A couple years ago I got a mason bee observation hive for Christmas. It has been used on and off by some leafcutters, but last winter it really took a beating from the weather. It's started to get a little moldy and a colony of ants moved into the bottom 2 holes, so I figured it was probably done for as a bee house, but I left it up just for the fun of watching the ants. Then lo and behold, a couple of days ago I opened it up and a mason bee was sitting in one of the tubes! I checked again today and she was in there working on her nest and along with another bee! Apparently the mason bees don't care how it looks, and don't mind having ants as neighbors.