An immigrant from mainland Europe, appearing in southern England, and now resident in small numbers along the south coast. First recorded in Britain by John Langmaid at Southsea, Hampshire, on 9 July 2001. Steadily increasing in frequency throughout the first two decades of the 21st century, it is now accepted as likely to be a low-density breeding species in parts of Hampshire and Isle of Wight. Wingspan 34-40 mm. Very similar to
Lesser Broad-bordered Yellow Underwing N. janthe, from which separable in some cases only by dissection of genitalia. Set specimens of
N. janthina are separable by black outer border of hindwing, which on
N. janthe either stops before the costa or extends diffusely along it, while on
N. janthina, it is generally broader, and extends along costa without a gap, so the overall effect is of a black hindwing with a yellow spot. On underside of forewing of
N. janthe, the distal edge of black area is usually distinctly toothed. Larva feeds on various herbaceous plants. Some authorities dispute whether
janthina is a separate species, as there is evidence of hybridisation on the continent.