Okay.... now I'm perplexed. A few days ago I lamented about my hive losing all it's bees, wondering if they swarmed. Today, there's a lot of activity. Not as many bees as I saw two weeks ago, but at least hundreds around the entrance. They seem to be very agitated, with some bees attacking other bees and throwing them off the hive. Could this just be the girls getting rid of the guys? Cleaning house for winter? My bees protecting the hive from invaders? Or the invaders throwing my girls out?
Being from a warm area like yours I would not be sure but I would say that the boys may be gone by now. Do you still see drones? Are you by chance feeding them? The feeding could set up robbing. If you see much of this going on you might want to put a entrance reducer in place so they can guard it easier.
I see no drones and I am not feeding them. The upper super is fat with honey for the winter. After observing them again, seeing their agitation and fighting, I think it may be other invading bees. Do I just watch my girls lose their hard work or is there something I can do?
reduce the entrance so that they only have a small space to defend. that usually does it. if it doesn't, you can close the hive for a day and see if the invaders are discouraged. strong hives usually are fine if they can keep the entering robbers down to a bee or two at a time, it's when they are weak or there are to many/to large openings to cover that they get into trouble.
Close them off completely until after dark. Then put an entrance reducer on with the smallest hole. Do a search for "robber screen".
I had massive robbing a few days ago. I smoked them real good to break up the party and then reduced the entrance down to less than an inch. No more problem. You can still see an occasional invader trying to sneak in, but not a blitzkrieg like before.
http://www.bushfarms.com/beesrobbing.htm