In the study of Natural History it is the habits and life-histories of the living animals which appeal most strongly to young people. A large part of the leading Botanists and Zoologists of this country began, as young people, their studies of Nature by collecting animals and plants and studying their life-history and habits. It is this dynamical side, the relation of the animal to its surroundings, which arouses our interest. Since this has been the most natural method by which the interest in nature has been developed, it is surprising how little this side of Zoology has been encouraged by many of our better colleges and universities.

From the standpoint of the teacher, insects as a rule, stand very high with regard to the interest which they arouse in scholars for nature-study. This is quite natural, since the great abundance and interesting habits of these animals make them comparatively easy to study.

The two insects which we figure this month are very common and widely distributed, and thus have become very generally known. When we once become familiar with them, these beautiful moths are of perennial interest, and each season one is pleased to renew his acquaintance with them.

The Cecropia is our largest and to many persons the best-known moth. Its gigantic size, varying from about 4 to 7 inches in expanse of wings, together with its bright colors, makes it an easily remembered insect. The scientific name of this moth (Samia cecropia) is the first scientific name of an insect that many of us can recall learning. The time of active flight is at night, and thus it is that they are so frequently found in numbers about electric lights to which they have been attracted by the intense light. Their rather awkward flight and large size often lead to their being mistaken for bats.

The differences between the sexes are not so manifest as in Promethea, yet it is not difficult to distinguish them. The females are larger and have stouter bodies, but the most conspicuous difference is that the "feelers" or antennae of the male are feather-like and very large and broad, while those of the female are only about one-half as broad.

The eggs are somewhat flattened, about one-tenth of an inch long, pale in color, and are deposited by the female in small patches upon a large variety of plants, since there are about fifty of these upon which the larvae will feed. The eggs usually hatch in about a week or ten days, the young larvae being very different in appearance from the mature ones. The changes in appearance are brought about by five moults or sheddings of the skin. The full-grown larva is pale green or light blue, 3 or 4 inches long, armed with eight more or less complete rows of large tubercles. Those above on the second or third thoracic segment, are bright red; all the others are yellow except those on the sides of the body and on the first thoracic and last body segment, which are blue. Unfortunately, these colors soon fade in the dead larva as is seen in the plate. This wonderful development of tubercles seems to be in some way related to the arboreal habits of the larvae.

Although a variety of parasites which prey upon these larvae is not large, they are very numerous in individuals, and it is to this cause that only a small per cent of the larvae ever produce moths. These parasites develop beneath the skin of the larva as footless grubs, which, at first, do not attack the vital organs, but later these organs are preyed upon, and the larva dies. A wasp-like insect which preys upon this larva well illustrates in its habits the crudeness of many instincts. The female will lay eight or ten eggs upon one caterpillar, but as the young parasitic grubs require a large amount of food, only one is able to mature and the others perish.

The insect parasites seem, in many cases, to mature and transform into the adult stage after the caterpillar has built its cocoon, and thus many parasites lose their lives, since they are not always able to escape from the cocoon. A cocoon will sometimes be found filled with these small insects, which have not been able to make their escape, and have thus died in prison.

The adult larva, unlike Prometha, usually spins its cocoon not attached to a leaf, but along a stem; sometimes, however, they may be placed in other situations.

In about two weeks after the cocoon has been spun, the larva transforms into a chrysalis, in which stage it hibernates during the winter, and from which it emerges in May or June.

During the winter, when the leaves are not on the trees and shrubs which are frequented by these larvae, a large number of cocoons may easily be collected. These should be kept out of doors during the winter, for if kept in a warm room they will emerge during the winter or so early in the spring that food cannot be secured for the larvae.

If one secure a number of old cocoons, from which the moths have failed to emerge, and cut them open longitudinally, he may learn many interesting facts. A dead and dry mummified looking larva or chrysalis may be found, or, what is even more interesting, no trace of the larva or chrysalis may be present, but only a mass of small white, paper-like cocoons. These have been left by a colony of little wasp-like parasites which may occur in such large numbers that there is scarcely room for all to spin their cocoons, so that on account of being so closely crowded together, they are moulded into a mass of cocoons having the form of the cavity formerly occupied by the larva.

The cocoons of Cecropia are composed of two parchment-like layers of silk which are generally very dense and strong. The space between these two layers contains loosely spun threads of silk like a layer of packing material. The larvae seem normally to make three varieties of cocoons; one kind is very loosely constructed, much larger than the ordinary form and not attached to a twig, but found in the grass or in shrubs near the ground. The two other forms of cocoons are much smaller and more closely woven, but differ in size; female moths as a rule emerging from the larger cocoons, and males from the smaller ones.

Dead larvae are sometimes found in cocoons which are practically of a single thickness; there being no space between the outer and inner layers. The hollow skins of the larvae found in such cocoons clearly show that this unusual cocoon is due to the influence of parasites upon the larva.

In the upper open end of the cocoon, kernels of wheat, corn, beechnuts and even acorns have been found. How these get in this position seems to be quite a puzzle. In opening twenty or thirty cocoons, five or six kernels of corn have been found, thus showing that this occurrence is by no means rare. Chickadees and blue-jays have been given the blame for this work, since these birds are thought to have the habit of hiding food. The inverted outer layer of the cocoon clearly shows, in some cases, that the kernel of corn has been thrust into the cocoon with some force.

The head of the pupa lies at the small end of the cocoon, where the texture is less dense, and thus, when it is ready to transform into the moth, the head is in the best position for easy escape from the cocoon. But this provision alone is not sufficient to make sure the escape. At the time of emergence, the pupa secretes a fluid which escapes from the mouth and by moistening the cocoon softens the glue-like material which binds together the threads, thus making it possible for the freshly emerging moth to crowd its way between the fibres, and thus secure its freedom. When the moth first crawls out of the cocoon, its heavy body and small folded wings show but little resemblance to the fully-expanded moth. By degrees, however, the wings expand and become more rigid, the colors brighten, and finally the mature moth is developed.

The Promethea Moth is only about one-half the size of Cecropia, and the two sexes are very different in appearance; so much so that one would not at all think they were the same kind of moths. As in Cecropia the male moths are somewhat smaller than the females, and the antennae show the same kind of differences, i.e., the antennae of the males are much larger and feather-like. In color, the sexes of Cecropia are much alike, but in this moth the differences in color are very great, the dominant color in the female being a reddish brown, while that in the male is a very dark-brown or almost black. Thus these moths furnish an excellent illustration of what is called sexual dimorphism, a term used for those animals in which the sexes are very different in appearance, a subject to which Charles Darwin gave considerable attention, in his "Descent of Man."

The female moth lays her cream-colored eggs, which are a little smaller than those of Cecropia, upon shrubs and trees in clusters of five or six. The small larva usually hatches in about ten days, and feeds upon the leaves of ash, sassafras, lilac, tulip tree, maple, cherry, and a number of other trees and shrubs, but it is much more select in the choice of its food than Cecropia. The larvae have voracious appetites, devour many leaves and grow at a correspondingly rapid rate. The differences between the very young and the adult larva, aside from that of size, are very great. On account of the very limited elasticity of the skin, this larva, like other insect larvae, only increases in size after shedding. This is periodically accomplished by throwing off the old skin, which prevented expansion, and by growing a new and larger one. Promethea has from three to five of these moults, the number being influenced apparently by climate, since southern larvae have more moults than northern ones. The time between these moults varies from two days to a week.

The leaves upon which the larvae feed may have long or short petioles. A singular account has been given of how these larvae have overcome the difficulties associated with feeding upon long-petioled leaves. There is considerable risk of falling and of the leaf breaking away when a large larva crawls out upon a slender petiole. The larva avoids these risks and yet reaches the blade of the leaf. This is accomplished as follows: The larva grasps firmly the branch with its posterior legs; reaches out a considerable distance along the petiole, and bites it through in several places. This causes the leaf to droop; the larva now reaches out, seizes the drooping leaf, and draws it within convenient reach, where it can be eaten at leisure. This is a wonderful display of instinct, yet it is not infallible, because at times the petioles are eaten too far through, and when they droop, break completely away and fall to the ground.

When ready to spin its cocoon, the adult larva is about two inches long; these cocoons are very different from those of Cecropia. As a rule, they are found suspended from a branch by a silken cord, the length of which depends upon the length of the petiole of the leaf in which the cocoon was spun. Thus if the leaf has only a short petiole, this cord is also short, but if the petiole is two or three inches long, the suspensory cord is correspondingly long. The larva in constructing its cocoon, first spins a strong band around a twig, and binds the petiole of the leaf to the stem; this band extends down the petiole to the cocoon, and thus anchors it. The cocoon proper, or the part occupied by the chrysalis, is spun in a folded leaf. When this leaf dies and rots away, the cocoon hangs freely suspended by the cord, but it is very evident that the cocoon has been moulded in a leaf by the prints of the veins which remain upon it. A valve-like opening occurs in the upper end, through which the moth emerges.

The wings of the chrysalis are very small as compared with those of the adult moth; are folded to the body on the under side, and covered by the pupal skin. During the winter they remain transparent since there are at this time none of the rich colors present which are later found in the moth. About ten days before the moth emerges the wings become white, a few days later definite colors begin to appear on the under side of the wings between the veins. While in the adult moths the colors in the two sexes are very distinct, at this time their wings are very similar. The wings do not long retain this similarity, but gradually become more and more unlike until maturity.

Breeders of moths have often noticed that there is considerable uniformity with regard to the time of day at which certain kinds of moths emerge. For Promethea this time seems to be in the forenoon.

From an extensive series of experiments, it has been learned that the male finds his mate by means of scent and that this is doubtless the explanation for the very large antennae of the male, since it is in these organs that the sense of smell is located.

Although it may be very interesting to read about the activities of insects, a much more fascinating side of the subject is to handle and study the insects themselves, and there are but few better insects with which to begin a personal acquaintance than these which we have been considering.

Charles Christopher Adams.