It only takes a few Asian hornets to wipe out tens of thousands of Japanese bumblebees. The bees' only defense is to incinerate scout hornets before they can come back with friends. The temperature inside the "bee ball" stays constant at 46 degrees C.
Japanese honeybees' response to a hive-invading giant hornet is efficient and dramatic; they form a "bee ball" around it, serving to cook and asphyxiate it.
Now, researchers in Japan have measured the brain activity of honeybees when they form this killer ball.
One highly active area of the bees' brains, they believe, allows them to generate the constant heat which is deadly for the hornet.
More info:
http://www.bbc.co.uk/nature/17381710