Did you know? Bees order numbers from left to right.

Like many humans, bees seem to prefer their number ordered from left to right. Honey bees trained to recognize a specific number tend to fly to the left when given two side-by-side options of a smaller number and to the right when the options represent a larger number, a new study claims. The finding suggests that bees have a mental number line and that this association has biological roots, the researchers report.

Many humans have a mental number line that often places smaller numbers on the left and larger numbers on the right; If you are asked to arrange several bunches of grapes by size, you are likely to line them up by increasing the number of grapes from left to right. Previous work has shown that bees can count and that they even understand the concept of zero, scientists tested 134 bees (Apis mellifera) on their number-sorting abilities using a design developed with researchers who had conducted similar experiments with human chicks and babies.

First, they had to teach their bee students to recognize numbers; Using sugar water, they lured the bees into a test chamber built from a reused wine box. For each bee, they hung a panel on the back of the box with a certain number of symbols (one, three, or five) and fed them sugar water so they would learn to associate the number with food. By varying the appearance of the symbols between visits, they ensured that the bees were learning the number itself and not certain shapes or arrangements.

Then it was time for a test: Researchers removed the training panel and placed two mirror-image panels, one on the left wall of the box and one on the right. These new panels had the same number of symbols as the training panel, fewer symbols, or more. Of the bees trained on one, 72% flew to panel three on the right, but of the bees trained on five, 73% went to panel three on the left, that is exactly the concept of the mental number line.

These results show that mental number lines, or at least some component of them, are present throughout the animal kingdom. This study falls short of explaining why the brains of bees, chicks, and babies have converged in the same numerical order from left to right, but it does offer one possible answer: their asymmetrical brains. All three have brains that process information differently on the left and right sides. A shared system for organizing numbers, if it were really widespread, would highlight how strikingly similar animal minds can be to our own.