Closely allied to these forms are the fleas (Fig. 228), which are at once interesting and irritating. They are wingless, and have two simple eyes. The larva resembles a small caterpillar. It attains its growth in twelve days, then enters a small cocoon, which it weaves. There it remains for sixteen days, when it breaks forth a full-grown flea. Of all insects the fleas are the most amenable to instruction. Some years ago a flea circus was one of the attractions of New York, where, by looking through a magnifying glass, one could see fleas dragging chariots with other fleas dressed as cavaliers sitting on the seats. Many other seemingly impossible feats were exhibited. XXVII. THE BUTTERFLIES AND MOTHS Of all the insects the butterflies (Fig. 229) are the most beautiful. Nature has arrayed them in coats of many colors. Every tint and every possible shade of color, including metallic, is found among them. In some of the South American forests they are of gigantic size, a blaze of iridescent blue, as though formed of the most delicate flakes of that beautiful mineral labradorite. [Illustration: FIG. 229.--A butterfly.] The butterflies add to the beauty of nature. Among the trees they congregate, forming dashes of color, red, blue, green, and golden yellow. They vie with the flowers in their splendors; besides being ornamental they accomplish a great work in carrying pollen from flower to flower and from plant to plant. They have small heads (Fig. 230), short antennæ, and four beautiful wings which are covered with minute scales. Each of the latter when examined under a microscope becomes a resplendent object, glistening like the plate of some gorgeous armor. The mouth parts are adapted for sucking, and are coiled up when not in use (Fig. 231). They consist of two tubular or hollow threads. [Illustration: FIG. 230.--Head of a moth.] [Illustration: FIG. 231.--Mouth parts of a butterfly.] The ordinary caterpillar is the larva of the butterfly. The eggs are deposited on leaves and various places, and soon hatch into caterpillars (Fig. 232). These lead a predatory life for some time, doing a vast amount of damage, almost every plant having its peculiar pest. Some affect one tree, some another. The famous elm trees of many of the New England cities have more than once been threatened by these larvæ. They shed their coats several times. The caterpillar finally merges into the chrysalis, from which it escapes as the perfect insect. All of these changes can easily be observed by keeping a caterpillar under continuous observation. The butterflies have well-developed legs, but they rarely use them for locomotion, preferring to fly from flower to flower. The tortoise-shell butterfly is a familiar form (Fig. 233), its marvelous colors resembling this shell. Some have an under covering of pure silver. Another conspicuous form is the white butterfly (Fig. 234), which, as its name suggests, is pure white, with several black spots.