Sexes are sexually dimorphic. Males have a slender body and wingspan of 30-40 mm. Forewings brownish to grey-brown with wavy dark bands across the forewing. Females of the European subspecies are flightless. Females have a wingspan of ca. 40-70 mm. Forewings are white with wavy black bands across the wing. The abdomen is distended with eggs and white with yellowish hairs.
First instar larvae are ca. 3 mm in length and greyish black with a dark head. Final instars reach 40-70 mm in length (females being larger than males). The body is colourful with black, yellow, blue and red patterns. Head is yellow. Two rows of blue tubercules are present dorsally on the first 5 segments and 2 rows of red tubercules on the following segments.
Pellet shaped, ca. 1 mm in diameter and grey in colour. Laid in small clusters or larger masses, covered in a yellowish coating of hair sloughed off abdomen of female. Typically laid on trunks and lower branches but also rocks, walls and fences.
Two strains (European and Asian) present in Europe, the Middle East, North America, Algeria and Asia
A wide range of deciduous and coniferous tree species, with a preference for oak and aspen.
Larvae initially feed on developing buds before feeding on new leaves. Large populations can entirely defoliate trees. Bristles from the larvae cause skin rashes and asthma issues.