Langmaid's Yellow Underwing Noctua janthina

This species is increasing and spreading north, and is now regularly recorded from Norfolk. Identification is difficult and is complicated by frequent individuals that appear to be intermediate between Langmaid's and Lesser Broad-bordered Yellow Underwing Noctua janthe. "Textbook" examples show a yellow spot on the hindwing that is small and completely surrounded by black, whereas textbook Lesser Broad-bordered has a much larger yellow band, not bordered not separated from the whitish costal edge by any black at all. In reality many are intermediate so additional characters need to be checked. Perhaps the best character (although perhaps not failsafe) is on the underside of the forewing where the terminal edge of the dark base is smooth on Langmaid's and jagged or toothed on Lesser Broad-bordered. The colour beyond this tends to be more yellowish on Lesser Broad-bordered. Easier to view on a settled moth in a glass pot, but certainly not reliable, the pale costal edge of the forewing underside has a dark line through it at approximately two thirds - on Lesser Broad-borderd it tends to be similarly pale either side of this line whereas on Langmaid's it tends to be darker on the basal side of the line. However I have retained a number that suggested Langmaid's on this feature which proved to be Lesser Broad-bordered (or sometimes intermediate) on further examination.

Differences in male genitalia seem to me to be wholly unreliable. You need to evert the aedeagus, which isn't always easy, and the position/size of the diverticulum is supposed to be different. This can be hard to see in photos as this is a three-dimensional structure, but I have caught a number of individuals which I belive to be Lesser Broad-bordered Yellow Underwing that seemed to fit Langmaid's on this feature (and were very similar in this respect to the Langmaid's below).

It is not always be possible, based on current knowledge, to assign every intermediate example to one or other species without DNA analysis.

Having spent several years carefully examining scores of Lesser Broad-bordered Yellow Underwings, and sometimes finding promising candidates which, on closer inspection, did not stack up as convincing Langmaid's, I was hopeful that I might find a good Langmaid's when I visited Kent (where Langmaid's is much commoner than in Norfolk). The first was a bog standard Lesser Broad-borderd but the next immediately stuck out as being dark and proportionately shorter-winged (one wing was damaged but the good one looked short). The hindwing was very good - perhaps not perfect (as it wasn't completely surrounded, or at least only faintly so on one side) but very nearly so. The underside of the forewing (the one that wasn't damaged) was spot on for Langmaid's, unlike any of the Langmaid's candidates I have examined previously. The genitalia also matched Langmaid's, although as described above it has done for some examples I've previously caught that I consider to be Lesser Broad-bordered. This is certainly the best candidate I've ever had for Langmaid's, and taking the whole suite of characters into consideration I am happy to call it one.

male Langmaid's Yellow Underwing Noctua janthina showing uppersides of wings, undersides of wings, close-up of underside of tip of forewing, genitalia (2 views) and everted aedegus (three views), Cooper Street, near Ash (Kent, UK), 17th July 2026