Insect manufactures

by Anonymous

When the caterpillar has attained its full growth, it is a very different creature from the little black worm which first issued from the egg, being from two and a half to three inches in length, and its body consisting of twelve membranous rings, which contract and elongate as the animal moves. It is furnished with sixteen legs, in pairs: three pairs in front, under the first three rings, are covered with a shelly or scaly substance; the other five pairs, called holders, are furnished with little hooks, which assist the insect in climbing. The head is covered with a scaly substance similar to the covering of the fore legs. The mandibles are of great strength, and indented like the teeth of a saw. Beneath the jaw are two small openings, through which the insect draws its silken lines. The substance of which the silk is composed is a fine yellow transparent gum, secreted in two slender vessels, “which are wound, as it were, on two spindles in the stomach; if unfolded, these vessels would be about ten inches in length.” The insect breathes by means of eighteen holes or spiracles, distributed along the body, nine on each side. On each side of the head, near the mouth, are seven small eyes; the two specks higher up on the head, which are generally mistaken for eyes, are only parts of the skull.

FULL GROWN SILKWORM.

When the silkworm is ready to spin, it gets upon the leaves without eating them, rears its head as if in search of something, or crawls to the edges of the tray and moves slowly along; its rings draw in, and its greenish colour changes to a deep golden hue; its skin becomes wrinkled about the neck, and its body feels like soft dough, and on taking it in the hand, and looking through it, the whole body has assumed the transparency of a ripe yellow plum. When this is observed, the owner of the insects puts each singly into a little cone of white paper, which he pins to the wall or elsewhere, so that the creature may be undisturbed at its work. But in the nurseries abroad little bushes are set up on the wicker shelves, and the insects mount them and form their cocoons among the twigs.

Supposing the worm to be left to itself on the tray, without either of these precautions, it at last selects some corner or hollow place which will conveniently hold the cocoon it is about to spin, and begins by throwing out a number of irregular threads, which are intended to support its nest. Upon these it forms, during the first day, a loose structure of floss silk of an oval shape, within which, during the next three days, it winds the firm, hard, yellow ball, remaining, of course, all the time within it. In this operation the insect does not greatly change the position of the hinder part of its body, but continues drawing its thread from various points and attaching it to others, so that after a time the body becomes to a great extent enclosed by the thread. “The work is then continued from one thread to another, the silkworm moving its head and spinning in a zigzag way, bending the fore part of the body back to spin in all directions within reach, and shifting the body only to cover with silk the part which was beneath it. As the silkworm spins its web by thus bending the fore part of the body back, and moves the hinder part of the body in such a way only as to enable it to reach the farther back with the fore part, it follows that it encloses itself in a cocoon much shorter than its own body, for soon after the beginning the whole is continued with the body in a bent position. From the foregoing account it appears that with the most simple instinctive principles all the ends necessary are gained. If the silkworm shifted its position much at the beginning of the work, it could never enclose itself in a cocoon; but by its mode of proceeding, as above explained, it encloses itself in a cocoon which only consumes as much silk as is necessary to hold the chrysalis.”

THE COCOON.
(A portion of the floss silk has been removed.)

The use of the cocoon, in the natural state of the insect, is to afford a warm nest, where, secure from the inclemencies of the season, and the attacks of enemies, it may undergo its final changes. The cocoon is made water-tight by an internal lining of gum, and the silken thread of which the ball is made is also smeared with a similar gum, which hardens in the air.

THE CHRYSALIS.