I was thinking heat and the rocks might be a factor. Just pick up a house. Now’s the time they will be filling it up. Mason bees are 80% better pollinators than honey bees. No stinging. No hassle, lots of your garden gets pollinated.
I was gone today - all day - but I will look tomorrow and this weekend and see if there are any survivors. I’m assuming they should be out and about by now!
I will get a few of those Mason bee houses - or have Beau build me some. He loves it when I give him a project, LOL!