Honeybees understand that "nothing" can be "something" that has numerical meaning, showing that they have a primitive grasp of the concept of zero.
That's according to a newly published study in Science, which shows that bees possess a mathematical ability once thought to exist only in dolphins, primates, birds and humans who are beyond the preschool years.
"This is quite amazing, in my view, that bees can really do it," says Andreas Nieder, a scientist who studies how animals' process the idea of "nothing" and was not part of the research team.
He says zero was discovered relatively recently in human history, and was essential in the development of both mathematics and science. "It's a hard and very abstract concept," Nieder says. "It is a sort of eccentric uncle in the number family."
Previous experiments have shown that honeybees have some facility with numbers, because they were able to count landmarks as they foraged around for a sweet reward. But in these tests, the insects couldn't count very high — only to about four.
Still, that made a team of researchers in Australia and France want to explore what else the bees could do with numbers. Scarlett Howard at RMIT University in Melbourne, Australia, lured bees to a wall where they were presented with two square cards. Each card had a different number of black symbols, such as dots or triangles.
Howard trained one group of bees to understand that sugar water would always be located under the card with the least number of symbols. "They could come and see two circles versus three circles, or four triangles versus one triangle, or something like that," she explains.
The bees quickly learned to fly to the card with the fewest symbols, an impressive feat.
But then they got another test: The researchers presented the bees with a card that had a single symbol — and a blank card that had nothing on it.
The bees seemed to understand that "zero" was less than one, because they flew toward the blank card more often than you'd expect if they were choosing at random — although they weren't that good at distinguishing between the two.
It got easier for them when they had to compare zero with a larger number. "When we showed them zero versus six, they did that at a much higher level than zero versus one," Howard says. "So what tells us is that they consider zero as an actual quantity along the number line. They're actually better at doing zero versus six because those two numbers are further apart."
Even very young children, she points out, have trouble understanding that zero is a number. "It's easy for them to count 'one, two, three, four,' but zero, it's nothing, it's not something to count. So it's not the same category," she explains.
She had expected that the bees would see a blank paper as something irrelevant that was completely different than what they had been trained on, because to understand zero, "brains need to represent something out of nothing. It's not trivial."
What's more, the brains of bees are incredibly tiny brains compared with the brains of humans, Nieder notes. "Bees really have a mini-brain with fewer than one million brain cells," he says, "compared to 86 billion nerve cells in our brain."
Even so, the bees can understand the abstract concept of an empty set — the precursor or prerequisite to understanding the symbolic number zero — and he says he found that very surprising.