I thought these were Andrenids, and then realized they were Nomada--I had been puzzled that none of them seemed to be carrying pollen (Nomada are parasitic on Andrenids). Funny, there were only a few of the fuzzy yellow-and-black Andrena around, presumably the ones that dug the holes, and I could not get a photo. Also hovering around was a Bombylius pygmaeus, laying eggs (Flickr photo), and a Mutilid.

Presumed to be female--was entering Andrenid nests, presumably to lay eggs.

I'm linking several photos here, even though they were not all the same individual, in order to keep them together, in hopes of an ID. I think I'll go back to this colony and collect a few--it is right next to a sidewalk in a lawn.

Hmm. Looks a bit like this one, identified as Nomada imbricata:

(John agrees with this in comments!) Other individuals from the same colony, presumably the same species:


An associated Andrena, the presumed host species, photographed in the same "colony" two years later: