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Humans' invention of zero was crucial for modern mathematics and science, but we're not the only species to consider "nothing" a number. Parrots and monkeys understand the concept of zero, and now bees have joined the club, too.

Honey bees are known to have some numerical skills such as the capacity to count to four, which may come in handy when keeping track of landmarks in their environment. To see whether these abilities extended to understanding zero, researchers trained 10 bees to identify the smaller of two numbers. Across a series of trials, they showed the insects two different pictures displaying a few black shapes on a white background. If the bees flew to the picture with the smaller number of shapes, they were given delicious sugar water, but if they flew toward the larger number, they were punished with bitter-tasting quinine.

Once the bees had learned to consistently make the correct choice, the researchers gave them a new option: a white background containing no shapes at all. Even though the bees had never seen an empty picture before, 64% of the time they chose this option rather than a picture containing two or three shapes, the authors report today in Science. This suggests that the insects understood that "zero" is less than two or three. And they weren't just going for the empty picture because it was new and interesting: Another group of bees trained to always choose the larger number tended to pick the nonzero image in this test.

In further experiments, the researchers showed that bees' understanding of zero was even more sophisticated: For example, they were able to distinguish between one and zero—a challenge even for some other members of the zero club. Advanced numerical abilities like this could give animals an evolutionary advantage, helping them keep track of predators and food sources. And if an insect can display such a thorough grasp of the number zero, write the researchers, then this ability may be more common in the animal kingdom than we think.

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