Oncocera semirubella, the rosy-striped knot-horn, is a small moth of the family Pyralidae.
It is found in European regions, including the British Isles, and East Asia (e.g. China, Japan, South Korea and Taiwan).
The wingspan is 26âÂÂ30 mm. The forewings are light crimson or pink, sometimes much mixed with grey or dark grey, a whitish, greyish-ochreous, or grey costal streak; a broad ochreous-yellowish dorsal suffusion. Hindwings grey, slightly rosy-tinged. The larva is bronzy-blackish, with ten indistinct greenish lines; a whitish lateral spot on 3, including a black dot; head and plate of 2 black : amongst web on Lotus.
The adult moth flies in one generation by the end of June to August. It is easily disturbed on short grassland, flies from dusk onwards, and is attracted to light and sugar.
The larvae feed on bird's-foot trefoil (Lotus corniculatus), white clover, Ononis species, horseshoe vetch and Medicago species.