struyyle for Fxistenee,—Onlv a few out of the vast hosts of caterpillars ever reach maturity. Many are destroyed by cold. wet, drouth, or lack of food. Vast numbers fall prey to birds, reptiles. and mammals. Many others are caught by wasps and stored up as food for the young. or are cap tured by adult and larval predaceous beetles. Ich neumon flies deposit their eggs within great num bers of caterpillars, where they develop and eventually kill the caterpillar or pupa. Tachina flies also lay their eggs on caterpillars and the larva- are parasitic within them. In addition, caterpillars are subject to fungus and various other contagious diseases which are particu larly fatal to the cultivated silkworm.
Molting.—Saon after the caterpillar begins to take food and increase in size, it is obliged to shed its skin, which has become too tight. To take its place. a larger, soft one is developed be neath the old one. This new skin becomes, in its turn, too tight and 'inelastic, and must be shed. A number of such moltings or ecdyses take place before the embryo attains full size. These normally occur at regular intervals, and four or five molts complete the growth; but "in cases where caterpillars hibernate . . . a long inter val necessarily elapses. Some .Arctic species are known in which the development from the e,ssg to the perfect insect covers a period of two or Three years." The manner in which the molt ing is effected is very interesting. When the necessity is felt, the caterpillar ceases feeding, attaches itself firmly to some object, and becomes quiet for a time. "The process begins with a splitting of the skin on the upper surface of the thorax: this is continued forward to the head, which opens along the sutures. The head and thorax of the new stage, or instar', are then worked out by an energetic wriggling motion of the insect. and the old skin is gradually stripped off from befors backward, like the finger of a glove. In caterpillars it is known that a fluid, secreted by glands in the hypodermis. is present at molting-times between the new and the old skin, which it helps to separate." (Carpenter.) The caterpillar may be regarded as a recapitu lation of one stage in the phylogenetie develop ment, that is to say. in the evolution of the lepidopterous insect. It may indeed be said to reproduce a stage in the phylogeny of insects best represented to-day by Peripatus, a primitive and widely distributed genus that serves to con nect arthropods with worms.
Pupa tion.—A f ter a ea terpil lar has passed through the period of successive feedings and. moltings which the economy of its species re quires, it prepares to pass into the second larval stage and become a pupa. in which tough integu ments cover the developing organs instead of soft skin. Pupa. may cover themselves with a ease of silk or other materials, called a cocoon, or may remain naked, in which ease they are known as ehrysalhls (sing. chrysalis). The for
mer is the custom among the moths—the latter among the butterflies. The insect in this stage is utterly helpless, and a cocoon serves as a pro tection. It is spun as the last net just before pass ing into the pupal stage. and is formed of silken threads, produced by the hardening of the fluid secreted by the spinning glands. These may be wound round and round the larva until the silken case thus made suffices: or they may form merely the lining of an earthen cell (for ninny pupate under ground), or they may serve to bind into the ei)e0011 own chips of wood. or other materials, or to tie down rolled leaVes, or form a web-like network hung like a bag or a hammock from some support, or making a fuzzy mass in sonic crevice or among leaves and twigs. When the work of spinning the silk is once begun, it is carried on almost without cessation for several days. The forms of cocoons are various; when not concealed, they are usually of a tint that blends well with their surround ings. leaving them inconspicuous, while their ma terial is calculated to resist the attacks of insect eating birds and mammals, or of ichneumon-flies and other intending parasites.
('moons are mainly the work of moths, to which the term 'pupa' is now frequently restricted, for the butterflies pass their pupal stage incased in comparatively rigid integuments, which form a 'chrysalis.' They vary greatly in form. some being acorn-like, others very angular. etc., and most are obscure in tint, so as to be easily over looked. but some are brilliant in color, usually of golden or metallic hues, whence the name chrysalis. Some butterfly chrysal ids ( Nymphal i da-1 are simply suspended from the posterior end (Suspensi) : those of others (Papilionithe) are held in place by an additional strand or gir dle of silk (Succinct i 1. Within the chrysalis or cocoon is the immature butterfly or moth, and all the parts behaiging to the future adult insect may be brood by examination. Breathing goes en through air openings, and the parts steadily develop. "The pupae of the vast majority of moths, of butterflies. and of two-winged flies have the limbs and wings not merely pressed close to the laxly. but immovably fixed thereto by a general hardening and fusion of the outer skin. Such pupa- are distinguished as `obte•t.' But al though the limbs are incapable of motion, certain abdominal segments remain free, so that the hind body call be, to some extent, bent and turned about; and. by means of rows of spines on the abdmninal segments, the pupa is, in many eases, enabled to work its Way out of its shelter, when the time for the final change has arrived." Such are styled 'incomplete.' I'he pupal stage may be of long or short duration. Many Lepi doptera pass the winter or the tropical dry sea son as pure. Some .lave several broods a year, and in such the pupal stage of the hibernating brood will last I ongyr than that of the others.