Illustration from John Curtis's British Entomology Volume 6
The wingspan is 27–35 mm. The ground colour is light brown or white brown to reddish brown.The forewings, which exhibit a fine regular pattern of dark, finely serrated lines have a dark eye patch in the middle. Under the sickle, or on the outer part of the outer edge of the wing, there is a purple stain. From the wing tip, a clearly curved, dark brown band runs under the stain up to the edge of the wing. The hindwings are also light brown in colour, but brighter than the forewings. Their pattern is similar to but not so strong as that of the forewings. In the females the hindwings are white with the same dark patterning. The egg is yellow marked with orange at one end. The last instar caterpillar is green, the dorsum reddish-brown, except towards the black-marked yellowish head. There are two conspicuous warts on rings two to five, and less obvious raised spots on the other rings, all bearing hairs. In the younger stages it is blackish, with white marks on the fourth and seventh rings; later it becomes greenish below, and the markings on the back of rings four, seven, eight, and ten are whitish or creamy.
The moth flies from April to August depending on the location.