Eutomostethus ephippium

This specices is similar to Alder Sawfly Eriocampa ovata but has the red extending down the sides of the thorax, is smoother (less punctured) and smaller. Despite their similarity they are in different subfamilies.

This was found on Garlic Mustard in damp woodland.

Eutomostethus ephippium, Wendling Beck Environment Project (Norfolk, UK), 29th April 2023

This was found resting on a stem alongside a footpath in the same woodland as the one above. It proved to be a real headache to identify but in the end it seems it's the black form, var. nigrans, of Eutomostethus ephippium, which was once considered to be a distinct species, Eutomostethus nigrans but now regarded as simply a variety of ephippium.

I had several problems keying it. Firstly the spurs on the hindleg were clearly unequal, which accordng to Wright is wrong for Tenthredinidae and points to Xiphydriidae or Siricidae. I've had that problem before so didn't initially waste too much time with it, but when I got stuck later went back to recheck I hadn't messed up the family. Lacourt differentiates these on the number of spurs on the fore tibia - two on Tenthredinidae and only one on the others. On my specimen the first fore tibia I checked only had one spur, but one must have broken off as the other had two.

The next place I struggled using both Wright and Lacourt was interpreting the straightness of the subcostal vein. It turned out I had to take the "straight" option but in reality it does dip slightly, albeit not strongly. My next problem using Wright's genus key to subfamily Blennocampinae was interpreting the fork (or otherwise) of vein A3. I couldn't see enough of the vein on the wing I'd removed to view flat so checked the other wing. Despite taking care I still managed to split this between the anal cell and vein A3 but the vein itself wasn't damaged. It wasn't as clearly forked as shown in the diagram but there was a short projection towards the costa where the vein recurved, so I took this to be forked. Lacourt agreed that the vein shouldn't be forked but adds criteria regarding the length of the antennae and relative length of segments 3-5. Segment 3 was clearly longer than 4 or 5 so it seems that the costal projection on vein A3 doesn't count as a fork...

female Eutomostethus ephippium var. nigrans showing right wings, left forewing vein A3, hind tarsal claws, face, abodomen from side and epicnemial groove, Wendling Beck Environment Project (Norfolk, UK), 5th June 2024

This one was swept from nettles.

Eutomostethus ephippium, Pensthorpe (Norfolk, UK), 15th May 2023