The body of the caterpillar contains nearly all the organs of the adult butterfly or moth. Respiration goes on through nine spiracles on each side, two on each ring. except the second, third. and last. There are no external traces of sexual organs, but there arise, during this stage, the 'imaginal disks,' which develop into the wings and legs of the adult insect. These rudiments of wings exist even in very young caterpillars as a thickening and bagging in of the hypodermis. Into this bag, trachea and blood make their way. dust how these internal wings reach the outside is not known: probably by the destruction of the outside hyptierinis. If the wing-membrane breaks during development, so that the blood or it emolympli exudes, the injured wing, will be smaller or deformed. Sometimes the wings fail to expand properly because they dry too soon, and a wet sponge mulct. a bell-jar. with trans forming Lephloptera. will aid in the production of perfect specimens.
Fording Habits and Mischief.—Caterpillars find themselves at birth in contact with propel him], and begin at once to devour it. and to obey certain other instincts necessary to their life and prosperity. This is the stage in which the but terfly or moth gets most of its nourishment and growth, none taking food in the next or pupal stage, and many not feeding at. all, as imagos.' The great majority are vegetable-caters, many being limited to it particular kind of plant, or to a few nearly allied plants. Some feed on flowers, some on seeds, some on roots. and some even on the woody portions of stems: some on wool, hides, furs, and other animal substances; a few' on lard. and other kinds of fat. Some feed in the dark. and some in the light. Some kinds seem to cat almost incessantly, hut most of them have alter nate periods of ravenousness and quiescence. As many of the favorite food-plants have been cul tivated by civilized man, and other substances eaten by these creatures have been made use of by him, he has multiplied by his operations the supply and consequently the numbers of certain species until they have beeome pests, destruetive of his work and profits. It is in the caterpillar stage that almost all the destructiveness of the Lepidop tern. is accomplished. On certain years they suc ceed in denuding whole forests or many fields. The cutworm, the artny-worm. and the cotton-worm are well-known pests. Their voracity is remarka ble. According to Trouvelot, when a Polyphemus caterpillar hatches. it weighs one-twentieth of a grain. and when it is 50 days old, it weighs 207 grains, and has consumed 120 oak-leaves, weigh ing threc•fourilis of a pound. "So the food taken by a single silkworm in 56 days equals in weight 80.000 times the primitive weight of the worm. What. a destruction of leaves this sin gle species of insects could make if only a one hundredth part. of the eggs laid came to matur ity! A. few' years would be sufficient for the propagation of a number large enough to devour all the leaves of our forests." Taken as a whole, caterpillars are economically so injurious that were it not for the great de pletion of their numbers by their multitudinous foes, they would soon destroy the vegetable king dom. They injure, or even kill, shrubs and trees, as well as all sorts of garden vegetables. They eat woolen stuffs of all kinds and furs. To offset all their destructiveness, they otter little save silk that is, at present at least, known to be use ful to man. There are a few species that are
helpful to vegetation, such as the Lycsenida, which feed on plant-lice and scale-insects. One such species (Feniseca Tarquinius) occurs in the United States. A few forms are aquatic and feed on plants under water.
Self-Protection in Caterp i a r S.—The Skin of some caterpillars is naked, that of others is cov ered with hairs. spines, or tubercles. Most are solitary. but some make for themselves nests or tents of silk. under which they dwell in societies, protected from the inclemency of the weather. Many construct cases or sheaths by agglutinat ing various substances together, as the caterpil lar of the common clothes-moth. Some roll to gether leaves, and fix them by threads, so form ing a dwelling for themselves; and a. few bur row and excavate galleries in the substance of leaves or in the pith of plants. Most of them are in color brown or green, while those hidden in galleries are whitish; but many carry gaudy colors and numerous ornamental or strange pro tuberances. All these characteristics are con nected with Nature's effort to protect them from their enemies. Alfred Russel Wallace has made clear the fatality to caterpillars of even slight wounds, for "a slight wound entails great loss of blood, while a modest injury must prove fatal." Therefore devices that enable caterpil lars to escape the notice or the attacks of ene mies are very useful to them. Many caterpillars possess a disagreeable smell, or a nauseous taste, or both. Thus, those of the swallow-tailed but terflies "are provided with a bifurcate or forked organ, generally yellow in color, which is pro truded from an opening in the skin back of the head, and which emits a powerful odor; this protrusive organ evidently exists only for the purposes of defense." Most caterpillars resist an attack by hurling their bodies violently from side to side. Others assume startling attitudes, or have a surprising arrangement of color. These terrifying, attitudes may accompany disagreeable tastes and so serve more vividly to impress upon the foe the unpleasant quality of the prey. Nevertheless, as Professor Poulton has stated, hungry animals may come to eat and like dis tasteful caterpillars. Certain caterpillars es cape the enemy by resembling the color of the background, concerning which more is to he said elsewhere. Others, such as the geometrids or measuring s, may combine with this pro tective coloration the capacity of attaching them selves by the hind end and stretching out iu the air like a twig. This rigid attitude they may maintain for some time. imitation may even be carried to the length of mimicking other kinds of animals. Thus the huge eye-spots. peculiar and marks on the anterior end give some forms the appearance of snakes or other strong animals. The odor of caterpillars is due to two sourees: (1 1 Pigment gained from the food ; 12) pigment inherent in the deep-lying tissues or skin. Most green caterpillars seem in some way to be col ored by the chlorophyll of the food-plant. Yel low is derived mainly front xanthophyll of plants. figment derived from food-plants tends gradually to give the caterpillar the coloration of the surroundings. See PROTECTIVE COLORA TION; MIMICRY; etc'.