Social grooming has been known for a long time. Bees search each other’s fur and seem to clean each other. Whether this behaviour is used specifically to fight parasites has not been clarified.
It is a fact that in some colonies Varroa mites with massive injuries are found on the screen bottom board. Since the screen bottom board is protected from the bees by a grid and no other known inhabitant in the hives can be considered for the injuries, the injuries can only have been inflicted by bees outside the screen bottom board.
In the videos you can see that social grooming is usually triggered by cleaning and shaking movements of a bee that wants to free itself from pollen rests. Individual bees in the surrounding area then support the action.
But there are also real grooming bees. At least in some phases, they have made grooming their job. They check one bee after another and clean them.
I could only observe the social grooming and the often preceding shaking movements in summer and autumn. And only as long as there was pollen collected. This suggests the suspicion that this behaviour is exclusively due to the pollen remains in the bee fur.
Varroa mites with severe injuries are still on the control board. This suggests that social grooming has nothing to do with the mite injuries.
The following IR video was made in a tree hive:
See more videos here.