Page:Popular Science Monthly Volume 24.djvu/503

Rh but which widen as the larvæ grow, feeding themselves from the parenchyma in which they work, and at the same time obtaining a defense against external injurious influences and disturbances. They usually leave their burrow, when about to assume the chrysalis state, by a little hole that may be found at the extreme end of the excavation, and either fall to the ground or make a cocoon, attached to some plant, in the air. Other burrowing larvæ bury themselves in the ground.

For the preservation of the chrysalis, Nature has provided many insect-larvae with the faculty of spinning, and organs for the purpose. This function is so extraordinarily developed in the larvæ of the butterflies that a whole group of that order have been called "the spinners"; while many of these spinners—the silk-worms—have been made serviceable to human civilization. Before the spinning larva advances to its last change of skin, it selects a sheltered, dry spot—between leaves, on bark, in a hedge, in turf, or on a post—and then, drawing from the spinning-glands situated under its neck and between its head and fore-feet fine silken threads, it prepares an ample, firm, and intricate web of flock-silk for its envelope. Having completed its cocoon, it shakes off its old skin, and lays itself to sleep in this soft but solidly-made bed, while its pupa-skin hardens and it awaits the time for its next transformation; and only when disturbed from without does it show by some spasmodic motion of the posterior segment that it can still feel, and that its pupa-rest is not a death-sleep, but only a temporary repose. If the larva is provided with a hairy skin or bristles, they become interwoven with the cocoon, and a composite texture is formed, which man must be careful how he touches, or the bristles will sting his fingers and make them smart. Naked caterpillars, or larvae, weave, like the real silk-worm, cocoons of pure silk, or, like the false-caterpillars, and the larvae of wasps, ants, and bees, transparent, cylindric-oval envelopes of a consistency like that of parchment or waxed paper. The naked caterpillars of the Hermione moth make a kind of roof of pieces of bark over a hollow which they have excavated in the ground for their bed; and a hairy larva provides for itself in a similar manner. Many other larvae go for the security of their pupae into or upon the ground, where they prepare, from leaf-dust, moss, and grains of sand, a ball rough on the outside but smoothly finished within, or simply a hole in the ground, as an envelope.

Arrived at last at its perfect and free state, the insect is efficiently protected by that "mimicry" which has been much discussed by Wallace and other writers, or the likeness in color, and sometimes in other qualities, which it presents to objects that are associated with its most accustomed haunts. Some instances of this mimicry may be observed among higher animals, but it is most conspicuous and significant with insects. We need only refer to the appearance of