Bumblebees surprise scientists by showing a sense of rhythm

Bumblebees learned to recognize Morse code-like sequences of flashing lights and vibrations, demonstrating a sense of rhythm never before seen in an animal with such a small brain.

The ability to recognize flexible, abstract rhythms—when, for example, the same pattern or melody is played at a different tempo in different ways—has been demonstrated in only a few birds and mammals, including parrots, songbirds, and primates such as chimpanzees.

Andrew Barron at Macquarie University in Sydney, Australia, and his colleagues conducted a series of experiments to try to determine whether bumblebees flu (Bombus terrestris), which have much less complex brains, could also recognize a variety of different rhythms.

In the first experiment, bumblebees were taught to choose between two artificial flowers made up of flashing LED lights. One flower emitted long flashes and the other short pulses, like dashes and dots in Morse code. One flower contained a reward—sucrose—and the other the unpalatable quinine.

Once the bees had learned to distinguish between flashing flowers offering reward and punishment, they were tested with flowers filled only with water. Almost all bees still chose the flower producing the type of flash that previously contained sucrose.

Next, the researchers increased the complexity of the light stimuli, with each flower emitting a different flash pattern—either dash dash dot dot or dot dash dot dash. The bees could still tell them apart.

But then came a truly “remarkable” result, Barron says. The artificial flowers were replaced by a maze and there was a vibrating floor at the intersection of the two branches.

“If it was a dot-dash-dash vibration, that meant turning right to get sugar,” says Barron. “So one rhythm indicated a left turn, one rhythm indicated a right turn, and that’s how we trained them. We showed that they could learn that.”

Finally, without further training the bees, the researchers replaced the vibrating floor with LED lights flashing in the same pattern as the floor. “Not everyone got it, but the population as a whole showed they were able to convert the task from vibrations to light pulses,” says Barron.

In other words, the bees could recognize the pattern regardless of how it was presented. Whether it was flashes of light or vibrating pulses, they recognized the rhythms.

Until now, abstract rhythmic recognition was thought to require the big brain, Barron says. Understanding how bees do this with tiny brains could revolutionize the way miniature drones and other small, autonomous devices interpret the world, he says.

“I think this work shows that there must be an easier trick,” says Barron. “It’s remarkable that an organism like a bee with a bee-type brain is able to abstract rhythm.”

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