THE THIRD OR PUPAL STAGE
When the caterpillar is fully grown it spins a little silken button on some solid object, hangs itself up by the tail, and undergoes a final moult. When the old skin peels off this time it reveals, not a caterpillar with a bright new skin, but a different sort of creature altogether. The apparently lifeless pupa or chrysalis shows some of the characteristics of a butterfly, but the wings and legs are folded up, the antennae are cemented fast against the body, and the whole structure covered by a horny, tight-fitting sheath. This state of affairs usually lasts only three or four weeks, but some butterflies, particularly in temperate climates, pass the winter in the pupal state.
THE FOURTH STAGE OR IMAGO
When the chrysalis stage is over the outer skin bursts open about the head, and the imago—the butterfly proper—crawls out. The newly emerged butterfly is a sorry-looking specimen; the wings are very small and flaccid, and it can do no more than cling to some convenient support, usually the empty skin of the chrysalis. After a while, however, the body juices flow out into the wings, which expand and harden, and in a few hours the young butterfly is flitting from flower to flower with its fellows.
Ordinarily the imago does not live long—often only a few days. Just as the caterpillar’s sole business is to eat, the mature butterfly has only one important function, and that is reproduction. It speedily finds a mate (that’s what its wings are for), contributes its quota of ova or sperm to produce another generation of caterpillars, and its ephemeral existence as a butterfly is over.
CHAPTER IV
THE CASE OF THE RED SILVERWING
Having dealt briefly with the transformations of butterflies in general, it may be well to examine more closely into those of a single representative species. For this purpose I have chosen Dione vanillae, known as the Red Silverwing, and have described each stage and transition in considerable detail. The following paragraphs are extracts from the daily records of a study I made in southern Kansas, the northern limit of vanillae’s usual range.
OVIPOSITION
“One of the females, alighting upon the upper side of a leaf within ten inches of my face, suddenly elevated the forward part of the body, brought the wings together vertically, curved the abdomen slightly forward, and drew its tip slowly across the surface of the leaf for a distance of approximately 12 mm. Remaining quiet for an instant, it lifted the abdomen, showing an egg firmly attached to the leaf. The eggs are laid singly, usually in the upper middle of the leaf. I have never seen more than one upon the same leaf.”