July. Alder, sallow, and lime have also been mentioned as food plants.
The rough, blackish, or sooty-brown chrysalis is enclosed in a coarse netted cocoon, dark brown in colour, and more or less covered with moss, leaves, or other material, among which it is spun up, generally on the ground, but sometimes just under the surface. Assisted by the points on the rings of the body, the chrysalis is able to work itself partly out of the cocoon, and this it does some days before the moth emerges.
The moths usually emerge in late March and in April, earlier or later in some seasons. They do not always come up the year after pupation, but often remain two or more winters in the chrysalis.
The males fly in the sunshine, and are very strong on the wing; the females are not active until dark. This sex has been found resting on the twigs of birch, also on heather, and occasionally on a tree trunk. The males "assemble" freely to a freshly emerged female. The species inhabits the more open parts of woods and forests, moors and hillsides where birches flourish. It is probably more plentiful in its Scottish localities, such as Rannoch and Forres, than elsewhere, but it occurs also in Aberdeenshire, Kincardineshire, and Argyllshire. In England it seems to be not uncommon in Wyre Forest, Worcestershire, and the Reading district in Berkshire. It used to be so plentiful in Tilgate Forest, Sussex, that over a hundred males were brought to the net in one day by a bred female put down to allure them. This happened some fifty years ago, and compares curiously with a record of one male attracted by a female in Tilgate Forest, April 13, 1869. Other localities in Sussex that have been mentioned are St. Leonard's Forest and near Petersfield; it has also been found in Herefordshire and in some parts of Suffolk. Distributed over Central and Northern Europe, the range extending to North Italy.
| Pl. 66. |
| 1, 2. Emperor Moth, males; 3 female. |
| Pl. 67. |
| Emperor Moth. |
| Eggs, natural size and enlarged. |
| Caterpillars and cocoon. (Photos. by W. J. Lucas.) |