Although some English specimens approach the larger and whiter typical form, the species as it occurs in the British Isles is generally greyer, var. griseata, Staudinger; two examples of this form are shown on Plate [83], Figs. 10 and 11. In the Shetland Isles, the species assumes a darker coloration, and is either well marked on the fore wings, as in Fig. 14, or almost plain, as in Fig. 13 (ab. thules, Weir), which is an extreme aberration of the form subfasciaria, Boheman. In other examples of a deep leaden grey, or brown tint, the central area is no darker than the rest of the wing. In the Isle of Lewis a white form with faint markings is prevalent, and this leads up to a clear white aberration devoid of markings, ab. niveata, Stephens, = hebudium, Weir.
The wrinkled caterpillar, which feeds, in July and August, on the seeds of the yellow rattle (Rhinanthus crista-galli), and lives in the capsule, is whitish, inclining to greenish, dotted with black, and striped with dark green on the back and sides; head, black and glossy; plates and first and last rings of the body dusky. (Plate [84], Fig. 1.)
The moth is out in May and June, sometimes later. It occurs chiefly in dry meadows where the yellow rattle flourishes, and is to be seen on the wing, often in large numbers, in the late afternoon about sundown. Generally abundant in suitable places, throughout the British Isles.
The Barred Rivulet (Perizoma bifasciata).
Haworth described two forms of this species, and a specimen of each is shown on our Plate [83]. Fig. 4 represents bifasciata (bifaciata, the Double-barred Rivulet), and Fig. 5 depicts
unifasciata (the Single-barred Rivulet). The chief difference appears to be that in the type (bifasciata) the "rivulets" are white and distinct, thus bringing out a dark band between the central one and the base of the wing.
The stoutish caterpillar is pale brown, inclining to ochreous on the back, along which are three lines, the central one greyish, and the others whitish shaded with greyish; a whitish stripe low down along the sides; the usual dots are black, and the spiracles are black, margined with ochreous (adapted from Fenn). In September and October it feeds in the seed capsules of Bartsia odontites, and is often plentiful; Mr. G. F. Mathew records obtaining nearly five hundred from three small bundles of the food plant gathered in the Harwich district.
The moth is out in July and August, but is not often seen in the daytime, and is not taken very frequently, even when flying at night, but it comes to light, and visits flowers.
From chrysalids obtained from caterpillars reared in 1900, Mr. Robert Adkin bred ten moths in 1901, eleven in 1902, two in 1903, five in 1904, and two in 1905.
The species is widely distributed over England, Wales, and the south of Scotland, but it is most frequent in the south of England. Not much is known of it in Ireland, but it has been noted from counties Dublin, Louth, and Derry.