The absence of the queen's pheromones makes worker bees abandon their normal role of policing the colony's reproductive behaviour, making the colony more vulnerable to parasitic bees from other colonies.

Before their colony collapses, worker bees have lots of sex, in a last ditch attempt to raise a final generation of males, as well as the offspring of intruder bees.

Associate Professor Benjamin Oldroyd, an Australian bee geneticist from the University of Sydney and Thai colleagues looked at what happened when a colony of Asian dwarf red honeybees (Apis florea) loses its queen.

They found the proportion of non-native (or parasitic) workers in the colony more than doubled. Almost half of the parasitic bees had active ovaries, compared with around one in five of the native workers.

"Worker policing is essential for maintaining reproductive harmony and, we now think, defending the colony against parasitic bees from other colonies. But to have some chance at immortality when the queen dies they are compelled to switch off their worker policing in order to lay their own eggs," says Oldroyd.

"The results of this study revolutionises our ideas about social insect colonies. They can no longer be thought of as a Shakespearean paradigm of a queen and her workers toiling away in harmony," Oldroyd says.

"The colony is a very delicately balanced society that only works because of the worker policing behaviour. Once the policing behaviour is switched off it all goes awry."

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