We keep finding these little “buzzbombs” in our basement. Almost every day there is a new one trying to wreck the place. I think they might be some kind of ground bee, but I’m not sure. I can’t find anything quite like them on your site. They look like Tachinid flies, but their head is much smaller and located underneath their body instead of at the front. He’s an incredibly ungraceful flier, and spends most of his time in the house trying to get off his back. I cooled him down in the refrigerator to photograph him, and to warm up, he would buzz like a jet engine winding up. They are some of the strangest flies I’ve ever seen in Colorado. Thanks for your time.
Interestingly, it seems like you arrived at the correct answer when you wrote: “… flies, but their head is much smaller … .” This looks to us like a Small Headed Fly in the family Acroceridae, and of the photos on BugGuide, it looks closest to Pterodontia flavipes or another member of the genus. We will try to contact Eric Eaton to get another opinion.
Yes, it is indeed a small-headed fly! Great call! Not sure of the genus, though. As larvae they are parasitic on spiders.