Tenthredo arcuata

I have really struggled to identify some of the yellow and black Tenthredo species - they frequently seem to show characters that aren't fully consistent with the available keys and I've had to leave a few unidentified. While identifying a recent arcuata I compared the saw with my photos of the saw of one of my previous records of arcuata and they are clearly different - I now think the older one was in fact brevicornis. Judging from the scape and fore femur detail I think at least one and probably three of my other older records of arcuata were also likely to have been brevicornis.

This is my recent arcuata, found on a buttercup. It keyed to arcuata and then I checked the saw and the shape of the teeth appear to be consistent with arcuata.

female Tenthredo arcuata showing face, hind tibial spurs and saw, Wendling Beck Environment Project (Norfolk, UK), 17th May 2024

The saw of the one above was clearly different to the saw of one I had previously identified as arcuata. In fact the previous one's saw appears to be spot on for brevicornis and it also had a black scape which would support that ID. There was a black stripe along the fore femur but this was narrow and not visible at all in the photo taken from directly above. The black scape and narrow black stripe on the fore femur invisible from above are shared by one or two others that I had previously identified as arcuata, so I now think those were also brevicornis. However some of my older records of arcuata look good. This one for example has an extensively yellow scape and the black line on the fore femur is much thicker and clearly visible from above.

female Tenthredo arcuata, North Elmham Cathedral Meadows (Norfolk, UK), 28th May 2018

Likewise I don't see any reason to think this next one was wrong. It also has an extensively yellow scape and the black line on the fore femur is much thicker and clearly visible from above.

female Tenthredo arcuata, North Elmham Cathedral Meadows (Norfolk, UK), 3rd June 2018

Thso one also has an extensively yellow scape and is extensively black on the side of the fore femur, the black being clearly visible from above.

Tenthredo arcuata, North Elmham Cathedral Meadows (Norfolk, UK), 23rd August 2021

See my Tenthredo brevicornis page for the ones that previously featured here but which I now think are more likely to have been Tenthredo brevicornis.

This one was on an Ox-eye Daisy and identified shortly after I processed the one at the top of the page. It keyed to arcuata relatively easily and the saw teeth match. I've not generally been very good at understanding the differences in the shape of the hypopygium, or at least applying them to specimens, but I managed to get some photos of it at least this time before damaging it too severely.

female Tenthredo arcuata showing saw (2 views) and hypopygium (in situ before clearing and isoalated after clearing) , Wendling Beck Environment Project (Norfolk, UK), 5th June 2024