I went out to visit the bees a few minutes ago and saw an extreme example of some weird behavior. Hundreds of bees were all over the front of the hive moving up and down over and over.
This behavior is called washboarding because it looks like the bees are washing laundry on an old-fashioned washboard. Nobody knows why bees do this, but there are some clues that you can use to develop your own hypothesis.
It is generally a warm weather behavior. You won't find any of this going on when the temperature outside cool enough for long sleeves.
The bees do not add or remove anything from the surfaces where they are washboarding.
Only young bees participate.
Washboarding ceases during times when the hive is stressed.
The activity is centered around the main entrance to the hive. Some hives have more than one entrance, but the washboarding is around the one with the most activity.
When you look at a large group of washboarding bees on a dark, mottled surface (like tree bark) the surface appears to be shimmering or waving. I think this is because the bees near one another are often synchronized.
Washboarding is more likely to happen when the outside of the hive is rough, rather than smooth like glass.
Since the experts are stumped on the purpose of this behavior, I don't see any reason why you can't come up with an explanation. Use your imagination; what do you think they are doing?