The New International Encyclopædia/Swallowtail

SWALLOWTAIL. Any member of a family of large butterflies, Papilionidæ, with tail-like prolongations of the hind wings. Black, yellow, blue, and green are the prevailing colors. About 25 species occur in the United States. South America is most rich in these butterflies. About 700 species have been described in all. The larvæ of the swallowtails possess a curious process on the thorax called an ‘osmaterium,’ which is usually retracted, but may be thrust forth at will. It is a Y-shaped process and contains a scent-gland which emits a strong odor when the organ is thrust out. The pupa is placed with the head upward, fastened by the tail to the supporting object, and is kept in place by a silk band around the middle of the body. (See Butterflies; also Plate under Butterflies, Fig. 5.) In certain species the males and females differ so much both in form and coloration that they might easily be mistaken for distinct species. In New Guinea there occurs a swallow-tail butterfly (Ornithoptera paradisea) the female of which is black, white, and gray, and the male is gold and green, with very long tails on the hind wings. The males of another species of the same genus are numerous and the female is rare; the proportion is said to be about 1000 to 15. Not only does the female show sexual dimorphism, but even considerable seasonal dimorphism. The tiger swallowtail (Jasoniades glaucus) is a North American species which shows a striking sexual dimorphism in a portion of its range. The form now known as Turnus is straw-colored above, banded and marked with black. In the South and West black forms of the female sex occur, and belong to the so-called ‘glaucus’ form. The caterpillar of these two forms is dark green with two purple eye-spots, one on each side of the third thoracic segment, which are bordered with black, yellow, and black again in turn. When not feeding, this caterpillar rests on a bed of silk spun on a leaf. The zebra swallowtail (Iphiclides Ajax) presents one of the most striking cases of seasonal dimorphism known among butterflies, so that until the life-history of this form was known three different species had been described from it. There are several broods a season and the last brood winters in the chrysalis stage. The butterflies that appear in the early spring are known as the Marcellus form and those that appear later in the spring as the Telamonides form. The latter are larger butterflies with longer tails and more white than the Marcellus form. (See Colored Plate of American Butterflies.) All the late spring broods produce a third form which is still larger and with longer tails. This summer brood is known as the Ajax form. See illustration at Skipper.