Appears to be cicada exit holes. Mystery solved.

At this time of year?

That is the big question. We had an almost springlike summer, coolest June thru October on file. I mowed the area flish to ground in mid August. The chimneys were not there then. Since Cicada emergence is temperature related, and we had only a small flush early on, I am wondering could it be that these three emerged late in the prefall temperatures, while others emerged earlier? There are seven holes in area.