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The moth emerges in May, sometimes at the end of April, generally in the afternoon; it sits on the tree trunk to expand and dry its wings, and then ascends higher up the tree. It is found in Berkshire, Buckinghamshire, and in most of the southern counties of England, and in the west, but it seems to be rarer eastward and northward, and also in Scotland. In Ireland it has been found, very sparingly, in Wicklow and Kerry, and "numbers were taken in a moth trap at Clonbrook."
The range abroad is very similar to that of the next species.
The Swallow Prominent (Pheosia tremula).
Normally whitish, with a brown shaded black stripe along the inner margin of the fore wings, and a brownish cloud, with black streaks in it, towards the tips of these wings; the outer extremities of the veins are white, there is a white wedge-shaped streak between veins 1 and 2, and from the apex of this an indented white line runs to the base of the wing. Sometimes the whole discal area is suffused with brownish. The moth is shown on Plate [28], Figs. 4, 5, and the early stages on Plate [29], Figs. 2, 2a, and 2b. The egg when laid is creamy white, and the newly hatched caterpillar is pale green. When full grown the caterpillar is green with rather darker, but not always clearly defined, lines along the back, and a yellow line along the region of the black spiracles; the underside is sometimes reddish. Another form is brownish in colour and the yellow line is then generally obscure. The green form is figured on Plate [29]. The usual food is poplar, but sallow is also eaten. It may be found in late June and early July and again in September and October. The chrysalis is reddish brown and glossy except on the wing covers, which are granulated and appear darker. The cocoon is roughly constructed of silk and earth, and before spinning it the autumnal caterpillar sometimes burrows a good depth under the surface of the soil; the summer cocoons are said to be made up among leaves. The moth is on the wing in May and August.
The species is perhaps most common in the southern and eastern counties of England, but seems to be pretty generally distributed throughout the country, and extends into Scotland as far as Moray. In Ireland it has a wide range but is only common near Londonderry. Abroad it is found in Central and Northern Europe, and as far east as Amurland and Ussuri. In America it is represented by P. dimidiata, H.-S., which does not seem to be really specifically distinct.
The Lesser Swallow Prominent (Pheosia dictæoides).
Very similar to the last species, but generally smaller, and the ground colour has usually less brown in it; the chief character, however, by which it may be distinguished, is the broader and clearer white wedge-shaped mark between veins one and two on the fore wings. Reference to the figures of each species on Plate [28] will show this at once.