Deciding when to stand your ground and when to retreat can be a life-saving skill. One way to decide whether to pursue peace or combat is to know something about your rival and your own chances of victory. If you don't think you'll have the upper hand, it's better to conserve energy. This deliberation requires abstract social predictions – calculations that some people believe emerge only in larger brains. In a paper wasp species, however, previous work suggests that the wasps identify peers by unique facial markings to make social inferences about each other, suggesting that brain size might not be a limiting factor for social intelligence.

Recently, a team led by Elizabeth Tibbetts at the University of Michigan, USA, set out to test whether wasps inform social interactions just from watching others without any direct contact. Specifically, they wanted to learn if wasp aggression is predicted by the wasps’ observations. They set up a battle arena – a box where two queen wasps were placed in close quarters until they eventually came to blows. Meanwhile, other queens observed from outside through a clear divider. As the spectators watched the fight, the researchers monitored them and the fighters. The scientists then rated each combatant on an aggression scale based on how often the queens bit, grappled and attempted to sting, in addition to keeping track of how long the spectators observed.

Once the first round of combat was complete, one of the spectators was placed in its own battle arena with one of the queens that it had just watched fight. If the queen had been the aggressor in the previous fight, the spectator was less aggressive, while the spectator was more aggressive when presented with the loser from the preceding altercation. In order to determine whether the wasps are indeed making social inferences and adjusting their behaviour if they expect to win or lose, the team needed to rule out two alternative explanations: that watching a fight influences wasps to be more aggressive, like watching a violent movie, or that winners keep winning while losers continue to lose.

To test whether simply watching a fight primed the observer to be more aggressive, the spectator was matched against a stranger. If simply being a bystander at a previous contest increased the wasps’ aggression, the team reasoned that combatants who had previously been spectators would pick fights with any wasp that they were pitted against. However, some of the wasps were aggressive when set against an opponent, while others were not; just watching a fight did not inspire violence in the wasps. To test whether winning or losing previous fights dictates the outcome of future fights, the team set up two consecutive battles with different challengers. If the losers continued to suffer more defeats and winners vanquished their opponents again and again, fighting performance might not be a choice based on social inferences. However, the researchers did not see any relationship between how dominant a wasp was in one fight compared to the next; winners weren't always winners. In short, paper wasps learn about their peers and adapt their behavior in response to what they see.

What is more remarkable is that they pull off this feat with such small nervous systems. Even wasps decide when they can safely fight a foe with a weaker track record, or walk away to save energy and fight another day.


Wasps use social eavesdropping to learn about individual rivals
Curr. Biol.