The female of this species is wingless and rather spider-like and can be found on the trunks and stems of its larval food plants. She is white or yellow and black-patched. The male is fully winged (wingspan 40–45 mm) and very variable. The ground colour of the forewing is pale yellow or light yellow ochre and suffused dark grey.The basal and distal fasciae are dark brown.The basal fascia is bordered on the inner side by a brown cloud; the distal fascia has a brown cloud on the outer edge.There is also a brown cloud along the costa.There are two dark brown oblong spots in the upper half of the terminal area. The hindwing is grey-white with grey suffusion.There is a grey-black discal spot on both wings.There are numerous and significant deviations from this colour pattern and some specimens are very dark. Truly melanic forms are also frequent. As with the peppered moth, the darker forms tend to be prevalent in industrial areas.
The adults have been recorded from September to December in the British Isles. Males are attracted to light.