Fig. 226.—A, Head of a Lepidopterous insect; B, the labium; Ant., feeler; E, eye; Lab. Pa., labial palp; Mx. 1, proboscis; Mx. Pa., maxillary palp (magnified).
In short, the whole organisation of a butterfly is definitely adapted to the special duties which belong to this period of its life. The growing stage is over; the sole object of life is now to seek a mate and—in the case of the female—to lay the eggs in a place where the future larvae may find plenty of food. Ease of locomotion and conspicuousness are secured by the broad and brilliantly-coloured wings; the peculiar manner of flight is considerable protection against the attacks of birds; large eyes aid in the recognition of the mate; and a concentrated and easily-digested food is supplied by the nectar of flowers, and made accessible by the long, sucking proboscis—the service of cross-pollination ([p. 92]) often being unconsciously rendered in return for the sweet draught.
The common species of cabbage-white butterflies spend the winter as pupae; the perfect insects emerge in April, lay their eggs, and then die. The caterpillars pupate and a second generation of butterflies appears, their offspring reaching the pupa stage about the end of autumn.
Moths.—Moths pass through a life-history which is identical, in its broad features, with that of butterflies. The larva which hatches from the egg is a caterpillar, whose life is spent in feeding and growing. At the same time the external features of the adult are gradually taking form under the skin. When at last the full larval size is attained, and a resting stage is necessary for the perfection of the internal organs, the caterpillar’s skin splits, and is shed, and the animal becomes a pupa or chrysalis. A moth-pupa is generally somewhat egg-shaped ([Fig. 227]), whereas the pupa of a butterfly is usually conical, though there are many exceptions.
The winged moth, which at length emerges from the pupal skin, differs from a butterfly in certain obvious respects. Its body is usually broad and thick; its feelers are either comb-like or thread like, not knobbed at the ends; the two wings of one side are in most cases secured together at the base by one or more bristles on the hind-wing hooking over a catch on the fore-wing; in rest, the wings usually slope and are not fully extended. Whereas butterflies usually fly only in the sunshine, moths often fly by night, and the flowers which night-flying moths frequent for nectar are as a rule white and strongly-scented, and close during the day. In finding their mates, moths seem to depend largely upon the sense of smell, which is probably lodged in the feelers.
Fig. 227.—Stages of Tiger Moth. A, Caterpillar, from left side; B, pupa (removed from cocoon), ventral view; C, perfect insect (female). (From a photograph by Mr. A. Flatters.) (× ⁵/₇.)
The life-history of a typical moth is well exemplified by the Tiger Moth ([Fig. 227]), which is easily reared in captivity. The larva—often called the “woolly bear,” from its thick covering of hair—may be found in early summer on the leaves of lettuce, strawberry, nettle, and other plants. It pupates about the end of June, working its hair, together with silk spun by the spinneret, into a cocoon, in which the resting stage is passed. About a month later the perfect moth emerges; its fore-wings are beautifully mottled with cream colour and chocolate brown; the hind-wings are red, with metallic violet spots. The feelers of the male are comb-like, and are probably very sensitive organs of smell, by means of which he seeks out his mate. The female’s feelers are thread-like.