i'll try to get a picture of one but i think that is what they are. i shoved a toothpick all the way in on one hole. i'm replacing the posts with treated fir. heavy dry paint doesn't even stop them
As for the term benign, they are far more docile neighbors than hornets and wasps who will chase you for 100's of yards if you mess with them. These guys won't bother. So yes, that is a relative description.
Treated fir may stop them for you but, I haven't had success with it.
I also have not as yet been stung by one. And I battle them most any time I am out on my back porch. So my comment is based on experience. And that experience is done with great caution because I am violently allergic. EPI pen in hand before I go into battle. Weapons of choice, Fly swatter will knock males out of the air. Females get AA,; anti aircraft from a can of Hornet spray.
My Back porch has a 24 foot span triple 2X12's treated fir with CDX plywood spacers, I would hate to have to rebuild it. The eaves and rake boards on my house are all 2" X 8" Western Cedar. They love it.
I feel like Berlin Germany at the end of WWII. What little ammo I got to stop the air raid bombing ain't enough.
All that said, the size you stated 1/4" is for a smaller bee. I'm talking about what is known as Bumble bees in size.
The smaller wood bee looks like a small housefly but stings like a wasp. In hordes. Mean little Bastards, tough to mess with so avoid the encounter. Spray from a distance with any Hornet spray. And plan to run like hell.
When you remove to replace the post, if they are still alive, you'll understand why I said run.