Strength-mass scaling law governs mass distribution inside honey bee swarms

Abstract

To survive during colony reproduction, bees create dense clusters of thousands of suspended individuals. How does this swarm, which is orders of magnitude larger than the size of an individual, maintain mechanical stability? We hypothesize that the internal structure in the bulk of the swarm, about which there is little prior information, plays a key role in mechanical stability. Here, we provide the first-ever 3D reconstructions of the positions of the bees in the bulk of the swarm using x-ray computed tomography. We find that the mass of bees in a layer decreases with distance from the attachment surface. By quantifying the distribution of bees within swarms varying in size (made up of 4000–10,000 bees), we find that the same power law governs the smallest and largest swarms, with the weight supported by each layer scaling with the mass of each layer to the $$\approx 1.5$$ ≈ 1.5 power. This arrangement ensures that each layer exerts the same fraction of its total strength, and on average a bee supports a lower weight than its maximum grip strength. This illustrates the extension of the scaling law relating weight to strength of single organisms to the weight distribution within a superorganism made up of thousands of individuals.

Ontogeny of collective behaviour

“…In order to maintain their structural integrity as they grow, they must, therefore, adopt shapes that help distribute the weight of the structure over its different attachment points and over the individuals that it is composed of. There is preliminary evidence for the influence of this weight distribution problem [92], but how it translates from the behaviour of the individual workers remains to be determined.…”

“…These structures self-assemble fast enough that this process can be experimentally observed multiple times a day and progressively enough that it is possible to characterize their construction dynamics in detail. Recent studies have shown that they can be observed in three dimensions and experimentally manipulated in laboratory and semi-field conditions [92,165]. Finally, they have a clear beginning and end (these structures spontaneously assemble and disassemble throughout the day in natural conditions), which allows for the study of their complete ontogenetic arc.…”

“…For instance, CT scanning has been used to study the location of cells in developing embryos in three dimensions [189], as have immunohistochemical techniques to mark and trace subsets of individual cells [190]. Recently, the internal three-dimensional structure of living bivouacs [165] and bee clusters [92] has been described using CT scanning at different time points during the construction process. With this data, it is now possible to characterize the morphological development of certain forms of collective architecture and to look for potentially conserved structural organizations across different assemblages and species, analogous to the concept of the bauplan in ontogeny [191]; a shared behavioural skeleton shaping collective morphology.…”

“…Given enough computing power, it is even possible to accurately reconstruct the position of every individual in the structure, provided that they were not moving during the scanning process. This last point, however, illustrates a bottleneck with CT scanning and similar technologies: current affordable solutions that are adapted for observing large self-assemblages have a poor temporal resolution, making it practically impossible to track individuals over time [92,165]. Importing marking methods from embryology may somewhat help circumvent these limitations.…”

Honeybee flight dynamics and pair separation in windy conditions near the hive entrance

“…Experiments studying the social behavior and dynamics of honeybees mostly focus on activity at the hive entrance [15][16][17][18][19]. Studies that investigate swarms look at stationary collectives that are not in flight, such as work investigating the mechanical stability of honeybee swarms [20,21].…”