Page:The New International Encyclopædia 1st ed. v. 03.djvu/831

* BUTTERFLIES. 735 BUTTERFLIES. foes, they would soon destroy the vegetable king- dom. They injure, or even kill, shrubs and trees, as well as all sorts of jrarden vejidables. They eat woolen stutFs of all kinds and furs. To offset all their destruotiveness, they ofl'er 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 Lycaenidse, which feed on phint-lice and scale-insects. One such species (Feniseca I'arquinius) occurs in the United States. A few forms are aquatic and feed on plants under water. Self-I'rotcction in Cdtcrpillars. — The skin of some caterpillars is naked, that of others is cov- ered with hairs, spines, or tubercles, ilost are solitary, but some make for themselves nests or tents of silk, under ^hich they dwell in societies, j)rotected 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 li.x 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, ilost 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 eft'ort 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 u-seful 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 ma' 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, liungry 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 be said elsewhere. Others, such as the geometrids or measuring worms, may coml)ine with this pro- tective eohiration the capacity of attaching them- selves 1)3' the liind end and stretching out in the air like a twig. This rigid attitude thej' 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 folds, and marks on the anterior end give some forms the appearance of snakes or other strong animals. The color of caterpillars is due to two sources: (1) Pigment gained from the food: (2) pigment inherent in the deep-lying tissues or .s^in. Most green caterpillars seem in some way to be col- ored by the chlorophyll of the food-plant. Yel- low is derived mainly from .;intliophyll of plants. Pigment derived from food-plants tends gradually to give the caterpillar the coloration of the surroundings. See Protective Colora- TIOX ; illMlCRY; etc. iilruyyie for Existence. — Only a few out of the vast hosts of caterpillars ever reach maturity. Many are destroyed by cold, wet, droutli, 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 Hies deposit their eggs within great num- bers of caterpillars, where they develop and eventually kill the caterpillar or pupa. Tachina- llies also lay their eggs on caterpillars and the larv;e 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. — Soon 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 unelastic, and must be shed. A number of such moltings or eedyses take place before the embryo attains full size. These normally occur at regular intervals, and four or live 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 egg 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 before backward., like the finger of a glove. In caterpillars it is known that a fluid, secreted by glands in the hy[)odermis, 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 phylogenetic develop- ment, that is to say, in the evolution of the lepidopterous insect. It may indeed be said to leproduce a stage in the i)hylogeny of insect.s best represented to-day by Peripatus, a primitive and w-idely distributed genus that serves to con- nect arthropods with worms. Pupation. — After a caterpillar 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 lar-al stage and becofue a pupn, in which tough integu- ments cover the developing organs instead of soft skin. Pupae may cover themselves with a> case of silk or other materials, called a cocoon, or may remain naked, in which ease they are known as chrj-.salids (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- lection. It is spun :is the last act 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