I'm pretty certain this one is Stearibia nigriceps

In the full size image I think I see strong ocellars. The Manual of Nearctic Diptera chapter by J. F. McAlpine says Stearibia has weak ocellars.

They weren't visible in the smaller image. How can I access the full size?

Try now

Having looked more closely, I stand by L. varipes. The females are quite hard to tell from Prochyliza brevicornis, but the ocellars and postocellars of P. brevicornis are supposed to be weak, but "moderately strong" in L. varipes. It's hard to make out the setulae of the anepimeron, but I think I see a few on there (there can be as few as three).

The face is somewhat less yellow than the L. varipes I've encountered, but I don't see what else it could be.

I've thought about it some more, and I am not confident in my ID. If it's L. varipes, there should be substantial yellow on the frons and cheek, and it's just not there. I tried my best, but I don't know what this fly is. Better to leave it unclassified, I think. :(

to access full sized images. You obtain editor status by asking the publisher of the site John VanDyk whose contact info is at the borttom right of the page. Those with expertise such as yourself should have no problem gaining editor status. Thanks for looking at my fly.

Thanks for the info. I hardly feel like an expert, but as a grad student studying a few piophilid flies, I'm more familiar with their systematics than most! :)

...combined with the lack of postpronotals and the coloration of the head and legs are consistent with Liopiophila varipes. If the full size image of the ventral view (which I don't know how to access) shows setulae on the anepimeron, that confirms my ID, as Liopiophila is the only piophiline genus without a bare anepimeron.

and these were the only good shots I got.