Edit: Mollyblobs has identified this insect as a mayfly (Ephemeroptera). See her comment below. It is not an ichneumon wasp as I thought. Thank you Mollyblobs.
It is similar to the captured one that I blipped a few days ago. When this one was done posing for me it flew away. I managed several shots of it, some of which showed up the three-part tail better, and others had more detail in the head. The shiny dome is its right eye, which obscures the other eye and the head. I chose this one because of the wings, folded together so that they are not so transparent as the other one.
I liked the delicate pleating along the veins. There is also a small wing visible, which I hadn't noticed on the captured fly. Once again the body plus head measured about 10mm.
More detail in large.
Aided by a 10x magnifying filter