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Logical reasoning is complex behaviour, and has often been thought to be limited to animals that have complex nervous systems. But a new study shows that wasps can use a kind of logical deduction, the first such finding in invertebrates.

The type of reasoning is called transitive inference and it’s something people do easily: if you know that A is bigger than B, and B is bigger than C, then you can reason that A is bigger than C.

Elizabeth Tibbetts at the University of Michigan and her team put 40 paper wasps individually into a shallow rectangular container. These had a different colour at each end, and five colours were used in total, each corresponding to a letter from A to E.

In any combination, the colour that was linked to the later letter in the alphabet was rigged to give wasps an electric shock if they stood on it.

The wasps were first trained on letters that were adjacent to each other – A/B, B/C, C/D, and D/E. After 10 trials, they were then tested on pairs B/D and A/E, meaning they would have to use logic to avoid getting a shock.

Overall, 65 per cent of the wasps managed to correctly choose B over D, which is better than chance. They also chose A over E at around the same rate, but since A was always free of shocks and E always delivered them, that may be less significant, says Tibbetts.

Wasps may have evolved this ability because of their social structures. “They spend a huge amount of time fighting about dominant rank, and transitive inference is really important for figuring out dominance relationships,” says Tibbetts.

This type of study has been tried with honeybees, but they weren’t found to use the same deduction processes. Perhaps that’s because they don’t form these same dominance hierarchies, Tibbetts says.

Though the end behaviour may be similar, this reasoning may not work the same in wasps as it does in humans or other vertebrates. When humans make transitive inferences we use logic, but the further away from humans and apes we go, the harder it is to believe that they’re doing it in the same way we do, says Tibbetts.

“Insects frequently learn relatively quickly, but reach only modest – albeit highly significant and repeatable – levels of performance. The Polistes transitive inference learning performance patterns are very much in line with this common pattern,” says Sean O’Donnell at Drexel University in Pennsylvania.