As with other "wainscots", this species has buffish yellow forewings with prominent venation. The Smoky Wainscot has a dark basal streak with another shorter streak nearer to the costa and tornus. This species has grey hindwings with white margins. The wingspan is 31–38 mm. One or two broods are produced each year and adults can be seen at any time between June and October. It flies at night and is attracted to light, sugar and various flowers.
The larva is brown with dark and white lines and feeds on various grasses including Alopecurus, Dactylis, Deschampsia, Leymus and Phragmites and has also been recorded on the sedge, Carex and the rush, Luzula. This species overwinters as a small larva.
- 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
|Wikimedia Commons has media related to Mythimna impura.|