Longitarsus pratensis

My first attempt to key this seemed to go quite smoothly, with not much doubt at any couplet - but I ended up at Longitarsus curtus which was very unlikely to be correct (I don't think it's been recorded in Norfolk). I couldn't see where I'd gone wrong so checked the genitalia and, unsurprisingly, that swiftly eliminated curtus. With none of the couplets seeming ambiguous it was now a case of looking through the diagrams of the median lobes and trying to find a match. There were a few possible contenders but the best match was pratensis, and this was confirmed when checking against photos of the median lobes on Lech Borowiec's website. If I'd gone the other way on the final couplet I would have ended up at pratensis, so now I needed to work out why I'd gone wrong. It was down to the shape of antennal segment 8 - more elongate in curtus. Both are clearly illustrated in Duff and mine was, I thought, much closer to the illustration for curtus. The key doesn't specify what way to look at the antennae, but when I checked them again I realised they are not symmetrical. Looking at them from a different angle the 8th segment does indeed match pratensis. Lesson learned!

male Longitarsus pratensis showing antennae tips (from different angles), median lobe (flat and side views), front tarsus and elytra, Wendling Beck Environment Project (Norfolk, UK), 29th March 2023

I said after my first one, "lesson learned" - but apparently not. Okay, when this one also keyed to curtus at least I did then remember I'd had the same experience before. I think if you have to view the antennae from a specific angle, especially if that angle is not from above, then it would be really helpful if keys stated what angle you need to look at them from... This individual was 1.6mm long and came to light.

male Longitarsus pratensis showing hind tarsus and aedeagus, Cranwich Camp, 21st March 2025

Looking up my only previous record of pratensis I discovered from my notes that I had had the same issue then: I wrote, "A8 not as in Duff key but other characters agreed". Indeed the spermatheca is very different from that of curtus. (PS: if you saw a reference to luridus in a previous version of this page, that was an editing error and didn't actually relate to this insect).

female Longitarsus pratensis showing spermatheca, Tresidder (Cornwall, UK), 6th October 2020