Larva and Adult of Mediterranean Flour Moth Ephestia Kuhniella Fig 17-Structure of Pupa

Among butterflies, the caterpillars of the tortoiseshells and other species of Vanessa and of fritillaries (fig. 34) are armed with spiny non-poisonous outgrowths of the body and very much the same sort of armature is found in those of the great emperor moths (Saturniidae). In hawk-moth larvae there is usually a single horn near the extremity, while many other caterpillars are entirely smooth (figs. 35 and 36) or only slightly hairy. A very large number of caterpillars protect themselves by feeding only at night; others form cases, webs, or mine into the tissues of leaves, while numerous Tortrices roll leaves into tubular retreats. There are, again, others which obtain a measure of protection by close resemblance to their surroundings. Thus, many geometrid or looper caterpillars bear such a very close resemblance to a mid-rib of a leaf or to a small twig as to render detection a matter of great difficulty. The larvae of some of the hawk moths bear a resemblance to portions of foliage, their diagonal lateral stripes being believed to simulate the effects of light and shade. The caterpillars of the moth Anarta myrtilli, with their intricate green pattern, are hardly discernible among the heather upon which they live. At times the experiments of E. B. Poulton show that the reflection of light from the immediate surroundings produces a nervous response on the part of the caterpillar which results in a physiological change in the accumulation of the pig ment. Thus larvae of the red underwing moth, when subjected to green surroundings, become bluish-green and in a darkly-coloured environment become bluish-grey. Similarly looper caterpillars, if so placed when young, become dark brown among dark twigs and green if placed among leaves.

The Food of

Caterpillars.—Caterpillars, it may be added, feed almost entirely upon the higher plants and there is prob ably not a single family of the latter which does not serve as food for one or more species. Very few are carnivorous and among them are those of some of the Lycaenid butterflies. The caterpillars of the large blue (Ly caena anion), after feeding upon wild thyme, finally enter ants' nests and prey upon the grubs; while those of the North American Feniseca tarquinius feed upon aphides. In the Mediterranean region the larvae of the moth Erastria scitula devour scale insects upon various fruit-trees and are therefore to be looked upon as being beneficial. Certain other caterpillars are cannibalistic, notably those of the common Euro pean moth Calymnia trapezina, but this habit is by no means exclusive and such larvae are also regular devourers of foliage. Some additional instances of unusual feeding habits are given in the section devoted to the economic importance of Lepidoptera.

Silk Production.

The production of silk by caterpillars has already been alluded to ; it is used for several purposes and the best known is for the formation of the cocoon. The latter attains its greatest perfection in those families which include the silk worm moth (Bombycidae) and the emperor moths (Saturniidae): in other cases, as in the tiger moths and tussock moths, the cocoon is much less dense and the silk often intermixed with hairs derived from the larva that formed it.

Sometimes foreign material largely replaces a cocoon and the silk is utilized to draw together leaves to form a pupal shelter (fig. 37) or to cement soil parti cles into a compact earthen cell (fig. 20), as in many hawk moths (Sphingidae) and owlet moths (Noctuidae). Among many but terflies the cocoon is reduced to a slight pad, to which the cremas ter is hooked, and to a mere thread encircling the body of the pupa; in such cases these exposed pupae are protected by their close colour resemblance to their surroundings (fig. 38). Silk is also used by caterpillars as a "life-line" which is run out through the spinneret as quickly as it is secreted, and by means of this device such creatures elude their enemies or save themselves when blown off or shaken from their food-plants, by remaining suspended by the thread until the danger has passed. Other caterpillars, when young, are gregarious and secrete guiding threads over their f ood plant, which enable them to maintain their foothold; others go a stage further and construct communal webs, within which they feed, gradually dispersing and becoming solitary as they grow older.

The Chrysalis.

The pupa or chrysalis in the majority of Lepidoptera is of the obtected type with the appendages glued down to the body, which presents a hard compact appearance in consequence (fig. 36). Such pupae have little or no power of movement of the abdominal segments and remain in a fixed posi tion, being attached by the cremaster (fig. 36) to the cocoon, or to a silken pad in the case of many butterflies. The cremaster consists of a group of hooks or a prominent spine at the caudal extremity of the body and is formed from the last dorsal shield, overlying the vent in the larva. Obtected pupae are found in all the higher groups, from the Lasiocampoidea to the butter flies. Among the lower groups, the pupae are termed incomplete; they have the appendages partially free from the body, instead of being soldered down, and the abdomen has several of the seg ments freely movable. The latter feature, aided by girdles of spines, enables such pupae to work their way out of the cocoons or burrows and come to the face to allow of the exit of the perfect insect. Except in the Pterophoroidea the cremaster is absent or but little developed. In the Micropterygidae the pu pae closely resemble those of the caddis flies (Trichoptera) and are of the free type, with all the abdominal segments movable and the appendages entirely free from any secondary attachment to the body. Functional mandibles are present which enable these pupae to bite their way through the co coons when the time for eclosion of the moths approaches. In some cases special devices are present in order to enable the moths to effect their emergence. In the puss moth (Dicranura vinula) the insect secretes potassium hydroxide as a solvent which softens the hard woody walls of the cocoon ; in the emperor moth (Saturnia pavonia-minor) , the arrangement of the silk at the front end of the cocoon expressly allows of the free egress of the insect ; while cer tain other moths are provided with temporary spines or plates which function as cocoon cutters in the same way as the girdle of spines mentioned above.