_Transformation._--The larval or caterpillar stage having been completed, and full development having been attained, the caterpillar is transformed into a pupa, or chrysalis. Of this, the third stage in the life of the insect, we now shall speak at length.
The caterpillars of many butterflies attach themselves by a button of silk to the under surface of a branch or stone, or other projecting surface, and are transformed into chrysalids, which are naked, and which hang perpendicularly from the surface to which they are attached. Other caterpillars attach themselves to surfaces by means of a button of silk which holds the anal extremity of the chrysalis, and have, in addition, a girdle of silk which passes around the middle of the chrysalis, holding it in place very much as a papoose is held on the back of an Indian squaw by a strap passed over her shoulders.
[Illustration FIG. 23.--Caterpillar of _Anosia plexippus_, undergoing change into chrysalis: _a_, caterpillar just before rending of the skin; _b_, chrysalis just before the cremaster, or hook, at its end is withdrawn; _c_, chrysalis holding itself in place by the folds of the shed skin caught between the edges of the abdominal segments, while with the cremaster, armed with microscopic hooks, it searches for the button of silk from which it is to hang (Riley). (Compare Fig. 24, showing final form of the chrysalis.)]
_The Form of Chrysalids._--The forms assumed by the insect in this stage of its being vary very greatly, though there is a general resemblance among the different families and subfamilies, so that it is easy for one who has studied the matter to tell approximately to what family the form belongs, even when it is not specifically known. Chrysalids are in most cases obscure in coloring, though a few are quite brilliant, and, as in the case of the common milkweed butterfly (_Anosia plexippus_), ornamented with golden-hued spots. The chrysalids of the _Nymphalidæ_, one of the largest groups of butterflies, are all suspended. The chrysalids of the _Papilionidæ_, or swallowtail butterflies, are held in place by girdles, and generally are bifurcate or cleft at the upper end (Fig. 25), and are greenish or wood-brown in color.