Dolerus niger

This would have keyed to niger using the RES key without too much difficulty had I not misread the first couplet. Having reached a dead end after the initial error I turned to Lacourt and there it keyed to niger. Returning to the RES key I then realised where I'd gone wrong. Unless I've overlooked it, neither key includes a diagram of the saw for this species, so I've not been able to confirm that fits, although it does help eliminate quite a lot of species.

male Dolerus nigratus showing head from front, wings, hind tibial spur, basal tergites, saw sheath and saw (2 photos), Wendling Beck Environment Project (Norfolk, UK), 9th June 2025