The forewings of this species share the pale buffish ground colour and prominent venation of other "wainscots" but has much stronger dark markings than most of its relatives, including a thick black basal streak which gives it its common name. The hindwings are dingy grey or brown with lighter fringes. The wingspan is 35-42 mm. This species flies at night in June and July and is attracted to light and sugar.
The larva feeds on various grasses including Deschampsia and Festuca. The species overwinters as a full-grown larva in a cell beneath the surface of the soil.