Fam. 21. Arbelidae.—Closely allied to Cossidae, but without frenulum, and with less complex wing-nervures. A small family believed to be similar to Cossidae in the life-history. The tropical African Arbelidae are considered by Karsch to be a distinct family, Hollandiidae.
Fam. 22. Chrysopolomidae.—This family has been established by Dr. Aurivillius[[282]] for an African genus, allied in wing-nervuration to Cossidae; the Insects are like Lasiocampidae.
Fam. 23. Hepialidae (Ghost- and Swift-Moths).—Moths of very diverse size, some gigantic; wings not fitting together well at the bases; without a frenulum; no proboscis; the scales imperfect; the nervures complex. The Hepialidae are extremely isolated amongst the Lepidoptera; indeed, they have really no allies; the conclusion that they are connected with the Micropterygidae being certainly erroneous. Although but small in numbers—only about 150 species being known—they exhibit a remarkable variety in size and colour. Many are small obscure moths, while others are of gigantic size—six or seven inches across the wings—and are amongst the most remarkably coloured of existing Insects. The great Charagia of Australia, with colours of green and rose, bearing white spots, are remarkable. The South African Leto venus is of large size, and has an astonishing supply of glittering metallic splashes on the wings, making a barbaric but effective display. The South Australian Zelotypia staceyi, of enormous size, is also a handsome moth; but the majority of species of the family are adorned only in the feeblest manner.
Very little is known as to the larvae; they are either subterranean, feeding on roots, or they live in the wood of trees and shrubs. They are nearly bare, and are apparently the lowest type of Bombycid larva. At the same time, it would appear there is considerable variety amongst them. Packard says[[283]] the young larva of Hepialus mustelinus has the arrangement of setae that is normal in Tineidae. The larva of H. humuli seems to be a very simple form, but H. hectus shows a considerable amount of divergence from it. They probably live for several years; the larva of H. argenteo-maculatus in North America lives for three years, at first eating the roots of Alder and then entering the stems. The pupae are also peculiar. They are of unusually elongate, cylindrical form, with comparatively feeble integument, but with a considerable development of chitinous, elevated, toothed ridges, on the dorsal aspect, and a very strong ridge of this kind on the ventral surface of the seventh segment; the wing-sheaths are short; it is very difficult to distinguish the full number of abdominal segments. These pupae are remarkably agile, and by wriggling and kicking are able to move a considerable distance; it is said that they can force themselves to the surface even when the superficial soil is quite hard. We cannot consider this pupa naturally placed amongst either the pupae obtectae or incompletae of Chapman.
Fig. 198—Pupa of Hepialus lupulinus. Britain. A, Ventral; B, dorsal aspect.
We have already remarked that little is known as to the life-histories. The species are probably prolific, a female of H. thule having been known to deposit more than 2000 eggs. Of the Australian forms little more is known[[284]] than that they live in the wood of trees and shrubs, and are rapidly disappearing; we may fear that some are extinct without ever having been discovered, and others, also unknown but still existing, may disappear only too soon; the wasteful destruction of timber in Australia having been deplorable.
The peculiar habits of the Hepialidae are not likely to bring the Insects to the net of the ordinary collector, and we believe they never fly to light, hence it is probable that we are acquainted with only a small portion of the existing species; their distribution is very wide, but Australia seems to be their metropolis, and in New Zealand twelve species are known. The genera as at present accepted are remarkable for their wide distribution. Leto is said to occur in South Africa and in the Fiji Islands; but we must repeat that the study of these interesting Insects is in a very primitive state, and our present knowledge of their distribution may be somewhat misleading.
The habits of the European Hepialus in courtship have been observed to a considerable extent and are of great interest, an astonishing variety and a profound distinction in the methods by which the sexes are brought together having been revealed.
H. humuli, our Ghost-moth, is the most peculiar. Its habits were detected by Dr. Chapman.[[285]] The male is an Insect of exceptional colour, being white above, in consequence of a dense formation of imperfect scales; the female is of the brownish tints usual in Swift-moths. In the month of June the male selects a spot where he is conspicuous, and hovers persistently there for a period of about twenty minutes in the twilight; his colour has a silvery-white, glistening appearance, so that the Insect is really conspicuous notwithstanding the advanced hour. Females may be detected hovering in a somewhat similar manner, but are not conspicuous like the male, their colour being obscure; while so hovering they are ovipositing, dropping the eggs amongst the grass. Females that have not been fertilised move very differently and dash about in an erratic manner till they see a male; they apparently have no better means of informing the hovering male of their presence than by buzzing near, or colliding with him. Immediately this is done, the male abandons his hovering, and coupling occurs. There can be little doubt that the colour of the male attracts the female; but there is a variety, hethlandica, of the former sex coloured much like the female, and in some localities varieties of this sort are very prevalent, though in others the species is quite constant. This variation in the colour of the males is very great in Shetland,[[286]] some being quite like the females. In H. hectus the two sexes are inconspicuously and similarly coloured. The male hovers in the afternoon or evening in a protected spot, and while doing so diffuses an agreeable odour—said by Barrett to be like pine-apple—and this brings the female to him, much in the same manner as the colour of H. humuli brings its female. The hind legs of the male are swollen, being filled with glands for secreting the odorous matter.[[287]] This structure has led to the suggestion of the generic name Phymatopus for the Insect. Turning to other species of the genus, we find that the normal relative rôles of the sexes are exhibited, but with considerable diversity in the species. In H. lupulinus the males fly about with rapidity, while the female sits on a stem and vibrates her wings; she thus attracts the males, but they do not perceive her unless happening to come within three or four feet, when they become aware of her proximity, search for and find her. It is doubtful whether the attraction is in this case the result of an odour; it would appear more probable that it may be sound, or that the vibration of the wings may be felt by the male.