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How Japanese honeybees switch to 'hot defensive bee ball' mode when threatened

Japanese scientists have discovered a collective thought process behind the unique "hot defensive bee ball."
Japanese honey beeEnlarge
A bumble bee collects nectar from the calyx of a marguerite in Berlin on July 11, 2011. Like their relatives the honey bees, bumble bees feed on nectar and gather pollen to feed their young. (WOLFGANG KUMM/AFP/Getty Images)

Japanese scientists studying the unique "hot defensive bee ball" formed by Japanese honeybees to attack and kill their archenemy, the Asian giant hornet, have discovered a collective thought process behind it.

Scientists have known since 2005 that the honeybees, when threatened, will swarm around a hornet, forming a spherical bee ball and use their vibrating flight muscles to create heat, effectively cooking it.

Now researchers at Japan's University of Tokyo have figured out the "bee-brain mechanism" that regulates the thermo-balling behavior in Japanese honeybees but not in their relatives, the European honeybees, LiveScience reported.

Reuters quoted a University of Tokyo graduate student, Atsushi Ugajin, as saying: "When the hornet, the Japanese honeybee's natural enemy, enters a colony, the bees quickly form a 'hot defensive bee ball,' trapping the hornet inside and heating it up to 46 degrees C (115 F) with their collective body heat."

While the high temperature phase lasts about 20 minutes, it often takes up to an hour before the hornet dies inside the ball, he added.

To study the thinking behind the maneuvre, the researchers plucked individual bees from the bee ball at different times to see what parts of the brain were active.

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They found that cells in brain centers involved in complex behaviors were more active when in the hot ball than when the bees were carrying out other activities.

The scientists surmised that the bees' brain region was sending out directions to keep them producing steady heat hot enough to kill the hornets but not themselves.

"It might be that the neurons located in this area are also involved in processing thermal information in the worker honeybees," the researchers wrote in the paper, published March 14 in the journal PLoS ONE. 

Such neural activity wasn't seen in European honeybees. 

European honeybee hives, common in the US and Europe, are sitting ducks against the hornets, whch can grow to 2 inches, National Geographic wrote.

"These hornets go and rob honeybee colonies and the [European] bees have no chance. They can't sting through them. These hornets can bring down entire colonies," said Wulfi Gronenberg, a neuroscientist at the University of Arizona who was not involved in the study.

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