How do bees kill hornets with heat?
Short answerTrue
Asian honey bees engulf a hornet in a ball of workers and raise the temperature inside it. The bees can survive that temperature and the hornet cannot, and rising carbon dioxide inside the ball contributes to the effect.
How it works
A hornet scouting a nest is surrounded by workers who pile onto it in a tight ball and vibrate their flight muscles. The temperature inside the ball rises to a level the bees tolerate and the hornet does not. Carbon dioxide concentration inside the ball rises too, and lowers the temperature at which the hornet succumbs.
The margin is narrow. It works because the defenders' upper thermal limit is a little higher than the attacker's — a small physiological difference exploited by a collective behaviour, killing something no individual bee could handle.
Which bees, and why it matters
It is a defence of Apis cerana, which shares a long evolutionary history with the hornets that attack it. Apis mellifera did not evolve alongside those predators and defends far less effectively, which is a large part of why the arrival of Vespa velutina in regions where European honey bees are kept is a serious problem rather than a curiosity.
Sources
- The Biology of the Honey Bee — Harvard University Press (1987) · Textbook
- Asian Honey Bees: Biology, Conservation, and Human Interactions — Harvard University Press (2006) · Monograph
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