In this family Staudinger includes 161 species known to occur in the Palæarctic Region. About forty of these are found in Europe, and thirty-one of the latter rank as British species.
The family is usually divided into two sub-families—Arctiinæ and Lithosiinæ, fifteen of our species being referred to the former and sixteen to the latter. In both groups the caterpillars are hairy, but the hairs are usually longer in those of the "Tigers" than in those of the "Footmen"; the latter, too, are lichen feeders, whilst the others prefer the foliage of plants.
The moths in this sub-family have short, or, rather, stout bodies, and ample wings; and as the tongue is imperfectly developed in most of the species, flowers have not the same attraction for them as for the long-winged and slender-bodied Lithosiinæ, most members of which have this organ well developed.
Older English names for this generally distributed and often common species are The Great Ermine Moth of Wilkes (1773), Harris (1778), and The Large Ermine of Haworth.
On Plate 75 will be found three colour-forms of the moth. Fig. 1 has the typical whitish colour, Fig. 2 is creamy on the fore wings, and Fig. 3 has the fore wings buff. The last represents a specimen from Scotland, where, especially in the western parts of the country, and also in the north of Ireland, and the north-west of England, buff forms, both paler and much darker than the one figured, are not uncommon. Sometimes the Scottish specimens have smoky hind wings. As regards the black spots on the wings, the species is subject to considerable variation. In some examples almost all the markings are entirely absent; in others they are very small and numerous, or large in size and number; the central spots on the fore wings are often united, forming irregular designs. Again, there may be an unusual amount of black spotting on the outer margins, and all other parts of the wings free of spots. All these aberrations in marking, except, perhaps, the central cluster, seem to occur in the various colour forms. An uncommon form, known as var. walkeri, Curtis (Plate 78, Fig. 5), has the black scales gathered together into streaks along the nervures of the fore wings; modifications of this variety have also been found, or reared. Possibly by the careful selection of parent moths showing tendency to the streaked aberration it might happen in a generation or two that var. walkeri would turn up in the breeding cage to reward the rearer for trouble taken in the experiment.
The caterpillar, which is often not uncommon in gardens in August and September, or even later, is brown, with long hairs, and a reddish stripe along the middle of the back. It feeds on the foliage of low-growing plants, and does not appear to be specially attached to any particular kind. The chrysalis is dark brown, in a close-fitting cocoon of silk and hair from the caterpillar, spun up in odd corners on the ground or at the base of a wall or fence, sometimes between the pales (Plate 74).
The moth emerges in June, and may be seen sitting on walls, fences, trees, or on the herbage growing on hedge banks; or even on the bare ground. It often flies into houses when lighted up, and is a frequent attendant at the public gas lamps and electric lights. The geographical range of this species extends through Northern and Central Europe southward to North-West Africa, and eastward to Amurland.
The specimens of this white moth, depicted on Plate 75, are of the form usually met with in Britain. To Haworth, Stephens, and other early entomologists this was known by the English name of the "Water Ermine" (S. papyrata, Marsham), whilst a rarer form—with a minute dot on the disc of the fore wings, and three dusky spots on the hind wings, as in the White Ermine—was the "Dingy White" of Haworth. Occasionally specimens are obtained with extra black spots on the basal and front areas of the fore wings.
Caterpillar, dark brown with a purplish tinge, the hairs, arising in spreading tufts from black warts, are dark brownish; spiracles white; head black and glossy. Feeds in July and August on a variety of marsh plants, among which are yellow loosestrife (Lysimachia vulgaris), mint (Mentha aquatica), lousewort (Pedicularis), water dock (Rumex hydrolapathum), and iris. It seems to affect plants growing under bushes, rather than those more exposed. It is, presumably, not difficult to rear in confinement, as there is a record of eight broods belonging to three generations, and all descendants of a captured female, having been reared by Mr. Bacot. Chrysalis dark reddish brown, in a cocoon similar to that of the last species.