The rose sawfly is a Hymenopteran, not a fly. As the name suggests, it likes to lay its eggs on the stems of roses and let its larvae eat the leaves. The top photo show two of the very pretty larvae waving their bums in the air, characteristic for Argid sawfly larvae. The bottom photo shows the slit in the rose stem into which Mum inserted her ovipositor and laid her eggs. And bingo, here are the youngsters happily munching on the leaves!