Angled Stem-sawfly Cephus spinipes

I recognised this in the field as being likely to be a Cephus species, and as soon as I examined the specimen I realised it resembled spinipes rather than the one I'd seen several times previously, pygmaeus. The antennal segments were all longer than wide, the tarsal claw bifurcation was short and almost perpendicular and (although it seems to be more a feature for females) the hind tibia were yellow apart from a dark apical ring. So in a way the ID was easy, but first I needed to make sure it certainly was Cephus and not one of the other genera in Cephidae (or even another family). ObsIdentify seemed to favour Calameuta pallipes. I didn't think it was, as photos online show a different abdomen pattern, but I needed to make sure - and that's where it became complicated.

Wright's key to genera shows what looks like a fairly obvious triangular hair patch on the 8th sternite for Cephus, which I could not make out at all on the dry specimen. It also says there's an apical row of large flattened setae best as dark hairs in side view - I could see some large dark flattened setae but I wasn't sure these were forming an apical row. The width of the head as described in the RES key and Lacourt seemed to confirm that it was Cephus but again referred to detail on sternite 8 that I couldn't make out. In the end I resorted to clearing the abdomen in potassium hydroxide and once I'd done that and isolated sternite 8 I could make out the triangle of thick black hair scales. This seems to be a much harder character to see than is suggested in Wright. I don't think any of my references show the aedeagus for Cephidae so I don't know if there are significant differences between the species, but as I'd cleared it anyway I've shown photos below in case they might be relevant.

male Angled Stem-sawfly Cephus spinipes base of antennae, tip of antenna, tarsal claws (2), hind tibia, tip of abdomen from side (with close-up of sternite 8), tip of abdomen from below, tip of abdomen from above, head from in front (with close-up showing measurements), sternite 8 after clearing, genital capsule and aedeagus from side, Wendling Beck Environment Project (Norfolk, UK), 9th June 2025