a sawfly larva (Pristiphora)

a sawfly larva (Pristiphora)

Observation - a sawfly larva (Pristiphora) - UK and Ireland. Description: A sawfly larva ... but which one? I thought that the brown head and lack of black spots should make this one fairly easy to identify but I've not been able to find it. On Birch. Edit: Changed to match Martin's ID. Many thanks.

A sawfly larva ... but which one? I thought that the brown head and lack of black spots should make this one fairly easy to identify but I've not been able to find it. On Birch.
Edit: Changed to match Martin's ID. Many thanks.