Leuctra fusca

A widespread species that can be found flying quite late in the year.

This one was caught in a moth trap - I think the first time I've caught a stonefly that way. The abdomen was dry and curled when I examined it and I couldn't be quite sure which segments the processes were on. From the surface with the processes it looked like they were on neighbouring segments, but from the side it looked like there might be an additional segment in between (as in Leuctra nigra), so I macerated the abdomen in potassium hydroxide solution for a clearer (and straighter!) view.

male Leuctra fusca showing forewing and abdomen tip (two views from different orientations when dry and two views from the same orientation, one closer up, after maceration), Porthgwarra (Cornwall, UK), 19th October 2022

I found this one closer to home, resting on a leaf beside a dyke. The first couplet in the Macadam, Feeley & Doe key to the family Leuctridae separates Leuctra geniculata from all other British members of the family in having a whorl of outstanding hairs round the apex of each antennal segment (as does the RES key too). Now this specimen *did* have a whorl of outstanding hairs round the apex of each antennal segment, so is it geniculata? The hairs in the apical whorl are not quite as strong or numerous as shown in the diagram for geniculata and contrast less with the remainder of the hairs on each segment, these resembling those in the diagram for hippopus (as a representative of the other species). Moreover photos of Leuctra geniculata online show more obvious whirls of hairs and each segment is considerably shorter than on my specimen, and this is also clearly shown in the photo in Macadam, Feeley & Doe in the species section dealing with Leuctra geniculata. So I didn't think mine can be geniculata, and abdominal processes confirm this. Moving on past this slightly iffy antennal character it goes on to key smoothly to Leuctra fusca.

male Leuctra fuscashowing antennae (2 views) and abdomen tip (side and dorsal views), North Elmham railway (Norfolk, UK), 27th October 2023