Like fans in a stadium, giant honeybees at their nest make big, rippling audience waves, new video shows.
And the bee waves are spooky enough to drive away predatory hornets, an international research team reports online September 10 in PLoS ONE.
Giant honeybees (Apis dorsata), unlike western honeybees, form open nests without outer coverings. Thousands of the giant bees cling to each other, sometimes seven layers deep, in a mass around the home comb, says Gerald Kastberger of the University of Graz in Austria.
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Wave patterns swirl across the outer layer of this mass as a sequence of bees tip their long abdomens up and down. Kastberger and his colleagues filmed and analyzed in detail some 450 bee waves, called shimmering, in two colonies on water towers in Nepal.
Moving bee patterns offer what Kastberger calls “a very modern problem” to study: self-organization. “It’s a question of organization of a team without a chief,” he says.
Smaller waves of a few bees break out as nest mates arrive and take off. When bee-hunting hornets buzz in, however, bees wave big. Seventy bees can flip into action in 600 milliseconds and hundreds of bees join in as the pattern swirls over the nest.
These big hornets hunt adult bees as food and can snag a forager out of the air. As hornets dive toward a massive bee nest, “they probably think it is a very nice supermarket where they can get everything without paying,” Kastberger says.
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Ripples of bee rears, though, change the hornet’s direction. At closer than 52 centimeters, the hunter veers away as the audience waves. The bees’ sudden motion may startle the predator, but whatever the mechanism, it works, Kastberger says. Waving maintains a rough no-hornet zone around the colony.
The new paper puts some data behind what observers have guessed, says Michael Breed of the University of Colorado at Boulder, who studies social insects. “To anybody who sits and watches these bees for any length of time, it’s clear the shimmering is happening when there’s a hornet around.”
“I have seen the same thing in Apis cerana [a smaller native bee species] in Japan,” says Randall Hepburn of RhodesUniversity in Grahamstown, South Africa. These Japanese bees also have to contend with killer hornets and have evolved a range of defenses. Both the Japanese bees and the giant honeybees can mob an invader and rev up their muscles to temperatures that cook a wasp but not a bee.
Western honeybees have not evolved with the big bee-hawking hornets of Asia and don’t shimmer, Breed says.
Besides the new paper’s descriptions of predator-prey dynamics, he welcomes details on bee wave-making. “One of the intriguing things,” he says, “is that it’s really pretty.”
Swirling waves sweep across the crowds of giant honeybees clinging to their nests.
Credit: Kastberger, Gerald et al. PloS ONE