This is a male of Syritta pipiens, which is species introduced from Europe (there is a second species of this genus found in the US, but it is very rare).

This species is distinctive enough I think I'm safe in offering this identification:

I believe this is Syritta pipiens, a rather unusual syrphid. The odd form of the hind legs helps the males in fighting for dominance against other males. There are other species of Syritta, but not in our area.

The Syrphidae seems to be split between predators and eaters of decaying organic matter. This is in the latter group. They seem to be more common this time of the year in our area because the rains create more suitable habitat for the larvae, but I've seen them in the summer as well.

Here's one I photographed not too long ago:

for one example. for another. At least it's aplace to search while you wait for the answer from one of the dipterid experts.