The wingspan is 21-23 mm and the forewings are warm brown with two black spots along the costa with a black discal spot completing a distinctive triangle. There is a narrow pale line near the fringe with a distinct whitish spot near the tornus, although this is not as prominent as in the rather similar Currant Pug. The hindwings are greyish brown. The species flies at night in June and July  and is attracted to light.
As the name suggests, the larva feeds on the flowers of mugwort (which is sometimes called "Common Wormwood") but will also feed on the flowers of a range of other plants (see list below). The species overwinters as a pupa.
Recorded food plants
- Calluna - Heather
- Cirsium - Creeping Thistle
- Pimpinella - Burnet-saxifrage
- Solidago - Goldenrod
- Tripleurospermum - Mayweed
- Chinery, Michael. Collins Guide to the Insects of Britain and Western Europe (1986, reprinted 1991)
- Skinner, Bernard. Colour Identification Guide to Moths of the British Isles (1984)