Giant honeybees send waves rippling across their open nests by bending their abdomens upward in coordination, a sight that approaching predators tend to shy away from. A new study has revealed more information about what triggers the behavior, called shimmering.
Researchers describe the experimental setup showing bees a dark object moving against a light background under bright ambient light. The researchers argue that the researchers' sense of curiosity sets off the behavior.
Kavitha Kannan, a neurobiologist at the University of Konstanz in Germany, describes the behavior as "interesting as it is perhaps one way in which a species of animal communicates with another to warn that they are capable of defending themselves."
Apis dorsata is a giant honeybee that prefers to nest open nests hidden under tree branches and window ledges in places like trees and roof ledges. Circular cardboard pieces of different sizes were moved near the bees by behavioral ecologist Sajesh Vijayan against a gray or black background. The bees sparkled when a black object moved against the gray backdrop.
That's most likely because the black-on-gray setup "resembles a natural predator or a natural condition," according to Sajesh, who goes by his first name as is common in many parts of southern India. "These are open-nesting colonies, so they are always exposed to a bright sky."
During the dim twilight periods of dawn and dusk, the researchers observed little shimmering. Because shimmering is a reaction meant to be experienced by a predator or other undesirable visitor, such as a bee from another colony, the researchers speculate that other defensive behaviors might be at play.
“We also believe that shimmering is a specialized reaction toward hornets because it has not been seen in instances of birds attacking or flying past these colonies,” says Sajesh. That may be because approaching birds may loom large in the bees' visual field, and their attitude may be “let's not take any more chances,” according to Sajesh.
When bees were presented with the smallest objects, in this case a circle four centimeters in diameter, the sparkles completely vanished. The conclusion suggests that there is a minimum size threshold that triggers the ripples.
Even when bees were exposed to the artificial setup repeatedly, the shimmering power did not fade, perhaps because it's advantageous to remain vigilant against predators like hornets that make long-lasting strikes.
The exact manner in which bees perceive the objects in the study is not known yet. “They could be seeing this object moving, or they might be reacting to a decrease in their visual field,” Sajesh says.
The researchers intend to further investigate this possibility. They are also experimenting with LED screens to modify the background colors, patterns, and object shapes in order to see which shapes and motions may be beneficial to bees.