Although a handful of Asian giant hornets can easily defeat the defenses of honeybees, whose correspondingly small sting cannot inflict much damage against such a large predator as the giant hornet, the Japanese honeybee (Apis cerana japonica) has evolved an ingenious method of defending against the much larger predator.
When a hornet scout locates a Japanese honeybee hive and approaches the nest, the scout will emit specific pheromonal hunting signals. When the honeybees detect these pheromones, a hundred or so honeybees will gather near the entrance of the nest, apparently to draw the hornet further into the hive. As the hornet enters the nest, a large mob of about five hundred honeybees surround the hornet, 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 honeybee mass to 47 °C (117 °F). Though the honeybees can tolerate such a temperature, it is fatal to the intruder, which can handle a maximum temperature of about 45 °C (113 °F), and is effectively baked to death by the large mass of vibrating bees.
there's also a video on national geographic's site.