Allogrooming, social grooming of honeybees
During social grooming (allogrooming) 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.
Varroa mites with fatal injuries on the screen bottom board
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.
Conclusions from IR videos in the beehive
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 (or parasites?). Individual bees in the surrounding area then support the action. The shaking and cleaning movements that lead to allogrooming are described by Land/Seeley as a grooming invitation dance.
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 is not the only cause of mite injuries.