bees stranded during robbing

[FRAMEshift]

I've seen this phenomenon several times.  When robbing breaks out in the beeyard, there are  lots of bees hovering and crawling over the surfaces of all the hives.  I generally shut down the hives to a one bee tunnel for a day or two and that helps to calm things down.  But there will be a cluster of bees outside the hive boxes hanging onto the open screened bottom boards. Maybe a thousand bees will spend the night clustered under each of the hives. The next day they will start flying around the hive again and that night they will cluster underneath again.

 I'm thinking these are robber bees from other hives.  I don't understand why they don't go to their home hive at night like all the other foragers do.  Or could they be foragers/robbers from the hive they are clustered on.  Maybe they passed their nectar through the screen (this is a normal practice) and then are not allowed back in the hive since they are not carrying food.

Has anyone else seen this behavior?  If so, do you do anything about it?

[Hemlock]

I've seen that.  We had a bit of robing excitement just recently.  Unfortunately the Screened Bottom Board was temporarily open at the time.  I had to wait two days for the clump of bees to leave so i could close it again.

I don't know whose bees they were. 
My guess is they are from that hive and they clump under the SBB because of the reduced entrance.  Then it takes a day or two for them to realize they can go back in the real way. 

Again...just a guess.