Caterpillar, the common name of the larva) of lepidopterous insects, including butterflies and moths. Caterpillars vary greatly in form and appearance, as may be judged from the fact that about GOO species are known in New England alone, and probably many are yet unknown. The body is composed of 13 segments; the first constitutes the head, containing the jaws and oral appendages; the second, third, and fourth form the thorax of the future insect, and the remaining ones make up the abdomen. The head is rounded, and of a harder consistence than the body; on each side are six very small ocelli, or simple eyes, with a very convex cornea and a spherical crystalline lens, two short antenna?, and a mouth, with strong jaws moving transversely; the mandibles are hard, for breaking up the food, while the maxilla) are soft and adapted rather for holding it; in the middle of the lower lip is a conical tube, through which issue the silken threads from which their nests and cocoons are made, and their suspensory fibres; a viscid fluid, enclosed in two long and slender bags, is poured out through the "spinneret" in a line stream, and hardens into silk on contact with the air.
The segments of the body are very nearly equally developed; the second, third, and fourth have each a pair of tapering, jointed legs, covered with a shelly skin and ending with a little claw; these are the rudiments or cases of the future limbs, and are the true organs of locomotion; some of the other segments are furnished with soft, joint-less, fleshy, and contractile legs, called prop legs, which disappear with the larval condition, being only prolongations of the external covering and shed with it, like the nails and claws of the higher animals; the abdominal legs vary in number from four to ten, and are provided around the margin of the sole with rows of minute hooks capable of such direction as is necessary for a secure hold. The body is in some cases smooth, in others hairy, and even spiny; these external appendages, whether for ornament or defence, are shed with the skin before the pupa state. Where the middle portion of the body is unprovided with feet, the caterpillar adopts the arched or looped manner of walking, so familiarly known in the common canker worm; these species are hence called spanners, loopers, surveyors, and geometers; some, when in a state of repose, fix themselves by the hind legs only, and project in a rigid condition from branches, which they then much resemble in direction, form, and color; the power of remaining thus immovable for hours at a time must be due to a muscular force of which we have no idea in vertebrated animals; the species which have eight to ten intermediate feet walk by short steps, in a continuous worm-like manner.
Some smooth caterpillars, as those of the sphinx moth (commonly called potato worm), have a spine or thorn upon the top of the last segment of the body, directed backward and curved; though this looks like and has been considered an offensive or defensive weapon, its softness is such that it could inflict no wound. The larvae of some of the hymenopterous insects, as of the saw flies (tenthredinidae), resemble caterpillars both in form and habits; but these false caterpillars may be distinguished by their greater number of legs (18 to 22), and by the absence of the numerous hooks in their prop legs; the larva) of other insects, having the same number of segments, are scaly and not soft and membra-nous. On each side of the body are nine oval apertures, spiracles, or stigmata, situated in the second, fifth, and following segments to the twelfth, provided with valves; these communicate directly with the internal respiratory organs, which are in the caterpillar branching tubes; in the perfect insect, the trachea' are dilated into an immense number of vesicles permeating every part of the body. The intestine is short and straight.
The nervous system is a series of ganglia connected by chords, one for each segment, the greater part of it in the perfect insect being concentrated in the head and thorax. Caterpillars vary greatly in size; the mean may be taken at an inch, those much exceeding this being large, while those much below it may be considered small; those which have only eight feet in all are the smallest, and are generally the moths' caterpillars. The size of a caterpillar compared to that of the egg is very great, and the rapidity of its growth is truly astonishing; there is no large animal at all comparable to it for voracity, for some species will eat in 24 hours more than double their own weight; though less voracious than locusts, they are quite as destructive from their greater fecundity and their wider distribution over the vegetable world. According to Count Dandolo, the common silkworm, during the 30 days in which it attains its full size, increases in length from 1 to 40 lines and in weight from 1/100 to about 95 grains; during this period, therefore, it has increased 9,500 times in weight, and has eaten 50,000 times its weight of food.
The caterpillar of the privet hawk moth on leaving the egg weighs about 1/80 of a grain, and at the end of 32 days, when it has acquired its maximum size, it has been known to weigh 142 grains, and to measure over 4 inches in length, thus increasing more than 11,300 times its original weight. According to Lyonnet, the larva of one of the carpenter moths (cossus ligniperda, Fabr., or genus xyleu-tes of Newman), during the three years in which it is supposed to remain in the caterpillar state, increases 72,000 times its first weight by a great accumulation of fat for its nutriment in the pupa and perfect states. Most caterpillars feed on vegetable substances, the leaves, flowers, roots, buds, seeds, and even the wood of plants; many domestic pests gnaw woollens and furs, leather, and fatty substances; while some are quite exclusive in their diet, others are more indiscriminate feeders. When they are very numerous, scarcely any plant escapes their attacks, and at such times their ravages are deplorable, reducing trees in midsummer to their winter leafless livery. Plants with acrid juices are the favorite food of some species, and the nettle and other spiny shrubs are the natural habitats of many smooth and tender-skinned varieties.
Most feed on the exterior of plants, but some of the most destructive and most delicate live in the interior of branches and stems. The sweetest fruits, as pears, plums, and apples, ripen and fall prematurely, the abodes of caterpillars; plums are especially liable to be thus inhabited, while the peach and apricot are free from all larva); it has been observed that a single fruit rarely contains more than a single caterpillar, the second inhabitant, if there be one, being the larva of some other order of insects. Wheat, rye, barley, and other grains are infested by small caterpillars, which gnaw away the whole interior without any external perceptible trace, so that an apparently sound heap may be only a collection of useless skins; a single grain contains just the quantity of provision necessary for the transformation of the insect. Another example of the instinct of the lepidoptera is seen in the fact of their depositing their eggs on the parts of the plant which will furnish an easily accessible supply of food to the caterpillar when it is hatched; their eggs are found glued to fruits, and to flowers that are to produce fruits, between the very petals, so that the young find themselves surrounded by an immediate supply.
Caterpillars are remarkable for the eagerness with which some species will feed upon their fellows, in preference to vegetable substances in profusion around them. Different species select different times of day for feeding; some eat at all hours, some in the morning and evening, and others only at night; a knowledge of these habits is of great advantage for the easy destruction of many pests of the vegetable garden. Though generally disgusting objects, the contrast and brilliancy of the colors in some of them are eminently beautiful. Some species herd together in great numbers, constructing their silken habitations in common; others live solitary, exposed to light and air, or protected in rolled leaves or silken sheaths; others burrow in the ground, or conceal themselves in the stems of plants and the pulpy substance of leaves. The caterpillars which live in one nest all come from the eggs of a single insect, and are generally hatched on the same day; from 200 to 700 may thus be found together, and may remain so through the chrysalis condition, or may separate at different periods of life; some, though living in great numbers on the same tree, are solitary with respect to each other, performing no work in common; the most solitary are the leaf-rollers, which are also the most remarkable for their vivacity.
For the mechanism of the various abodes of caterpillars the reader is referred to the works of Reaumur, Latreille, Kirby and Spence, and other practical entomologists. The attitudes assumed by caterpillars when attempts are made to catch them are characteristic of species in many cases; some roll themselves into a ring and remain as if dead, the hairy ones resembling little hedgehogs; others fall instantly to the ground and try to escape by rapid flight; some attempt to defend themselves by various motions of their bodies. The mode of marching adopted by the "processionary caterpillars" is very remarkable; these live in society, and when they quit their nest they go in a regular procession, a single caterpillar first and the others in single file, or two, three, and four abreast; the line is so perfect in the columns, that the head of one is never beyond that of another in the row; following their leader, stopping when he stops, they make journeys from tree to tree in search of food, returning to their nest in the same order; they form their ranks, march, and halt, with the precision of soldiers; when several nests are in the same wood, the spectacle of these creeping battalions, issuing forth and returning at the same hour, is exceedingly interesting; 'the processions generally take place toward night.
Another species, common in pine forests and living together, walk in procession in single file, often very long, the head of each in contact with the tail of the one in advance; they defile in a straight line, or in a variety of graceful curves; they sometimes go to great distances from the nest, always with the same slow and grave step, following exactly their leader; they return to the nest by the same path, which they find not by the sense of sight but of touch; the path of exit is covered as they go by a silken tapestry, and they return upon the same delicate carpet, however tortuous may have been their way. Caterpillars change their skins several times before attaining their perfect state, spinning for themselves a sort of cocoon of silk, interwoven with hairs of their own, with bits of leaves, and even with particles of earth, suspending themselves by silken threads, or burying themselves in the ground. (See Butterfly, vol. iii., p. 495.) Those lepidop-tera which pass the winter in the egg live in the caterpillar form during a part of the summer; the eggs are protected against cold by the shell and by the sheltered or subterranean situations in which they are placed; others pass the winter as caterpillars, concealing themselves under stones and the bark of trees, or descending dee]) into the ground where the cold cannot reach them; the social varieties retire to their warm and water-proof nests; these come forth in the spring quite well grown, but most pass the winter in the form of chrysalis, in protected or in open situations; a few pass this season as perfect insects.
The natural enemies of caterpillars are numerous; almost all insectivorous birds and poultry devour them eagerly; other insects not unfrequently feed upon them; and little maggots developed in their bodies from the eggs of the ichneumonidae cause thousands to perish prematurely. In the northern states there are about 1,000 different kinds of butterflies and moths; as each female lays from 200 to 500 eggs, these species, from a single female each, would on an average produce in a year 300,000 caterpillars; if one half of these were females, the second generation would be 45 millions, and the third 6,750 millions; with such fecundity it may well be imagined that the destructive powers of caterpillars must be very great. The work of Dr. Harris on "The Insects Injurious to Vegetation," under the head of "Lepidoptera," gives an extended and valuable account of the ravages of caterpillars in America, particularly in New England. Alluding to laws in France and Belgium which require the people to "uncaterpillar" their gardens and orchards, under the penalty of a fine, he thinks similar regulations might be enacted here with advantage, or at least that the towns might offer a respectable bounty for caterpillars by the quart, thus affording remunerative and highly useful employment to children and otherwise idle persons. - For notices of many destructive caterpillars see Hawk Moth, Moth and articles under the popular names of the most noted species.
1. Smooth Caterpillar (Asterias). 2. Hairy Caterpillar (S. acroea). 3. Spanner (Geometra).