This species varies considerably in size (wingspan 37–43 mm) and colouration but is generally grey with three characteristic dark fascia across each forewing, giving it its common name. The hindwings are pale grey or buff. One or two broods are produced each year and the adults can be seen at any time from May to September. The species flies at night and is attracted to light.
The larva is also very variable, being green to reddish brown with alternating darker and lighter stripes. It feeds on various species of St John's wort. The species overwinters as a small larva.
^The flight season refers to the British Isles. This may vary in other parts of the range.