In H. sylvinus, H. velleda and H. pyrenaicus less abnormal modes of attracting the males occur, the individuals of this latter sex assembling in great numbers at a spot where there is a female. In the first of the three species mentioned the female sits in the twilight on the stem of some plant and vibrates the wings with rapidity; she does not fly; indeed, according to Mr. Robson, she does not till after fertilisation move from the spot where she emerged. In H. pyrenaicus the female is quite apterous, but is very attractive to the males, which as we have said, assemble in large numbers near her. Thus within the limits of these few allied forms we find radically different relations of the sexes.
1. The male attracts the female—(A) by sight (H. humuli); (B) by odour (H. hectus).
2. The female attracts the male—(A) by vibration of wings (H. lupulinus and H. sylvinus); (B) without vibration, but by some means acting at a distance (H. velleda, H. pyrenaicus).
Little or nothing is known as to the habits of the great majority of the more remarkable forms of the family. The gigantic Australian forms are believed to be scarcely ever seen on the wing.
The Hepialidae differ from other Lepidoptera by very important anatomical characters. The absence of most of the mouth-parts is a character common to them and several other divisions of Lepidoptera; but the labial palpi are peculiarly formed in this family, being short and the greater portion of their length consisting of an undivided base, which probably represents some part of the labium that is membranous in normal Lepidoptera. The thoracic segments are remarkably simple, the three differing less from one another than usual, and both meso- and meta-notum being much less infolded and co-ordinated. The wings are remarkable for the similarity of the nervuration of the front and hind wings, and by the cell being divided by longitudinal nervules so as to form three or four cells. On the inner margin of the front wing there is near the base an incision marking off a small prominent lobe, the jugum of Prof. Comstock. Brandt mentions the following anatomical peculiarities,[[288]] viz. the anterior part of the alimentary canal is comparatively simple; the respiratory system is in some points like that of the larva; the heart is composed of eight chambers; the appendicular glands of the female genitalia are wanting. The testes remain separate organs throughout life. The chain of nerve ganglia consists of the supra- and infra-oesophageal, three thoracic, and five abdominal, ganglia, while other Lepidoptera have four abdominal.
Fam. 24. Callidulidae.—A small family of light-bodied diurnal moths having a great resemblance to butterflies. In some the frenulum is present in a very rudimentary condition, and in others it is apparently absent. Cleosiris and Pterodecta are very like butterflies of the Lycaenid genus Thecla. Although fifty species and seven or eight genera are known, we are quite ignorant of the metamorphoses. Most of the species are found in the islands of the Malay Archipelago, but there are a few in East India.
Fam. 25. Drepanidae (or Drepanulidae). (Hook-tips).—The larger moths of this family are of moderate size; many of the species have the apex of the front wing pointed or even hooked; some have very much the appearance of Geometrid moths; they resemble very different members of that family. Oreta hyalodisca is remarkable on account of the very large, transparent patch on each front wing, though the other species of the genus have nothing of the sort. In the genus Deroca we find Insects with the scales imperfect, they being few and small and approximating in form to hairs; in D. hyalina scales are nearly entirely absent. In other genera, e.g. Peridrepana, Streptoperas, there is only a very inferior state of scale-formation. The few larvae that are known are peculiar; they are nearly bare of hair, without the pair of terminal claspers, while the body is terminated by a long tubular process. They form a slight cocoon among leaves.
The members of the family were formerly much misunderstood, and were assigned to various positions in the Order. There are now about 30 genera, and 150 species known, the geographical distribution of the family being very wide. In Britain we have half a dozen species. Cilix glaucata (better known as C. spinula) is said "to undoubtedly imitate" the excrement of birds. No doubt the Insect resembles that substance so as to be readily mistaken for it. This Insect has a very wide distribution in North America, Europe and East India, and is said to vary so much in the structure of its organs as to justify us in saying that the one species belongs to two or three genera.
Fig. 199—Mature larva of Apoda testudo, on beech-leaf. Britain.