Alder Sawfly Eriocampa ovata

I found these fairly soon after finding my first couple of Eutomostethus ephippium, the similar sawfly that shares the overall appearance of red on the thorax and otherwise largely black body. That species has the red extending down the sides of the thorax, is much smaller (at least the specimen I compared was half the size) and has much less puncturing. Despite their similarity the two species are in different subfamilies.

There were four of these easily visible on a patch of low-growing (annually mowed?) riverside alder. Two are in the photos below - the first photo is one and the other three photos are the other.

Alder Sawfly Eriocampa ovata showing habitat, Bintree Mill (Norfolk, UK), 17th May 2023