European honeybees have no innate defense against the hornets, which can rapidly destroy their colonies. Although a handful of Asian giant hornets can easily defeat the uncoordinated defenses of a honeybee colony, the Japanese honeybee has an effective strategy. When a hornet scout locates and approaches a Japanese honeybee hive, she emits specific pheromonal hunting signals. When the Japanese honeybees detect these pheromones, a hundred or so gather near the entrance of the nest and set up a trap, keeping the entrance open. This permits the hornet to enter the hive. As the hornet enters, a mob of hundreds of bees surrounds it in a ball, completely covering it and preventing it from reacting effectively. The bees violently vibrate their flight muscles in much the same way as they do to heat the hive in cold conditions. This raises the temperature in the ball to the critical temperature of 46 °C (115 °F). In addition, the exertions of the honeybees raise the level of carbon dioxide (CO2) in the ball. At that concentration of CO2, they can tolerate up to 50 °C (122 °F), but the hornet cannot survive the combination of high a temperature and high carbon dioxide level. Some bees do die along with the intruder, much as happens when they attack other intruders with their stings, but by killing the hornet scout, they prevent it from summoning reinforcements that would wipe out the entire colony.
Source: Weird Facts