Leaf cutter bees need smaller holes than the Mason bees. A Leaf cutter bee laid eggs in one of my Mason bee tubes. I got a block of Leaf Cutter bees for $10 shipped and was late in setting them out.
While checking my Mason bee tubes, a bunch of Leaf Cutter eggs were in one tube and fell out onto the ground when I pulled the paper tube out. I was changing out the old tubes used last year with new paper inserts.
You can see the eggs in the tube located four rows down from the top and the first hole. The hole is not completely sealed off.