Brain secrets of bee ball assassins uncovered

Sandrine Ceurstemont, editor, New Scientist TV

Some animals use tricks to ward off predators but Japanese honeybees seem to prefer a more direct approach: they team up to form a ball around larva-stealing hornets and kill them with heat.

Now Takeo Kubo from the University of Tokyo in Japan and colleagues have uncovered the brain activity involved by collecting bees during the swarm behaviour. To simulate an invasion, they introduced a hornet on a wire to a hive. Worker bees quickly gathered around it to form a ball, vigorously vibrating their flight muscles to generate heat. An hour later, the hornet was cooked alive.

The team measured increased activity in a structure of the brain responsible for learning and memory in insects, called mushroom bodies. Interestingly, the same area was activated when the bees were exposed to 46??C heat in the lab, suggesting that the activity is triggered by temperature when the bees form a ball.

According to Kubo, the bees must maintain a very precise temperature in the ball. "If the temperature drops below 46??C, the hornet will not be killed, whereas if it's any hotter both the hornet and the bees will be killed," he says. The team thinks that the neural activity causes bees to modulate the movement of their flight muscles to maintain a constant level of heat.

Next, the team plans to examine differences between the sensory and motor systems of European and Japanese honeybees. The European variety, also present in Japan, doesn't form lethal bee balls. Giant hornets are predators native to Asia that resist being stung, suggesting that the behaviour evolved as an adaptation in Japanese bees.

If you enjoyed this video, watch sleepy bees slur their waggle dance moves or see bees headbutt their hive mates to warn them of danger.

Journal reference: PloS One, DOI: 10.1371/journal.pone.0032902

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