Paper wasps eavesdrop on fighting rivals to rapidly assess potential opponents without personal risk. This new finding adds to mounting evidence that even mini-brained insects have an impressive capacity to learn, remember and make social deductions about others.

Many vertebrate animals – including some birds and fish and numerous primates – minimize the costs of conflict by using “social eavesdropping” to learn about the fighting ability of potential rivals before interacting with them personally.

Keeping track of a network of individually differentiated social relationships is thought to be cognitively challenging and, until recently, was considered to be beyond the reach of lowly insects like paper wasps, which have brains a million times smaller than the human brain.

But a growing body of evidence suggests that the miniature nervous systems of insects do not limit sophisticated behaviors. The capacity for complex insect behavior may be shaped more by social environment than brain size, according to University of Michigan biologist Elizabeth Tibbetts, senior author of a paper published June 25, 2020 in the journal Current Biology.

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

In the study, Tibbetts and her students collected female Polistes fuscatus paper wasps from sites around Ann Arbor, Michigan, in the early spring.

Unlike a honeybee colony—which has a single queen and multiple equally ranked female workers—paper wasp colonies contain several reproductive females called foundresses. These females battle their rivals and form complex, linear dominance hierarchies based on the outcomes of those fights. A wasp’s rank in the hierarchy determines its share of reproduction, work and food.

In the laboratory, the researchers used enamel to mark all foundresses with unique color patterns on the thorax. Then, two at a time, “fighter” wasps were placed in a small container known as the fighting arena while two “bystander” wasps observed the pair through clear plastic partitions.

Coauthors include U-M EEB undergraduates Ellery Wong and Sarah Bonello, who have graduated. Wong is currently a United Nations intern in New York City and Bonello is joining the Yale Forestry and Environmental Studies graduate program.  

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The research is receiving widespread media attention including in Cosmos and an upcoming interview in early July on Michigan Radio's Stateside.