Sorry, no picture at the moment. I have noticed numerous small mounds, rather like large earthworm castings, with about a quarter inch diameter hole down the center. They are turning up all over my yard. Watching closely, I have been able to spot something coming up the hole nearly to the top, but so far they stop and do not come out, or even come up far enough to give me a good look at what I expect will be their head.
I am thinking ground hornets are a possibility, but with so many individual holes, let us just say I hope not.
Possibly a ground dwelling bee?
I have only spent about five minutes watching and waiting. Probably just need to pull up a chair and wait them out.
Pretty sure they are not ants, holes are huge for ants, and not enough activity - I would expect to see an ant going in or out in the time I watched, not just holding station below the mouth of the hole.
Ooh, that reminds me of the year the 13-year cicadas came out when I was a kid not far from New Jersey. In the early spring, there were all these holes the size of a pencil stab mark into the ground. And then some time later the world filled with enormous and rather interesting, but waaaaay too numerous big bugs.
Works at a residential alternative high school in the Himalayas SECMOL.org . "Back home" is Cape Cod, E Coast USA.