To Shimmer or Not to Shimmer: Collective Defensive Display in the Asian Giant Honeybee, Apis dorsata

Shimmering is a defensive behaviour exhibited by the open‐nesting Asian giant honeybee Apis dorsata . During shimmering, bees on the outermost layer of the colony flip their abdomens in a coordinated manner, creating wave‐like patterns that serve as an “I see you” signal to predators. Shimmering is triggered by a dark, moving object against a bright background, emphasising the role of contrast in initiating this behaviour. A. dorsata often constructs hives in visually heterogeneous habitats, such as tree canopies and thickets, or in human constructions, which can, in turn, interfere with the perception of approaching predators. Moreover, predators differ in the manner in which they approach A. dorsata colonies, from the saccadic flights of hornets to the swift approaches of bee‐eaters. Our study experimentally investigates how background patterns and stimulus movement (looming vs. lateral) influence shimmering behaviour. We used black‐and‐white chequered backgrounds of varying chequer sizes, while keeping the stimulus constant. Shimmering intensity reduced when the background pattern consisted of large chequer sizes, possibly because the stimulus was less discernible against this background. We then compared the shimmering response to a looming stimulus (akin to a bird predator's flight) and a laterally moving stimulus (akin to a hornet's flight). Bees responded to the laterally moving stimulus, but not to the looming stimulus. Furthermore, we examined how the movement of the stimulus within a restricted region in front of the hive affected the onset and intensity of shimmering. We found that shimmering was mostly initiated in the region proximal to the stimulus movement. By investigating the influence of both background heterogeneity and stimulus movement on shimmering, this study extends our understanding of this behaviour and demonstrates the effects of the visual habitat and predator motion on the shimmering response.