Here we go...
When the bees detect the pheromone left by the first hornet, they attack that hornet in a special way. They form a huge ball of bees that completely engulfs the much larger hornet. [See the photo at the left]
By vibrating their muscles, the bees raise the temperature inside this ball to close to 47°C, a temperature which the bees can survive, but the hornet can't. The high temperature inside the bee ball kills the hornet.
While a few of the bees may be killed by the hornet during this process, most survive, ensuring that the hive will not be attacked and destroyed.
Here is the site:
The Giant Asian Hornet ....................................