The butterfly guide

by W. J. Holland

THE LIFE HISTORY OF BUTTERFLIES

Almost all insects undergo great changes, or metamorphoses, during their existence. Butterflies furnish no exception to this statement. They exist first as eggs; then they appear as caterpillars; the third stage is that of the chrysalis; the final stage is that of the imago, or perfectly developed insect.

THE EGGS OF BUTTERFLIES

The eggs of butterflies are beautiful objects when examined under a glass. They have various forms. Some are spheres or half spheres, some are conical, cylindrical or spindle-shaped, others are flat and resemble little cheeses, and still others have the form of turbans. There is endless variety of form displayed within certain limits. Their surfaces may be quite smooth or they may be adorned with raised ribs and sculpturings (see [Plate C], Figs. f and g) or marked with little pittings or depressions arranged in geometrical patterns. They vary in color. Some are white, some pale green, or blue-green; others are yellow, orange, red, or purple. They are often spotted and marbled like the eggs of some birds.

The eggs of butterflies are deposited by the female upon the plants which are appropriate to the development of the larvæ. Caterpillars are very rarely promiscuous feeders, and most species are restricted to certain species or genera of plants. Even when they feed upon different plants, observation shows that, having begun to feed upon a certain plant, they prefer this to all others, and do not willingly accept anything else. I have noticed frequently that larvæ which may for instance feed in nature upon the wild plum or the lilac, having begun to feed upon the one will steadily refuse the other if offered to them. On several occasions I have lost broods of caterpillars by attempting to change their diet, though knowing well that the species is found feeding in nature upon the plants which I have offered to them. Almost every plant has a butterfly or moth which is partial to it, and one of the most wonderful things in nature is the way in which the female butterfly, without having received a botanical education, is able to select the plant which will best meet the needs of her progeny, which she never lives to see.

The eggs are deposited sometimes singly, sometimes in small clusters, sometimes in a mass. Fertile eggs, soon after they have been laid, undergo a change in color, and it is then possible with a magnifying glass to see through the thin shell the form of the caterpillar which is being developed within.

When the development is completed the caterpillar emerges either from an opening at the side or at the top of the egg. Many species have eggs provided with a sort of lid, a portion of the shell being separated from the remainder by a thin section, which finally breaks under the pressure of the enlarging embryo within, this portion flying off, the rest adhering to the twig or leaf upon which it has been placed. Many larvæ have the habit, as soon as they have emerged from the egg, of making their first meal upon the shell from which they have just escaped.

CATERPILLARS

The second stage in which the insects we are studying exist is known as the larval stage. When it is reached the insect is spoken of as a larva, or caterpillar (see [Plate C], Fig. h). Caterpillars have long, worm-like bodies, which are often thickest about the middle, tapering before and behind, and more or less flattened on the under side. Sometimes caterpillars are oval or slug-shaped. Very frequently their bodies are adorned with hairs, spines, and tubercles of various forms. The body of the larva, like the body of the butterfly, consists normally of thirteen rings or segments, of which the three foremost, just behind the head, correspond to the prothorax, the mesothorax, and the metathorax of the perfect insect, while the remaining nine correspond to the abdomen of the imago. These three anterior segments bear legs, which correspond to the legs of the winged form in their location, and are known as the true legs of the larva. Besides these the caterpillar has about the middle of the body and at its posterior end paired pro-legs, as they are called, which are its principal organs of locomotion in this stage, but which do not reappear in the butterfly. The mouth parts of caterpillars are profoundly different from those of the butterfly. The imago lives, as we have seen, upon fluid nourishment, and therefore is provided with a sucking organ, the proboscis. The caterpillar, on the other hand, is armed with a pair of cutting mandibles, with which it shears off tiny strips of the leaves upon which it feeds. It holds the edge of the leaf in place with the three pairs of true legs, while it supports its body upon the pro-legs during the act of eating.

EXPLANATION OF PLATE C

Fig. a.	Caterpillar of Anosia plexippus ready to change into a chrysalis.
Fig. b.	Do. after having partly shed its skin.
Fig. c.	Do. holding itself suspended in the air by grasping the shed skin between the edges of the third and fourth abdominal segments, and feeling about with the cremaster for the button of silk above.
Fig. d.	Do. after having caught the button and assumed its final form as a chrysalis.
Fig. e.	Chrysalis of Papilio philenor, held by button and girdle of silk.
Fig. f.	Egg of Basilarchia disippus, greatly magnified.
Fig. g.	Egg of Anosia plexippus, greatly magnified.
Fig. h.	Caterpillar of Basilarchia disippus.
	(All the figures are after Riley.)

Plate C

When the caterpillar emerges from the egg the head is in many cases seen to be very large in proportion to the rest of the body. This relative disparity soon disappears, however, as growth takes place. As the larva increases in size, it soon reaches a point at which the skin in which it made its appearance in the world becomes too small and tight for further comfort and use. Thereupon it proceeds to moult, or shed, this now uncomfortable garment. The skin splits along the back and the caterpillar crawls out of it. Before moulting the caterpillar always takes the precaution to attach this outer skin by strands of silk to the leaf or branch upon which the moult is to take place. Having escaped from the cast-off garment, the caterpillar sometimes turns around and eats it before resuming its vegetable diet. The process of moulting takes place four or five times before the larva changes into a chrysalis.

Caterpillars differ entirely from butterflies in that they are able to produce silk. Silk is a viscous fluid secreted by elongated sacs located in the dorsal region. These sacs communicate with a minute tube-like organ, known as the spinneret, which is located on the under side of the head of the caterpillar, just back of the mandibles. The fluid silk, as it is ejected through the spinneret, immediately hardens on contact with the air and is deposited in the form of very fine threads or filaments which the caterpillar uses for various purposes, sometimes as lines with which to guide itself from place to place and enable it to retrace its steps to its favorite resting-place, sometimes to tie together the leaves in which it forms its nest, or to weave a sort of shelter in which it conceals itself, and finally to make the little buttons and the girdles by which, as we shall see later, the chrysalis is held in place. Many moths weave from silk compact structures known as cocoons, in which the chrysalis is lodged. Butterflies do not weave true cocoons.

The time spent by the insect in the egg is generally short. The time passed in the larval state may be short or long. When butterflies hibernate, or pass the winter, as caterpillars, the time spent in this state is long, and especially in the case of those species which inhabit arctic regions. There are some butterflies which occur north of the Arctic Circle, and we have ascertained that these, because the summers are so short in the far north, pass two summers and the intervening winter in the larval condition, and another winter in the pupal stage, before they emerge and take wing. On the other hand, under more temperate conditions butterflies of certain species may produce two or even three broods in a summer, and in subtropical or tropical lands there may be even more broods produced.

While it is true that almost all the larvæ of lepidoptera subsist upon vegetable food, there are nevertheless exceptions, one of which is that of the Harvester, Feniseca tarquinius (see [Plate LXXXVIII], Fig. 1), the slug-like larva of which feeds upon scale-insects, or mealy bugs, sharing the habit with certain allied species which occur in Africa and Asia, as the writer has had occasion to point out a number of years ago in certain of his writings.

THE PUPA, OR CHRYSALIS

The third stage in the life of lepidoptera is known as the pupal stage. The caterpillar, having undergone successive moults and reached maturity, is transformed into a pupa, or chrysalis (see [Plate C], Figs. d and e). From having been an active, worm-like creature, greedily feeding upon its appropriate food, it reverts to a form which is stationary, as was the egg, and ceases to have the power of locomotion. An examination of the structure of all chrysalids shows that they contain an immature butterfly. The segments of the chrysalids enclose the corresponding segments of the body of the butterfly, and in sheathing plates of chitinous matter are enfolded the wings and all the other organs which are necessary to the life of the butterfly when it shall have emerged and taken wing. The act of transformation from the caterpillar stage to the pupal stage is very wonderful. The caterpillar makes provision for the great change by weaving a little button of silk and, in the case of many of those larvæ, the chrysalids of which are not pendant, by also weaving a little girdle of silk, which it passes around its back, and which holds it in place very much as an Indian baby is held by the strap which passes over the shoulders of the squaw (see [Plate C], Fig. e). Having made these preliminary arrangements the caterpillar becomes very quiet, its hind pro-legs being securely hooked and tangled into the silken button to which it is attached. After a while, when the proper moment has arrived, the skin of the caterpillar splits, just as in the moults which preceded, and by a series of wriggling or vibratory motions the chrysalis succeeds in working off the skin of the caterpillar until it has all been shed except where near the end of the abdomen the skin is caught between the edges of two of the horny rings which form the abdomen. Then the insect with the cremaster, as it is called, a little spikelet at the very tip of the chrysalis, which is armed with small hooks, proceeds to feel about until these hooks become entangled in the silk of the button which has been provided on the under surface of the twig, the stone, or the fence rail, where the transformation is occurring. As soon as the chrysalis is securely hooked into the button of silk it lets go of the little section of the skin by which it has been supported and rapidly assumes the shape in which it will remain until the time of its emergence as a butterfly. These changes are illustrated on [Plate C], Figs. a-d, which are reproduced from “The Butterfly Book” after the drawings of the late Prof. C. V. Riley. The chrysalids of all the Nymphalidæ are pendant; those of the other families, except the Hesperiidæ, are provided with girdles, as is shown on [Plate C], in the figures which represent the chrysalis of Papilio philenor. The chrysalids of the Hesperiidæ, like the chrysalids of moths, are either formed in loosely woven coverings of leaves tacked together with silken threads, or lie free under leaves and rubbish upon the ground, thus resembling the chrysalids of moths.

Chrysalids are for the most part rather obscure in coloring, though some are quite brilliantly marked with metallic spots as in the case of the common Milkweed Butterfly, Anosia plexippus, the chrysalis of which is pearly green in color, ornamented with bright golden spots.

The forms assumed by chrysalids are very various, especially among the Nymphalidæ, and they are often ornamented with curious projections and tubercles, imparting to them very odd outlines.

Some butterflies remain in the chrysalis stage for only a few days or weeks; others pass the winter in this state, and this is true of many of the species which are found in the colder parts of North America. In temperate regions some butterflies have as many as three broods: the spring brood, which comes forth from chrysalids which have over-wintered, an early summer brood, and a fall brood. In tropical countries many species retain the form of the chrysalis during the dry season, and emerge upon the wing at the beginning of the rainy season, when vegetation is refreshed and new and tender growths take place in the forests.

THE IMAGO, OR WINGED INSECT

We have already spoken at length of the form and structure of butterflies in the preceding paragraphs, which were devoted to the anatomy of butterflies. It remains for us at this point to call attention to the manner in which the butterfly undergoes transformation from the chrysalis. This change is quite as interesting as that which takes place when the caterpillar is transformed into the pupa; and should any of my readers possess chrysalids I would advise them to watch carefully and observe the curious events which follow one another rapidly when the imago comes forth from the cerements of the chrysalis. The coverings which ensheathe the head, the legs, and the antennæ split, the head protrudes, the fore legs are disentangled and are thrown forth, followed almost at once by the other legs, and the insect proceeds to crawl out from the pupal skin, emerging with the wings as miniature objects, the body trailing after as a long worm-like mass. Having liberated itself from the sheathings of the chrysalis, the insect immediately assumes a stationary position, head upward, body hanging downward. Then by the action of the heart the fluids which fill the body begin to be rapidly sent into circulation, more particularly into the wings, which expand second after second, minute after minute, the fluids in the body being transferred through the circulatory system of the wings until the latter, hanging downward, have assumed their full form. The insect then begins gently to move its wings, to fan them, still remaining in the position which it first took. After a while the wings become perfectly dry, and the long worm-like body has shrunk up and has assumed the form which it will retain through the subsequent life of the insect. Madame Butterfly then begins to change her position. She carefully crawls a few steps to try her powers of locomotion. She suddenly expands her wings, and, presto! if you alarm her, she is off, fluttering about the cage in which you may have her, or darting forth into the room and through the open window, hieing herself forth in quest of food, which awaits her in the honeyed cups of the wild flowers.

EXPLANATION OF PLATE D

Fig. 1.	Illustration showing the way to disable a butterfly in the net by gently pinching the body where the wings come together.
Fig. 2.	A butterfly net.
Fig. 3.	a, hoop made of wire, the shanks tied together; b, ferrule, plugged at c with a piece of cork; the shanks having been put into the top of the ferrule, melted solder is poured into the top, and a good net-ring is made.
Fig. 4.	Piece of paper used to cover cyanide at bottom of jar.
Fig. 5.	Collecting jar, with lumps of cyanide and sawdust at bottom, covered by paper, as shown in Fig. 4.
Fig. 6.	Expanding block, used to expand and mount insects, the wings of which have a tendency to droop or sink down.
Fig. 7.	Expanding block, used to mount insects, the wings of which have a tendency to rise up or close.

Plate D