most social of the insects. They have four wings, which in flying they fasten together by means of small hooks on the edges. The females are usually provided with a sting or borer. The Gall fly produces the gall nuts or oak balls so common on oak trees. The Ichneumon fly introduces its eggs underneath the skin of the caterpillar.[26]