Fly

I agree with Martini, definitely a fly. If you look very closely, you can see two white dots just behind the thorax. These drumstick like structures are the haltares, evolved from the rear pair of wings and move in opposition to the front wings, acting like a vibration damping system. Only true flies have these. Dave

Based on the day of observation I would guess its a Christmas fly. Otherwise I think it looks like a robber fly, but a very small one. I think that flies are complex group but the eyes and short antennae look flyish to me. Flies also always have only two wings as yours seems to. http://www.projectnoah.org/spottings/10240628