Social waves in Giant honeybees

This project investigates the phenomenon of `shimmering` which is a main component of the defense repertoire of the open-nesting South East Asian Giant honeybees. They occur in one-comb nests and prefer traditional nest sites such as trees, rocks or human buildings which they revisit over years and where they show aggregations of hundreds of colonies. Shimmering is a social waving pattern and displays a remarkable capacity of fast communication within a society, unique in the animal kingdom. Up to now, it is known that shimmering is evoked by visual stimuli of mainly predatory impact, in particular, by hovering wasps. It spreads as a wave-like, highly coordinated response over the whole nest within a fraction of a second. This aligns hundreds of colony members to flip their abdomens and distributes `information` about predatory stimuli in a giant honeybee nest. Shimmering has two potential addressees: first, the nest mates which are coordinated for participation, and which possibly get aroused or alarmed. Second, the potential predators such as wasps and mammals as external addressees, which are supposed to be confused, misguided and repelled by the dynamic visual cues produced by shimmering. In a first step, the project investigates the mechanisms behind `shimmering`, such as how it is generated, how waves are spread, which nest members are participating. A single-comb Giant honeybee nest has a roughly two- dimensional bee curtain as the main feature of the nest architecture. The bee curtain is made up by adult colony members forming a changeable and reactive super-organism. We suppose that the entity of curtain members continuously produce and receive information about the state of the colony reflecting its day-to-day business of foraging and reproduction, reorganization (e.g. periodic mass flight, preparation for reproduction and migration flights) or defensive actions such as shimmering. Therefore, we also investigate whether the bee curtain functions as a message board for incoming and outgoing information in visual, pheromonal and mechanoceptive pathways. In a second step, the project tests `ultimate` hypotheses to disclose the evolutionary principles how shimmering may benefit giant honeybees (`Why` has shimmering been evolved?). The research topic `shimmering` has relevance for a series of hot spots of the biology of social systems in general, in particular, for `cooperation` (e.g. `task partitioning`, `collective decision-making`), for `social communication`, and `social defense`. Shimmering relies on unique principles of `information transfer` and is a compelling example of `self organization`. Lastly, it will also address the issue of interdependencies between predator (in particular wasps) and giant honeybees as prey as part of a `co-evolutionary arms race`.

The project investigated collective organisation of the bee curtain of the nests of the Southeast Asian Giant honeybees (Apis dorsata), focusing on communication pathways that are unique in the realm of social animals. The main research topic was to analyse the defence traits of the shimmering behaviour by which hundreds or thousands of individual surface bees are synchronized and cascadized to flip their abdomens forming emergent Mexican-wave like patterns to propagate over the threatened side of the nest in a fraction of a second. These motion traits result from sophisticated group coordination, are based on sensory pathways in visual, mechanoceptive and olfactory modality, and guided by motivational factors such as arousal, alarm and threshold levels for cooperation and recruitment. One of the main findings of the project was that the visual patterns of shimmering repel predatory wasps from the nest. We further analysed the propagation properties of shimmering and assessed the motion elements of individual bees at the surface of Giant honeybee nests by stereoscopic imaging with a resolution (x,y,z) of 0.1 mm in time steps of 16.67 ms. This enabled us to identify two mechanisms, the bucket bridging and the saltatoric process, by which information is propagated across the nest within a fraction of a second. The benchmark velocity of bucket bridging was 0.3 m/s whereas the saltatoric processes speed up the wave by a factor of 3-4. We discussed the adaptive value of this speeding up the wave concerning the bottom-up attention in birds or mammals approaching the nest. In further experiments we investigated the modulation of the readiness of the colony for defence during the phases of mass flight activity which refurnish the functional architecture of the bee curtain up to six times per day. We detected for the first time vibrations at the centrally positioned comb which are provoked by the shimmering flashes; they are likely to establish channels for signalling information such of the defence state of the colony across the nest. We further measured the interrelations of free-flying wasps which scanned in front of the bee nest and the shimmering activities of the surface bees which were provoked by those. Shimmering has here the additional capacity to virtually wipe predatory wasps away from the nest area, which dramatically expands the repelling power of the collective which must have figured out concertedly fast the changing visual cues of the predators. Lastly, we measured by infrared-imaging how homoeothermy in the nest curtain is organized throughout the day focusing on active convection activities under warmer ambient temperature. The research topics are relevant to hot spots of social systems, in particular, to task partitioning, to collective decision-making, to social communication, and to social defence. Additionally, shimmering rely on widely unexplored principles of information transfer of arousal mechanisms such as recruitment or mobilization, and present extraordinary examples of social self organisation.