蜂蜜影视 日本蜜蜂“热杀”马蜂(有配乐！）

The defence mechanism is known as a 'hot defensive bee ball'. 
When hornets attack, they kill all the worker bees, before 'looting' a nest for larvae and food. So the bees developed the defence mechanism to stop the predators. 
The bees swarm over the hornets in groups of up to 500, and start vibrating their wings until the temperature reaches 47 degrees centigrade. The heat is fatal for the hornets.