British Butterflies

CHAPTER I. The Life-History of a Butterfly

THE LIFE-HISTORY OF A BUTTERFLY

What is the difference between a butterfly and a moth, and how am I to distinguish between them? is a question very often put to the student of insect life--the entomologist.

Butterflies and moths both belong to the Natural Order, Lepidoptera, or scale-winged insects. Butterflies may be distinguished as day flyers, and the moths fly by night. The main physical difference between them appears in the forms of the antennæ, or horns; in the butterflies these organs are club-shaped at the extreme ends. But the antennæ of the various species do not all follow a common pattern. In some the knob is abrupt and much smaller, after the manner of a drum-stick; in others, the thickening commences well down the shaft, and is gradually increased until it very much resembles an Indian club. The antennæ of the moths, on the other hand, show much diversity of form, and in a great many species they are totally different in the male and female. A very common and beautiful form is the feathered, or comblike, antenna; another is long and threadlike, and some show a combination of these two forms; others, again, seem to be striving after the butterfly type, and approach the club shape. It should be noted that not a few moths fly during the day, but it is rare, exceedingly rare, to find a butterfly abroad after sundown. With a little practice in observation, the novice soon learns to distinguish between the two.

The stages of development of butterflies and moths are practically the same: first the egg; next the caterpillar, or larva; then the pupa, or chrysalis; and, lastly, the imago, or perfect insect.

The eggs of the Lepidoptera are surpassingly beautiful. Are they like birds' eggs? Not at all! In the first place they are too minute for comparison with the larger product of the birds; both in colour and form they more nearly resemble small shells or pearls, as a great many of them are beautifully opalescent, especially when empty. A good hand-lens will reveal a great deal of their beauty, but the low power of an ordinary compound microscope will be necessary to enable you to see all the nice detail of pattern sculptured on their surfaces. Each species of butterfly, or moth, produces eggs of particular shape and ornamentation, so it is quite possible, in most cases, to say to which species an egg belongs. How long the egg may remain unhatched depends a good deal upon which butterfly's egg it is, the season of the year, and the temperature. Not many butterflies pass the winter in this country in the egg state, that season being usually passed either as a half-fed hibernating caterpillar, or as a chrysalis; and in a few cases it is only the female which passes the winter in some secure retreat, to emerge again in the spring, and then deposit her eggs on the fresh-growing verdure. But, generally speaking, eggs laid during the summer hatch out in from ten to sixteen days. And it is well to be on the lookout for the young larvæ even earlier, if you intend to rear some species in confinement. If you have secured eggs to rear from, watch them from day to day to see if they darken, as they often assume a dark leaden hue immediately before hatching. This is a useful warning, and serves as a hint to have plenty of fresh food ready for the young family about to arrive.

The caterpillars are ravenous eaters; you will not notice this fact particularly at first, because they are then such tiny creatures, but in proportion to their size their eating capacity is enormous. They grow at an exceedingly rapid rate and to such an extent that they literally burst their skins! In a very short time--three or four days--the old skin bursts and out comes Mr. Caterpillar with a brand-new one. And this is the manner of their growth; several times (five or six) this skin-shedding process is repeated. And then the creature prepares for the last and final change before turning into a butterfly.

There are one or two more points I would ask you to notice about our caterpillar ere we pass on to consider his next stage. The legs are generally sixteen in number. There are six true legs, one pair on each of the first three body-segments behind the head; four more pairs near the anal end, and the last segment carries another pair, known as the "anal claspers." The first six may be said to represent the same legs in the perfect insect. Note also the breathing holes, or spiracles, placed in a row along either side of the larva. The head seems to carry very large eyes, but it does not really do so; the real eyes are very minute, and it requires a good strong pocket-lens to make them out. There are twelve of them all told, and they are not all of equal size. There are six on either side of the mouth, and the three larger ones on each side are not very difficult to find. The mouth is furnished with strong mandibles for biting and chewing food, and also contains the spinneret for the production of the silk used on various occasions. All these details should be carefully noted--the head, the eyes, the breathing spiracles, the mandibles, the fore-legs and claws, and the hind- or pro-legs. Mark the totally different types of feet which terminate these two sets of legs. You will need to use your lens for this observation, and to enable you to see the beautiful structure of the pro-leg foot, it will be necessary for you to examine it through a compound microscope. It is well for the young entomologist to know these more prominent features of a caterpillar's economy, if for no other reason than to be able to answer the questions that are sure to be put to him on these and many other points.

But only a small percentage of the larvæ that are born into the world live to become butterflies; some seasons a larger number than usual may escape, and then we have a butterfly year, but the relentless ichneumon flies soon restore the balance. They, too, have their young to provide for, and a strange mode of existence they have. Once you get to know these ichneumons at sight, you will be astonished at the number of them. All the summer through you will find them hawking about the trees, bushes, nettles, and heather, and, indeed, wherever larvæ are to be found, there, too, you will find these flies. There are many species of them. Once a female has discovered a larva its doom is sealed. The ordinary larva has very few defensive weapons; he may wriggle and squirm and look terrifying, but all the same the ichneumon sets about her task of placing one or two, and in many cases a dozen or two, of her eggs either upon or under his skin. These eggs soon hatch, and the little white maggots pass their existence inside the doomed creature, eating all the tissues away, at first avoiding the vital organs, which they leave until the last. When they have reached their allotted span, and are about to change to the pupa state themselves, they soon finish off their victim, and all that remains of what might have been a brilliant butterfly is a little shrivelled bit of skin and a host of little--or it may be a few big--black, brown, or grey flies. Sentiment apart, these parasitic flies are extremely useful. When you consider the large number of eggs laid by a single female butterfly or moth--from two to six hundred is a fair average--you will realize that if this enormous progeny were to survive and go on increasing without any check, the vegetation of the world would very soon prove quite inadequate to support the vast army of caterpillars, to say nothing of you and me.

You may at some time find a dozen or two larvæ of some particular species of butterfly or moth, and at the time of collecting them they may seem healthy and all right, but weeks afterwards you may discover that only a very small number will change to chrysalids, the ichneumons having had the rest. If you can catch and induce a female butterfly to give you a batch of eggs in captivity, then you may be sure, providing your treatment of them has been right, that all your brood will arrive at the perfect state.

The next stage we have to consider we will pass over briefly. The change from the larva to the chrysalis is always a very fascinating performance to watch, not that one could sit and see the whole performance right through from start to finish, the time occupied is too long for that. Generally the process lasts a day or two, but by watching at frequent intervals, where several individuals are engaged at the same operation and each at its own stage of the work, it is not difficult to follow the whole process of the transformation. Try it with the larva of the Large Garden White butterfly, perhaps the commonest, and therefore the easiest to procure; you will gather plenty of "stung" or "ichneumoned" examples, but still a sufficient number should be clean to serve your purpose.

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