The fore wings are pale yellow inclining to ochreous, and the front edge is more or less tinged with the same colour as that of the oblique stripe from the tips of the wings to the middle of the inner margin. In the type, this stripe is purplish-brown, but in ab. labda, Cramer, it is crimson, and in ab. atrifasciaria, Stefan, it is blackish. In ab. sanguinaria, Esper, the ground colour is pinkish. The hind wings are always white. (Plate 54, Figs. 1 and 2.)
From 1857, in which year the first specimen recorded as British was captured in September at Plymouth, to 1874, one or more examples of this interesting migrant seem to have occurred during the autumns of most years, in some part of the British Isles, but chiefly in the South of England. The years in which it was apparently unrecorded were 1860, 1861, 1870, 1872, and 1873. Since 1874 there have been very few records. In 1879 a male specimen was taken at Chingford, Essex, August 17th, and a female (ova obtained) on September 1st; a specimen occurred at Christchurch, Hants, October, 1893; a male was obtained in the Isle of Purbeck, Dorset, September, 1895, and one was secured at Timoleague, Co. Cork, in August, 1898; one was accounted for at Malvern, Worcestershire, in August, 1901; a female in fine condition was captured, as it flew in the sunshine over a Cambridgeshire meadow, in the autumn of 1906. Mr. H. M. Edelsten obtained a male specimen in South Devon, on September 12, 1908. The largest number of specimens appears to have been recorded in 1867, when nearly thirty were secured, and of these four were taken in May in the Isle of Wight, where also two females were captured on August 14th and 16th, and one specimen on September 3rd. Six or seven occurred during August in Lancashire, and three in Perthshire, also in August.
The long caterpillar is variable, but is usually some shade of green above, inclining to whitish beneath, and yellowish between the rings; the lines along the back are paler green, reddish, and olive green. It feeds on low-growing plants, such as knotgrass and dock, and has been reared from the egg in August and September. If eggs were obtained in May it would be possible to raise two generations of moths, or, perhaps, even three, during the year.
The species is an inhabitant of Southern Europe and North Africa, and its range extends to India, Madeira, and the Canaries. In Central Europe, including the British Isles, its occurrence is always a more or less casual event.
—It is possibly incorrect to assign this species to Sterrha, Hübner, which is adopted by some authors for the Acidaliid ochraria. There is, however, considerable doubt among authorities about accepting the Hübnerian genus, but Herrich-Schäffer's genus Sterrha appears to be valid and is here employed. If it has to give way, Pseudosterrha, Warren, or Rhodometra, Meyrick, may have to be used.
Lythria purpuraria has long been reported as a British species, but there does not appear to be any very convincing record of its capture in the British Isles. It is widely distributed in Europe, and generally common. As it is a sun-loving insect, it could hardly escape detection if it occurred in any part of our isles. A note by Mr. V. R. Perkins, in The Zoologist for 1861, p. 7449, should, however, not be overlooked. This refers to the capture, on June 18th, of two male specimens that were disturbed from broom, "not far from the city of Perth, by Mr. D. P. Morrison."
Two ordinary examples of this species are shown on Plate 54, Figs. 4, 5. The ground colour is greyish, ranging in one direction to whitish, and in the other to brownish; on the fore wings there are three cross lines, usually reddish-brown in colour, but sometimes dark brown inclining to blackish; the first of these lines is always slender and sometimes very indistinct; the second is often shaded on its outer edge, and the third on its inner edge, with brownish; occasionally the space between the second and third is more or less dusky, especially on the lower half; sometimes these two lines approach each other very closely on the inner margin; the short oblique streak from the tip of the wing to the wavy submarginal line, and also the blackish central dot, are far more distinct in some specimens than in others.
The long stick-like caterpillar is pale ochreous brown, often striped with darker brown or blackish. It feeds on furze (Ulex) and broom (Cytisus), from August to April. The moth is out in May and June, earlier or later according to the season, and is to be found almost everywhere that its food plants flourish.