Page:EB1911 - Volume 16.djvu/495

Rh is tropical in its distribution, but the common silkworm (Bombyx mori, fig. 48) has become acclimatized in southern Europe and is the source of most of the silk used in manufacture and art. Of commercial value also is the silk spun by the great moths of the family Saturniidae, well represented in warm countries and contributing a single species (Saturnia pavonia-minor) to the British fauna. These moths (fig. 49) have but a single anal nervure in the hindwing and only three radial nervures in the forewing. The wing-patterns are handsome and striking; usually an unsealed “eyespot” is conspicuous at the end of each discoidal areolet. The caterpillars are protected by remarkable spine-bearing tubercles (fig. 10, B).

This group stands at the base of the series of families that are usually distinguished as “butterflies.” The feelers are recurved at the tip, and thickened just before the extremity. The forewing has the full number of radial nervures, distinct and evenly spaced, and two anal nervures; the frenulum is usually absent. The larvae (fig. 51) have prolegs with complete circles of hooklets, and often feed in concealed situations, while the pupa is protected by a light cocoon. The affinities of this group are clearly not with the higher groups of moths just described, but with some of the lower families. According to Meyrick they are most closely related to the Pyralidae, but Hampson and most other students would derive them (through the Castniidae) from a primitive Tineoid stock allied to the Cossidae and Zygaenidae.

Three families are included in the section. The North American Megathymidae and the Australian Euschemonidae have a frenulum and are usually reckoned among the “moths.” The Hesperiidae in which the frenulum is wanting form the large family of the skipper butterflies, represented in our own fauna by several species. They are insects with broad head—the feelers being widely separated—usually

brown or grey wings (fig. 50) and a peculiar jerky flight. The family has an extensive range but is unknown in Greenland, New Zealand, and in many oceanic islands.

This group comprises the typical butterflies which are much more highly specialized than the Grypocera, and may be readily distinguished by the knobbed or clubbed feelers and by the absence of a frenulum. Two or more of the radial nervures in the forewing arise from a common stalk or are suppressed. The egg is “upright.” The larvae have hooklets only on the inner edges of the prolegs. The pupa is very highly modified, only two free abdominal segments are ever recognizable, and in some genera even these have become consolidated. The cocoon is reduced to a pad of silk, to which the pupa is attached, suspended by the cremastral hooks; in some families there is also a silken girdle around the waist-region. In correlation with the exposed condition of the pupa, we find the presence of a specially developed “head-piece” or “nose-horn” to protect the head-region of the contained imago. Their bright colours and conspicuous flight in the sunshine has made the Rhopalocera the most admired of all insects by the casual observer.

A modification that has taken place in several families of butterflies is the reduction of the first pair of legs. H. W. Bates arranged the families in a series depending on this character, but neurational and pupal features must be taken into account as well, and the sequence followed here is modified from that proposed by A. R. Grote and J. W. Tutt.

The Lycaenidae are a large family including the small butterflies (figs. 52, 53, 54) popularly known as blues, coppers and hairstreaks. The forelegs in the female are normal, but in the male the tarsal segments are shortened and the claws sometimes are absent. The forewing has only three or four radial nervures (fig. 55), the last two of which arise from a common stalk; the feelers are inserted close together on the head. The larva is short and hairy, somewhat like a woodlouse in shape, the broad sides concealing the legs and prolegs, while the pupa, which is also hairy or bristly, is attached by the cremaster to a silken pad and cinctured with a silken thread. The upper surfaces of the wings of these insects are usually of a bright metallic hue—blue or coppery—while beneath there are often numerous dark centred “eye-spots.” The family is widely distributed. Nearly related are the Lemoniidae, a family abundantly represented in the Neotropical Region, but scarce in the Old World and having only a single European species (Nemeobius lucinia) which occurs also in England. In the Lemoniidae (figs. 56, 57) the forelegs of the male are reduced and useless for walking. The Libytheidae may be recognized by the elongate snout-like palps, 