Honey bees understand the numerical concept of zero, demonstrating a level of cognition not previously known to exist in invertebrates.

A new study published in the journal Science finds that bees perform at a level consistent with non-human primates in recognising that zero is lower than one, despite bee brains being much smaller and simpler.

So far, only a small portion of the animal kingdom has been shown to grasp the idea of zero. With the honey bee now joining the ranks of chimpanzees, Rhesus monkeys, vervet monkeys and African grey parrots, the obvious question is: how many other species can do this?

“Doing such complex tasks with such tiny brains suggests that higher animals and other vertebrates probably can do similar things,” says Adrian Dyer from RMIT University in Melbourne, Australia, co-author of a research team led by PhD student Scarlett Howard.

“The study opens the door to what we think cognition is.”

In a series of laboratory experiments, scientists used pairs of black-and-white images to train honeybees (from the genus Apis) to understand the concepts of ‘greater than’ and ‘less than’. When a blank image was introduced — representing zero — the bees were able to correctly identify that it sat at the lowest end of the number continuum.

Moreover, the bees were even more accurate when comparing pairs of numbers that were further apart (zero versus six, for instance) than pairs that were closer together (zero versus one). This ordered number effect is also observed in humans.

The bees’ numeric processing abilities are thought to have evolved as a consequence of living in complex environments. Recognising nectar-rich flowers, situating them in time and space, and communicating their location to other members of the hive — all of these tasks may have pushed the bee brain to evolve equally complex processing solutions.

The discovery of zero numerosity in honeybees may also help scientists unravel the cognitive mechanisms responsible for numeric processing. Recent work has found that crows and mammals process numbers using different brain structures, suggesting that the ability evolved independently in each group.

“This study gives us another model to look at how the brain processes the concept of zero,” explains Dyer.

“Directly measuring brain responses is often more accessible in an insect than in a vertebrate.”

For humans, understanding the concept of zero is a relatively recent evolutionary feat. Zero first appeared in written form around 2,000 years ago, and there is no signifier for it in the Roman numeral system.

Future computer programmers could learn from the honeybee model of cognition, notes Dyer.

“Looking at animal brains gives us different models of information processing that can be incorporated into future designs of computer processors, robots and artificial intelligence,” he says.