Nemoura dubitans

The first few below were identified using the old RES key. Further down, the 2023 specimens were identified using the new FBA guide and the process seemed to be muuch more straightforward (though by no means easy). The shape of the pre-genital plate on sternite 7 is key but not always easy to assess. I've found it impossible to see the relevant detail on dry specimens so clear the abdomen in potassium hydroxide solution, though I have sometimes wondered if I have over-cleared it making the unsclerotised edges hard to discern.

On the first two I detached the end of the abdomen after sternite 7, which made it harder than necessary to view this (fortunately I did at least retain all of it).

female Nemoura dubitans showing abdomen tip (including close-up of one side) and sternite 7, Wendling Beck Project (Norfolk, UK), 11th April 2022

different female Nemoura dubitans showing abdomen tip and sternite 7, Wendling Beck Project (Norfolk, UK), 11th April 2022

On this one I did take a picture of the underside of its abdomen while it was still alive but it wasn't clear enough to see all the necessary details.

female Nemoura dubitans showing abdomen tip including sternite 7, North Elmham railway (Norfolk, UK), 9th April 2022

I haven't mastered how best to prepare these yet! Here I couldn't see the relevant details clearly enough without macerating the abdomen, but time I removed it from the potassium hydroxide before it was over-cleared. All the relevant features were clearly visible, but the dark shapes against a dark background didn't photograph well. So I then attempted to remove the gunk from inside the abdomen, but I again lost the definition of the edge of sternite 7 and the projection on sternite 9. This individual came to light (LEDs) - I think the first time I've had a stonefly attracted to light.

female Nemoura dubitans showing abdomen tip including sternite 7 (dry and cleared), Wendling Beck Project (Norfolk, UK), 1st May 2022

The following were identified using the FBA guide. Note that for the female I couldn't make out the details without first clearing the abdomen even though the specimen was freshly dead. I could just make out the epiproct prior to clearing but it was a great deal easier to see after clearing. The first male and the female were swept together from a piece of grass where I had seen one land.

female Nemoura dubitans showing pre-genital plate, Wendling Beck Project (Norfolk, UK), 29th April 2023

male Nemoura dubitans showing epiproct (in situ and detached for clarity), Wendling Beck Project (Norfolk, UK), 29th April 2023

These two weren't coupled when I caught them but soon made the most of each others' company in the pot.

same male and female Nemoura dubitans, Wendling Beck Project (Norfolk, UK), 29th April 2023

This male was netted in the same area as the last pair.

different male Nemoura dubitans showing forewing and epiproct (before and after clearing), Wendling Beck Project (Norfolk, UK), 29th April 2023

I struggled with this one, not entirely convinced at first that width of the pre-genital plate was sufficient for dubitans, and wondered if it might be avicularis. I did however figure that if it was avicularis, then probably so too were the females I had previously identified as dubitans (above). Eventually after checking all available references and examining photos of cleared abdomens (GBIF was useful for this) I was satisfied that I could rule out avicularis. One feature that isn't explicitly mentioned in any text but does appear in every diagram and photo that I have seen for avicualris is a three-pointed (sometimes it appears to be two-pointed) plate behind the apex of the pre-genital plate. In dubitans there is a small more square-shaped sclerite in this position.

female Nemoura dubitans showing abdomen before clearing (ventral and more-or-less caudal views) and after clearing (3 views, all ventral), Wendling Beck Project (Norfolk, UK), 25th April 2026