Having attained its full growth the instincts of the caterpillar undergo a change. It ceases to eat and begins to weave a couch or cocoon round about itself by which it is finally more or less enclosed. It then throws off the caterpillar or larval skin and appears in the third stage.
This state of its existence seems to me the most mysterious and therefore the most interesting. More than one of these cocoons have I found attached to walls, fences, limbs and in similar places, looking as though they were but the dried-up remains of some species of insect life. But there was life within them, a germ which sooner or later would spring forth in all the wonderful beauty of the moth or the butterfly.
This third period is termed the pupa, nymph or chrysalis state. Its duration varies from a few weeks to several months, according to the time of year at which it enters this stage. The common Cabbage Butterfly, which rears two broods during the season, is quickest to make the change, only a few weeks of the pupa form being necessary. Some remain in the chrysalis a month or more, appearing in the butterfly form at the close of the summer. Those becoming encased in autumn are like the hibernating animals in many respects, lying dormant the winter through. The only sign of life ever discovered in the pupa is a convulsive twitching when irritated, and for this reason those who know nothing of the hidden beauties of butterfly life miss a great deal of pleasure in not being able to study the seemingly lifeless chrysalis.
When mature the pupa case cracks toward the anterior end, and the butterfly or moth crawls forth with wings which, though at first small and crumpled up, in a few hours attain their full size. As soon as they are strong enough the new creature mounts upon them and, if it be a butterfly, flies out into the sunlight; while the moth hies away to some dark corner until nightfall, then for the first time in its existence it rises upon wings to enjoy the summer zephyrs.
I remember having watched one butterfly leave the chrysalis and, though but a child at the time, I shall never outlive the impressions which that rare pleasure left with me. It was one of the large-winged, black-white-and-yellow fellows which every one admires so much, and which species is regarded as a treasure here in these Central States. Little by little the ugly casing opened, and when I first saw the baby butterfly he was like a tiny mass of mingled colors, with neither life nor shape to give me an idea of the sort of creature into which he would develop. Soon he began to move uneasily, like a child awaking out of a long sleep; then he stretched his wings leisurely as though proud to have found them at last. Next he drew himself up and finished bursting his paper-like shell, gained a foothold on the plank on which we had placed him and looked about with a, seemingly, very much surprised though gratified air. Meanwhile he kept working his wings and stretching them anon, very impatient because of their, to him, slow growth. At last he gained the confidence to try them, and within an hour from the time we first saw him he had arisen and flown away into the sunshine to seek his place in the world.