What’s a honey bee to do when a hornet comes poking their head where they’re not wanted? The outer shell of a hornet is too dense and thick for a honey bee to penetrate by stinging, so what can they do to defend themselves? Of course! Form a hot bee ball around the critter!
The bees will actually cluster around the invader in a tight spherical formation, engage their brains into “cooking mode” and actually bake that sucker into oblivion! They create heat by vibrating their wings and can actually get the center temperature of the ball up to 117 degrees Fahrenheit…enough to make toasted wasp. There is a slight debate as to whether the death is actually from the heat itself or from suffocation.
Scientists first noted this defensive behavior in 2005, and have been studying it since then. They have now figured out the bee-brain mechanism that regulates this behavior in Japanese honey bees, but not yet in their European counterparts. During bee ball defenses, random honey bees were plucked from the cluster and their brains were examined to see what parts were active. It was found that neurons in the brain center were far more active than when carrying out other activities. It’s theorized that the neurons in the brain’s center are involved in processing thermal information.
This same brain information was seen when the bees were exposed to heat, which supports the researchers’ theory that the bees were working to carefully regulate enough heat to kill the hornet, but not themselves. So far, this neural activity has only been isolated in Japanese honey bees.
In their research paper, the scientists stated, "Because there is only 3 to 5 C difference (5 to 9 degrees F) in the lethal temperature between the Japanese honeybee and the giant hornet, accurate monitoring and precise control of heat generation during forming a hot defensive bee ball seem critical for the Japanese honeybees.”