Part 4

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.)

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.

COLLECTING BUTTERFLIES

In collecting butterflies the first thing is to get a net of some kind with which to catch the insects without tearing their delicate wings, and thus robbing them of their beauty (see Plate D, Figs. 1 and 2). When I was a boy I made my own nets. I took a stick of tough wood about four feet long, which was to serve as the handle. About seven or eight inches from the upper end I wrapped it with copper wire; fishing line will do as well. Then I split the stick down to the band I had made around it. I then with my knife trimmed the two split portions on their inner sides, so that they might be more flexible. I then fashioned out of a piece of good green hickory (the white outer wood must be used) a bow or hoop about twelve inches wide at its widest part, and fitting this between the split ends of the stick put in a wedge at the bottom of the cleft to keep the split ends well apart and tied it neatly and securely in place. Upon the frame made in this way I put a covering of green mosquito netting in the form of a long bag. Many a fine insect I captured with this simple device, which called only for a good jack-knife, a little ingenuity, ordinary skill in whittling, and a supply of stout string. The cheapest and simplest way to make the frame for a net is to take a long piece of brass, aluminium, or galvanized iron wire about an eighth of an inch in diameter and bend it into a circle, leaving two short shanks at the end. Then fit the shanks into the top of the ferrule of a fishing-rod plugged in the middle with a thin piece of cork or with clay, and pour in melted solder. Plate D, Fig. 3 shows how the “trick” is done.

There are many devices for making frames for folding nets, and there are a number of dealers in the United States who supply such nets at moderate prices. The material for the bag of the net ought to be of light stuff, and I prefer to use tarletan, preferably green in color, or bobbinet. The latter is more durable though somewhat heavier than tarletan. The bag of the net ought to be about three times as long as the diameter of the ring upon which it is placed. It is well, after the net has been sewed upon the ring, to cover it with a band of stout dark-colored muslin, as otherwise the edge of the bag surrounding the ring is apt to become speedily worn and torn.

The collector having provided himself with a net for capturing insects must also provide himself with one or more collecting jars. It is well to have several of these of a size convenient for carrying in the pockets. For large specimens a larger jar is required; for small specimens a smaller receptacle is better. The larger jar should have the mouth about two and one half or three inches in diameter. Wide-mouthed glass phials an inch and a half in diameter serve best for the smaller receptacles. The stopper of the larger jar should be of ground glass, of the smaller jar of good cork. Jelly tumblers or glasses with tin tops make good collecting jars. In preparing the jar for use place a few lumps of cyanide of potash about the size of a filbert at the bottom; then put in a little clean sawdust to keep the pieces of cyanide from rattling about; over the lumps of cyanide paste a sheet of strong white paper perforated with a multitude of holes. In doing this the writer has resorted to a simple method, which is explained in the diagram on Plate D, Fig. 4. A piece of paper is placed under the jar and a circle the size of the inside of the jar is traced upon it. Then a disk is cut out about three quarters of an inch greater in diameter than the original circle. The paper is punctured over the entire surface included within the inner line, and then with scissors little gashes are made from the outer circumference inward, so as to permit of folding the edge of the disk inwardly. A little gum tragacanth, or paste, is then applied to these upturned edges, the disk is then inserted into the jar and pasted securely over the cyanide by means of the upturned flaps. A jar thus charged will last for a long time if kept stoppered when not in use. Cyanide has a tendency to liquefy in the presence of moisture, and it is well therefore to take care to keep the jar closed when not in use. It must, however, be borne in mind that the fumes of hydrocyanic acid (prussic acid), which are active in producing the death of the insect, will not be given off in sufficient volume unless there is a small amount of moisture in the jar, and in very dry climates the writer has sometimes found it necessary to moisten the bottom of the jar with a drop or two of water. Jars also may be charged with lumps of carbonate of ammonia, but as this substance bleaches the wings of insects, especially those which are green in color, its use is not strongly recommended. Figure 5 on Plate D shows a jar prepared for use.

When a butterfly has been caught in the net it is apt to flutter about and struggle violently, thus injuring its wings. It is well therefore as soon as the insect has been captured to take hold of it at the point where the wings join the body, while it is still in the net, and by gently pinching the thorax to disable the insect. The fingers are applied from the outside, as shown in the illustration (see Plate D, Fig. 1). Then the collector, unstoppering his jar, inserts it into the net and allows the butterfly to drop into the jar. Butterflies belonging to the family of the Hesperiidæ, or “skippers,” are best captured in the net by holding up the end of the bag. The insects will then fly upward and settle near the top of the bag. The collector puts the open jar with his right hand into the ring of the net and holding the bag with the left hand brings the jar under the butterfly, and then claps his left hand over the mouth of the jar, thus securing the insect in the jar, where after a couple of seconds it will be stunned by the fumes and fall to the bottom. Death is speedy, but not instantaneous, and the insect should be allowed to remain a little while in the jar. Having been asphyxiated by the fumes of the jar, the insect may then be removed and either mounted upon a pin and transferred to a collecting box, which will presently be described, or put into an envelope. It is well not to accumulate too many insects in the collecting jar, as those which are caught later will injure in their struggles those which have been caught first. I make it a rule to rapidly transfer the insects from the collecting jars to the collecting boxes which I carry with me. The preservation of specimens in perfect freshness, without torn or ragged wings, is of the utmost importance, and it is better to take fewer specimens, preserving them in immaculate condition, than to accumulate a quantity of ragged and battered examples. The old adage, “Practice makes perfect,” applies in the use of the net and the poisoning jar. There will necessarily be some failures on the part of the young collector at the outset, but if he is neat and quick of finger he will soon acquire the art of taking and preserving perfect specimens.