The moths emerge in June, and from their eggs caterpillars result in July. These, feeding up quickly, attain the perfect state in late July or early August. Caterpillars from this second generation usually go into hibernation when quite small, and feed up in the following April and May; in confinement they may, however, get through their metamorphosis and reach the moth state in September or October. Sometimes it happens that a part of the summer brood of caterpillars will feed up straight away and produce moths in August; others, feeding and growing more slowly, assume the winged state in November; whilst a third portion will remain small and go into hibernation.
This very local species used to be obtained in the Wimbledon district, but it has not been seen there for some years past. { 96} Other localities for it are the Norfolk and Cambridge fens, Bewdley Forest in Shropshire, and Wyre Forest, Worcestershire; it is also found in some parts of Devonshire, Suffolk, Essex, and Yorks. Its range abroad extends through Northern and Central Europe, southward to North Spain, Piedmont, and Corsica, and eastward to Amurland, Corea, and Japan.
The male has the wings rather more ample than the same sex of the last species, the colour is a more ochreous red and there is a large white spot at the lower angle of the fore wings, but no white mark at the tips of these wings. Specimens from the north of England are rather darker than southern examples. In the course of temperature experiments it has been noted that the colour of the moth is darkened if the chrysalids are put in a refrigerator for a few weeks, and then brought into a mean temperature of 40° Fahr. In the female the appendages representing wings are somewhat larger than those of the female of the Scarce Vapourer, but are quite useless as organs of flight (Plate 40, Figs. 4, 6).
In general colour the caterpillar is violet or smoky grey; the markings on the back comprise a creamy, red-dotted line along the middle area, this is edged with black, and on each side of it is a series of raised red spots; the broken line along the sides is yellowish, and the four brushes of hair on the back are yellow, sometimes merging into brown above; the pencils of longer hairs are blackish on the ring nearest the head, and dark grey or brownish on the last ring. It may be found through the summer on the leaves of most trees and bushes. Chrysalis blackish, glossy, and rather hairy. The cocoons are spun up in the crevices of bark on tree trunks, or in the fork of a twig, under the eaves of an out-house or shed, on palings and fences, etc. The hairs of the caterpillar are mixed with the silk of the cocoon; the female lays her pale brownish eggs, which are minutely pitted and have a darker ring below the sunken top, on the outside of the cocoon, and there they remain through the winter.