@roger,
I haven't even noticed them - but I have never seen purple ones. Only like yellowish ones.
There was something I was reading about cicada killer wasps - it sounded like the holes descriptions we have. But like I said I been around them and stomped on the mounds and filled in the holes with ant and mosquito killer liquid and nothing came at me. And it was during the middle of the day. So they can't be all that aggressive.
anything I read about these critters via pest control product warn you that they are bad - but other places don't say anything bad about them more that they will only sting with provoked. I've never had a bad reaction (of course it hurts) but no allergies.
But there are more holes - it also says that each hole is probably just one wasp.