Paper wasps seem to be able to use logic, according to a new study at the University of Michigan. They are the first invertebrates known to be able to use the form of reasoning known as ‘transitive interference’, raising questions about how complex behaviour can arise even in minuscule brains.
A common example of transitive inference is the ability to understand rankings. So, if A is greater than B and B is greater than C, then transitive inference concludes that A is greater than C. This form of logic was originally thought to be present only in humans, though it has since been found in monkeys, birds, and fish.
To test for this ability, the researchers, led by evolutionary biologist Professor Elizabeth
Tibbetts, placed each wasp in an arena with an electrified floor which gave them a gentle electric shock. In the arena, the wasp was presented with two colours, one of which had a ‘safe zone’ in front of it where the wasp could escape the electric shock.
The colour pairs formed a hierarchy, with the safe zone in front of the higher-ranking colour. So, when colour A was compared with colour B, colour A had the safe zone, but when colour B was compared with colour C, the safe zone was in front of colour B.
Once the wasps had learned these pairs, they were then presented with unknown pairs, such as colour B and colour D. The wasps could accurately identify which colour had the higher ranking.
Paper wasps, which make their nests using dried wood and plant stem fibres mixed with saliva to make a papery substance, have a complex social structure which the team believes helped them to grasp the logic.
Previous studies found that honey bees, which have a nervous system around the same size as paper wasps, are not capable of using transitive inference. Unlike honey bee colonies, which have a single fertile queen and many other females of the same rank, paper wasp colonies have several fertile ‘foundresses’ in a linear hierarchy.
Since the hierarchy affects not only access to food but also work and reproduction, the team believes that paper wasps developed the ability to use transitive inference so that they can quickly and accurately assess new social relationships.
Paper wasps have brains smaller than a grain of rice. It is commonly believed
that the size of the nervous system determines whether an animal can use sophisticated
“Our findings suggest that the capacity for complex behaviour may be shaped by the
social environment in which behaviours are beneficial, rather than being strictly limited by brain size,” said Tibbetts.