What makes huge honeybees wave?

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Giant honeybees flick their abdomens upward in synchrony to produce waves over their exposed nests, scaring off predators. A recent research explains shimmering’s causes.

Researchers reveal in the September Journal of Experimental Biology that bees shimmer most when presented a black item moving on a light backdrop under high ambient light. Researchers claim the experimental setting resembles hornets, one of bees’ major predators, flying against the bright sky to reveal what visual signals trigger the behaviour.

The behaviour “is intriguing as this is possibly one way in which a species of animal communicates with another to warn that they are capable of defending themselves,” says Neurobiologist Kavitha Kannan of the University of Konstanz in Germany, who was not involved in the research.

Tree branches and window ledges are common places for giant honeybees like Apis dorsata to build open nests. New research used two A. dorsata nests in roof rafters. The Indian Institute of Science Education and Research Thiruvananthapuram behavioural ecologist Sajesh Vijayan moved circular cardboard pieces of various sizes in grey and black on a grey or black backdrop near the hives. When black objects moved against grey backgrounds, the bees shimmered, but not when the contrast was switched.

In southern India, Sajesh believes the black-on-gray setting “resembles a natural predator or a natural condition,” which is likely why. “Open-nesting colonies are always exposed to a bright sky.”

The crew saw minimal shimmering at dawn and nightfall. Shimmering is a reaction to predators or other undesirable visitors, such as a bee from another colony, therefore the researchers assume additional protective behaviours may be at play under dark surroundings.
“We also think shimmering is a specialised response to hornets because it has not been reported in birds attacking or flying past these colonies,” Sajesh explains. Birds “elicit a mass stinging response.” Because approaching birds seem enormous in the bees’ visual range, they may decide, “Let’s not take any more chances, just sting,” Sajesh explains.

Shimmering disappeared in both hives when bees were shown the tiniest items, a four-centimeter circle. A minimal size threshold produces ripples, according to the findings.

Even after repeated exposure to the artificial setting, the bees’ shimmering power did not fade, maybe because it’s beneficial to keep attentive against persistent predators like hornets.

How the study bees see items is unknown. Sajesh explains, “They could be seeing this object moving, or they could just be responding to a visual field reduction.”

That question will be investigated by researchers. To determine what shapes and movements bees like, they are using LED displays to change backdrop colours, patterns, and item forms.