Wasps eavesdrop on rivals to assess their fighting abilities

Study provides further evidence of tiny-brained insects’ capacity for sophisticated behaviours

Wasps with brains a million times smaller than humans can spy on their rivals to assess their fighting abilities, according to a new study.

Scientists say the findings – based on observations of female paper wasps – provide further evidence of the insects’ capacity for sophisticated behaviours.

The experiment sought to challenge the idea that, compared to many vertebrate animals, insects were unable to use “social eavesdropping” to learn about potential rivals before interacting with them personally.

Researchers used enamel to mark reproductive females, known as foundresses, who form complex, linear dominance hierarchies based on the outcomes of fights with rivals. A wasp’s rank in the hierarchy determines its share of reproduction, work and food.

Two “fighter” wasps were then placed in a small container known as the fighting arena while two “bystander” wasps viewed the pair through clear plastic partitions.

Each fighter was awarded scores for aggressive behaviour such as biting, mounting, grappling and stinging.

Later the bystander wasps were put into the fighting arena either with a wasp they had observed or a fighter they had never seen before.

Biologist Dr Elizabeth Tibbetts and her students at the University of Michigan found that bystander wasps were more aggressive when paired with an individual which was the victim of lots of aggression in a previous bout, or that initiated very little aggression in the previous fight.

The researchers were also able to reject non-eavesdropping explanations for the observations, including phenomena called priming and winner/loser effects.

“The results show that P. fuscatus wasps use social eavesdropping,” said Dr Tibbetts. “Bystanders observe other individuals fight, and they use information about the fight to modulate subsequent behavior.”

It follows previous studies which showed paper wasps recognise individuals of their species by variations in their facial markings.

“It is surprising that wasps can observe and remember a complex network of social interactions between individuals without directly interacting with them,” said Dr Tibbetts.

“Complex social relationships are thought to favour the evolution of large brains and increased social intelligence, but paper wasp brains are relatively small.”