Cyprian honeybees will swarm together around a threatening hornet, forming a tightly-packed ball that kills the would-be-invader, but exactly how this happened was unknown. Now – by a process of elimination – a study suggests that the honeybees kill by depriving their enemy of oxygen.
Hornets are particularly nasty predators and will chop off the head of a bee before carrying it back to their nest to eat. Often greedy hornets will go so far as to invade the honeybee hive to obtain food such as larvae. "They can slaughter whole colonies in a few hours," says Alexandros Papachristoforou of the Aristotle University of Thessaloniki in Greece.