Analysis of the internal structure of honeybee swarms with x-ray CT

The western honey bee (Apis mellifera) is a domesticated pollinator famous for living in highly social colonies. In the spring, thousands of worker bees and a queen fly from their hive in search of a new home. They hang from a tree branch for several days, clinging on to one another and protecting the queen. We use x-ray computed tomography to investigate how honey bees structure their arrangement within the swarm such that the load on each bee is bearable, the bees do not fall down, and the swarm can adapt to the changing environment. We reconstruct the 3D structure of honey bee swarms ranging in size from 2,000 to 10,000 bees hanging from a flat board in the laboratory. The density of the bees is highest near the board and decreases toward the tip of the swarm, as the bees attached to the board have to support the most weight. We track individual bees in the swarm over time to find evidence of a mechanical division of labor. Most bees remain stationary, and a selected few move around within less dense areas of the swarm. Despite not having a clear leader, honey bees are able to organize into a swarm that protects the queen and remains stable until scout bees locate a new hive.