I saw this bee fly tonight. It looks similar to a species that I have photographed in the past. Bombylius major, but I don’t think this is that species–there is not a clear distinction between the clear and the brown color on the wings, and the behavior seemed different–this one preferring prairie flowers, B. major seeming more attracted to leaf-covered ground.
I think this is a male because the eyes meet in the middle of the head, and on females the eyes are smaller and don’t meet (at least, that seems to be how it works in B. major.)