Aaron,
 
Thank you for your thoughts.  I will check for Varroa immediately.  I had
treated for Varroa earlier, but I realize that doesn't guarantee anything.  I
agree that a collapse is likely, considering how little brood is in the hives.
 
I got another message from someone else who told me that he was
having the same  problem.  He commented that they have had unusually
wet weather where he lives--one day of sun followed by three days of
rain.  We are also having a very wet year, which seems to have caused
swarming in some of my other hives.  I wonder if the wet weather
somehow causes them to gather excess pollen or to store it in the brood
boxes.  Just a thought.
 
What was the weather like for you last year when your hives did this?