This species and Lesser Broad-bordered Yellow Underwing, Noctua janthe were only separated as different species in 1991. First recorded in Britain by John Langmaid at Southsea, Hampshire, on 9 July 2001.
Specimens of N. janthina (Lanmaid’s) can with care be determined by....
1/ Hindwing - The black outer border of the hindwing is generally broad, and extends along the costa without a gap, giving the overall effect of a black hindwing with a yellow spot.
2/ Forewing - The underside of the forewing should also be examined, janthe (Lesser Broad-bordered) showing a toothed outer edge to the black area that ends well before the outer edge of the wing. The outer edge of the black area in janthina (Langmaid’s) is usually smooth ending closer to the outer edge of the wing.
Separable in some cases only by dissection of genitalia.