It has a wingspan of 27–31 mm (1.1–1.2 in). The wings are greyish white with three irregular black blotches along the costa of the forewing, the largest in the middle. Occasionally, much darker (melanic) forms occur. "Easy to recognize, in spite of its variability. In the typical form the ground colour is dirty whitish and the median band is almost or altogether obsolete in its posterior half.
The species has an exceptionally long flying season spanning two or three broods, and the adults can be seen any time from April to October in the British Isles. This may vary in other parts of its range. It flies throughout the night and is attracted to light – it is one of the species most likely to be seen at lighted windows.
