Honey bees may have small brains – containing fewer than a million neurons compared to our 86 billion – but that doesn’t mean they aren’t capable of sophisticated thought. Past research has indicated that the insects can make collective decisions, communicate complex information to one another, interpret patterns, and even navigate to and from their colonies by counting landmarks.

And according to a new investigation published in Science, we can also add them to the very short list of animals that understand the abstract notion of zero.

"Zero is a difficult concept to understand and a mathematical skill that doesn't come easily – it takes children a few years to learn," said study leader Adrian Dyer, of RMIT University, Melbourne, in a statement. In their paper, Dyer and his colleagues explain how the ‘discovery’ of zero by ancient human societies, and its subsequent integration into their mathematical systems, was a critical step forward in our intellectual evolution.

"We've long believed only humans had the intelligence to get the concept, but recent research has shown monkeys and birds have the brains for it as well. What we haven't known – until now – is whether insects can also understand zero."

To test the bees’ capability, the Australian research unit set up a rather ingenious experiment. First author Scarlett Howard began by luring individual members of a bee group to a wall where several paper cards were hanging. Through repetition, she trained them to understand that a sugar water meal would be located under the card bearing the fewest symbols – a feat that is within their known cognitive ability. 

"They could come and see two circles versus three circles, or four triangles versus one triangle, or something like that,” Howard told NPR.

After they had mastered that task by consistently flying toward the card with the least symbols, Howard added a blank card into the mix.

The team was amazed to observe that although the bees often picked incorrectly, they chose the empty card over cards with varying numbers of symbols more frequently than would be predicted by random chance; implying that they could, at least partially, grasp the idea that the absence of something is the lowest possible quantity.

It may sound simple to an adult human, but such reasoning represents a huge mental leap because the animal brain arose to process and respond to the environment around it – a world filled with tangible threats and resources that presents no inherent representation for nothingness. 

"This is a tricky neuroscience problem," Dyer said. "It is relatively easy for neurons to respond to stimuli such as light or the presence of an object but how do we, or even an insect, understand what nothing is?" 

In order to confirm the surprising findings, a collaborator from France repeated the study design. Her group achieved the same results.  

Given the huge gaps on the evolutionary tree that lie between the handful of animals that can understand zero, the collective team concluded that the cognitive ability has arisen multiple times, independently, in response to organisms trying to survive complex environments. (After all, being able to think “there is an absence of cave lions around, therefore it’s safe for me to sleep” is quite advantageous.)   

And considering the capacity seemingly requires shockingly few brain cells, they speculate that it is likely to be present in many more species.