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Paper wasps use eavesdropping to size up the competition

Paper wasps may have brains that are a million times smaller than ours, but they still have the capacity to learn, remember, and even make social deductions about others. A new study shows that paper wasps conduct a personal risk assessment by eavesdropping while other wasps are fighting. This allows the bees to evaluate the skills of their potential rivals.

Many animals, including some birds and fish, use “social eavesdropping” to minimize the personal costs of conflict. Until recently, this type of evaluation process was thought to be too mentally challenging for insects. However, a growing collection of evidence suggests that the tiny brains of insects are capable of deliberation. 

Study senior author Elizabeth Tibbetts is an assistant professor of Ecology and Evolutionary Biology at the University of Michigan.

“It is surprising that wasps can observe and remember a complex network of social interactions between individuals without directly interacting with them,” said Professor Tibbetts. “Complex social relationships are thought to favor the evolution of large brains and increased social intelligence, but paper wasp brains are relatively small.”

Paper wasp colonies are hierarchies that contain several reproductive females, or foundresses, that establish dominance and rank based on the outcome of fights. 

For their investigation, the researchers collected female paper wasps from sites around Ann Arbor, Michigan. In the lab, the wasps were marked with unique color patterns on the thorax. Two at a time, the “fighter” wasps were placed in a small container known as the fighting arena, and two “bystander” wasps were placed nearby to observe.

The fights were videotaped, and each fighter was scored based on an aggression index that awards points for behaviors like biting, mounting, and stinging. Bystanders were later paired in the fighting arena under one of two experimental conditions: either with a wasp they had observed or a fighter they had never seen before. The researchers compared the wasps’ behavior to establish the role of social eavesdropping.

The study revealed that bystander wasps were more aggressive when paired with an individual that was the victim of aggression in a previous fight. Bystanders were also more combative with individuals who they had observed behaving submissively.

Based on the comparison of the two experimental conditions, social eavesdropping was the only explanation for the observations.

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

Over the last decade, Professor Tibbetts was involved in previous studies which showed that paper wasps recognize individuals through their facial markings and behave more aggressively toward wasps they do not recognize.

Professor Tibbetts and colleagues also found that paper wasps have  long memories and behave based on previous social interactions.

The study is published in the journal Current Biology.

By Chrissy Sexton, Staff Writer


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