Any clues please?

This was found today at Breney Common. Cornwall, it is a diverse site with shallow acidic pools and boggy ground as well as woodland and areas of more basic dry ground.

This was on some bamboo at the entrance, and the other species on it were mainly of wet woodland. it was the size of a large gall fly.

I have no idea where to start on this one but hope it is distinctive enough to get to species.