Broom Dot Trifurcula immundella

Formerly given the vernacular name Broom Pigmy. Identification of adults requires examination of the genitalia.

This was the first Trifurcula that I have caught in my garden moth trap and its identity was suspected from its external appearance, but based more on the fact that I had previously found immundella nearby rather than any known differences from other Trifurcula species. The similar Scarce Broom Dot Trifurcula squamatella could conceivably occur here but currently is only known in Norfolk from the Brecks (per Norfolk Moths website). Other species of Trifurcula are available too although some are separable (from immundella/squamatella) on external characters and none have been recorded in Norfolk since the 19th century.

I have based this ID on images of female genitalia at the Moth Dissection website. The three images of immundella all show a sclerotised irregularly rounded piece in the narrow duct that enters (or exits from?) the side of the ductus bursae, which is not shown on the only image of female squamatella. Also immundella has two strips of reticulation down the sides of the corpus bursae which are not evident in the photo of squamatella, though this reticulation is faint (compared to the reticulation in some other Nepticulids) and I'm not completely certain that the quality of the squamatella photo is sufficient to be able to conclude that it is absent. Finally the apodomes of immundella are curved and joined by a round arch - based on the single image which isn't very clear, they seem to be longer and straighter on squamatella and the rounded join is not evident in the photo. In all of these respects, my moth is identical to the three immundella shown there, and different from the squamatella, and so my provisional conclusion was that this is sufficent to confirm the ID as immundella, but I really wanted to see some better photos and/or diagrams of the other species.

The Svenska fjärilar website came to the rescue. In fact there is some reticulation on squamatella, but the strips are broader and shorter. The closest species in terms of female genitalia seems to be cryptella but this seems to have a narrower ductus bursae and a narrower tip to the corpus bursae, and the reticulate strips end where the corpus bursae narrows (also on eurema).

There's no Broom growing in my little garden but it does grow in some close neighbours' gardens.

female Broom Dot Trifurcula immundella showing genitalia, North Elmham (Norfolk, UK), 25th August 2025

My previous one was a male, also found at light beside some Broom. There are more and better images of male Trifurcula genitalia at the Moth Dissection website including I think all of the British species.

female Broom Dot Trifurcula immundella showing genitalia, North Elmham (Norfolk, UK), 22nd August 2019