I had a bunch of either mason or carpenter bees in my tumbler last year. I stopped using it and just stuck with the 3-bin piles. I need to dump the tumblers out. I decided to disassemble them since I prefer the capacity of the 3-bin system.Today I found a swarm of bees in one of my compost bins. I propped open the lid so they'd find it less hospitable, and it looks like they are gone. Too bad I don't want to start a hive right now!