Wingspan 11-20 mm.
Quite a variable species, with some individuals being almost unicolorous, others with a pale streak along the fore edge of the darker brown wing, and some with obvious darker patches on a mottled forewing.
It is also very variable in size and easily confused with other Bactra species.
Rather common throughout Britain, it occupies marshes and heaths, and the larvae feed on various rushes including Juncus and Scirpus.
The adults are readily attracted to light and are on the wing in two generations between July and October.