Democratic bees handle a menace.

[Intractable]

3. What you are seeing is the bees killing the hornet by raising its body temperature beyond what it can tolerate.

From Google ...

Bees kill hornets by forming a "bee ball" around the hornet and heating it to a lethal temperature. This defense mechanism is called "hot defensive bee balling".

How it works

When a hornet attacks a hive, hundreds of worker bees swarm the hornet.

The bees vibrate their wing muscles, which generates heat.
The bees also produce carbon dioxide.
The hornet is trapped in the center of the ball, where the heat and carbon dioxide build up.
The hornet is cooked and suffocated to death.

How effective is it?

The heat inside the ball can reach up to 46°C, which is hot enough to kill a hornet.
The bees can maintain this temperature for over 30 minutes.
The bees have a higher tolerance to heat than the hornets.

How important is it to deploy quickly?

If the bees don't deploy the ball quickly enough, the hornet will release pheromones that attract more hornets.

What is the evolutionary significance?

The relationship between honey bees and hornets is an example of an evolutionary arms race, where each species adapts to counter the other.