What is it?
No interactions present.
A check on the NatureSpot site suggests two candidates: (i) the Alder Sawfly (Eriocampa ovata) and (ii)Eutomostethus ephippium - found on grassy places. Where you observed the sawfly might help decide between these possibilities.
I've got good pictures of one of these, but gave up when two experts completely disagreed with each other. I hope you have better luck
latest pics and diptera videos
Lat/Lng: 54.983, -1.745
OS grid ref: NZ164654
Beside amphibian pond. Grasses, wild flowers,young trees and the river Wear one hundred yards to the south.