The forewings of this species are reddish brown with distinctive patterning towards the base; a black mark resembling the Hebrew letter nun (נ), thus inspiring the common name, with a pale cream-coloured area adjacent to this mark. The hindwings are cream coloured. "Setaceous" meaning having bristles, refers to the hairs on the top of the thorax and fringing the wings.
The wingspan is 35–45 mm. Forewing purplish grey or purplish fuscous with a leaden gloss; costal area at middle ochreous, merged with the bluntly triangular orbicular stigma: cell, a submedian basal blotch, and costal spot before apex purplish black; claviform stigma minute; reniform large, the lower lobe purplish; hindwing ochreous whitish, in female with the termen broadly fuscous.[1]
Lava pink with a broad dark brown subdorsal band. A lateral yellow band with a brown spot on it. Head reddish brown in color.[2]
The caterpillar of the species.
Hebrew letter nun - 15th-century Ashkenazi book-hand.
Two broods are produced each year and the adults are on the wing between May and October.[1] This moth flies at night and is attracted to light and sugar, as well as flowers such as Buddleia, ivy and ragwort.
The larva is pale brown red-brown or green with obscure paler dorsal and subdorsal lines and a broad pale ochreous spiracular line. It feeds on a huge variety of plants (see list below). The species overwinters as a larva.
^ The flight season refers to the British Isles. This may vary in other parts of the range.
^Seitz, A. Ed., 1914 Die Großschmetterlinge der Erde, Verlag Alfred Kernen, Stuttgart Band 3: Abt. 1, Die Großschmetterlinge des palaearktischen Faunengebietes, Die palaearktischen eulenartigen Nachtfalter, 1914
