Wingspan 42 to 50 mm. One of several similar 'Thorns', the adults of this species can be distinguished by the shape of the cross-lines on the forewing. The inner line is distinctly curved, and the outer line has a 'kink' where it meets the leading edge.

It is very similar to the September Thorn. Perhaps the easiest way to distinguish them is that the September Thorn has all-yellow legs whilst the August Thorn has 'knee socks' where the lower part of the legs is whitish.

The August Thorn also has the line nearest the base of the wing acutely angled at the costa whilst this is almost straight in the September Thorn.

It inhabits woodland and suburban habitats.

Flying in August and September, the species is often attracted to light.

The foodplants are trees such as Oak (Quercus) and Beech (Fagus).

It can be found locally throughout most of Britain. In a recent survey to determine the status of all macro moths in Britain this species was classified as local.

Fairly frequent but not common in Leicestershire and Rutland. L&R Moth Group status = B (scarce resident or restricted distribution or regular migrant).