I went to check my bluebird house a little before sunset. (There is no nesting yet, but bluebirds have shown an interest. ) When I opened the door what I think was a bumble bee flew out. However, when I looked inside there was another bee almost pasted to the wall. I didn't want to disturb it as I'm allergic.

What was going on in there? A mating? A decision to build a nest? I left the door open so there really isn't a cavity there and into a picture. Any thoughts and information would be appreciated.