The Purple Emperor begins his royal career in the curious form shown at fig. 5—a shape unique among British butterflies, as beseems that of their sovereign; and he carries a coronet on his brow already.
All those beautiful little butterflies called the Hair-streaks (fig. 9), the Blues (fig. 10), and the Coppers, have very short and fat caterpillars, that remind one forcibly of wood-lice—a shape shared also by that small butterfly with a big name, the Duke of Burgundy Fritillary (fig. 8), an insect very distinct from the Fritillaries above mentioned with thorny caterpillars.
The legs of a caterpillar are usually sixteen in number, and composed of two distinct kinds, viz. of six true legs, answering to those of the perfect insect, and placed on the foremost segments of the body; and of ten others, called "prolegs;" temporary legs, used principally for strengthening the creature's hold upon leaf or branch.
Like the rest of its body, the caterpillar's head widely
differs in structure from that of the perfect insect, being furnished with a pair of jaws, horny and strong, befitting the heavy work they have to get through, and shaped like pincers, opening and shutting from side to side, instead of working up and down after the manner of the jaws in vertebrate animals. This arrangement offers great convenience to the creature, feeding, as it is wont to do, on the thin edge of a leaf. It is a curious sight to watch a caterpillar thus engaged. Adhering by his close-clinging prolegs, and guiding the edge of the leaf between his forelegs, he stretches out his head as far as he can reach, and commences a series of rapid bites, at each nibble bringing the head nearer the legs, till they almost meet; then stretching out again the same regular set of mouthfuls is abstracted, and so on, repeating the process till a large semi-circular indentation is formed, reaching perhaps to the midrib of the leaf; then shifting his position to a new vantage ground, the marauder recommences operations, another sweep is taken out, then another, and soon the leaf is left a mere skeleton.
But a change, far more important than mere skin-shifting, follows close upon the animal's caterpillar-maturity, complete as soon as it ceases to grow.
The form and habits of a worm are to be exchanged for the glories and pleasures of winged life; but this can only be done at the price of passing through an intermediate state; one neither of eating, nor of flying, but motionless, helpless and death-like.
This is called the Chrysalis or Pupa state.
Pupa is a Latin word, signifying a creature swathed, or tied up; and is applied to this stage of all insects, because all, or some, of their parts are then bound up, as if swathed.