Earlier this spring, I found about a dozen dead Carpenter Bees just outside of a hole that had been dug out the year before in one of the main struts of our deck.  There was also a dead bee that was just hanging from the hole!  What could have happened to them?  I don't have a problem with these bees - think they are pretty cool so did not want to disturb them.

sorry but no-one seems to know the answer to your question.