Although a handful of Asian giant hornets can easily defeat the defenses of many individual honey bees, whose small stings cannot inflict much damage against such a large predator, the Japanese honey bee (Apis cerana japonica) possesses a collective defense against them.

When a hornet scout locates and approaches a Japanese honey bee hive it will emit specific pheromonal hunting signals. When the honey bees detect these pheromones, a hundred or so will gather near the entrance of the nest and keep it open, apparently to draw the hornet further into the hive or allow it to enter on its own. As the hornet enters the nest, a large mob of about five hundred honey bees surrounds it, completely covering it and preventing it from moving, and begin quickly vibrating their flight muscles. This has the effect of raising the temperature of the honey bee mass to 47 °C (117 °F). The honey bees can just about tolerate this temperature, but the hornet cannot survive more than 46 °C (115 °F), so it dies. Often several bees perish along with the intruder, but the death of the hornet scout prevents it from summoning reinforcements which would wipe out the colony.

http://www.amnation.com/vfr/archives/012026.html