Weight distribution in honey bee swarms

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 self-assemble into a swarm that hangs from a tree branch for several days while worker bees scout for a new hive location. How bees are arranged within the swarm to distribute forces and optimize internal conditions is, so far, not well understood, since the majority of bees are hidden within the swarm. We reconstruct the non-isotropic arrangement of worker bees inside swarms made up of 3000 - 10000 bees using x-ray computed tomography. We find that the structure of the swarm is non-homogeneous. Some bees form stationary layers  near the attachment board and scaffold-like chains throughout the swarm. The cross-sectional area of the swarm and packing density of bees within it distributes the weight such that the top layer of bees supports the most weight without overloading individual bees. The remaining bees use the chains as pathways to walk around the swarm, potentially to feed the queen or communicate with one another. This internal structure allows the swarm to protect the queen and adapt to the changing environment, and leaves scout bees free to investigate potential new hives.