63 - 70mm
The upper wings are white with a large dark patch on the tip of the fore-wing, (grey in the spring brood, black in the summer brood), and there are also two black spots across the forewings. The under forewings display two black spots on both sexes, and the under hindwings are tinged yellow. The summer (second) brood is deeper coloured.
The first generation is on the wing from April to June and the second generation from July until September.
The species first appeared in written records of this country in 1666.