Sawfly

A black and yellow sawfly, probably Macrophya monatana (Hymenoptera: Tenthredinidae).

Photos taken in the field below Chazey Wood, near Caversham, UK, on 2011-05-09.

Update on Sun 2011-06-05 by Tristram Brelstaff

This is a female; the males of Macrophya montana are almost all black.