Bumblebees surprise scientists by showing a sense of rhythm

Bumblebees learned to recognize sequences of flashing lights and vibrations similar to Morse code, demonstrating a sense of rhythm that has never before been observed 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 pace and in different ways – has only been demonstrated in a few birds and mammals, including parrots, songbirds and primates such as chimpanzees.

Andrew Barron of Macquarie University in Sydney, Australia, and colleagues conducted a series of experiments to try to determine whether buff-tailed bumblebees (Terrestrial Bombus), whose brain is much less complex, could also recognize a whole series of different rhythms.

In the first experiment, the bumblebees learned to choose between two artificial flowers made of flashing LED lights. One flower produced long flashes and the other produced short pulses, like dashes and dots in Morse code. One flower contained a reward – sucrose – and the other contained unpleasant quinine.

Once the bees 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 scientists increased the complexity of the light stimuli, with each flower emitting a different flash pattern – either dash, dot, dot, or dot, dot. The bees could still distinguish them.

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

“If it was a vibrating point, it meant turning right to get sugar,” says Barron. “So one rhythm said turn left, one rhythm indicated turn right, and we trained them like that. We showed they could learn that.”

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

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

Until now, it was thought that abstract rhythm recognition required a 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 a simpler trick,” says Barron. “That an organism like a bee, with a bee-like brain, is able to abstract a rhythm is remarkable.”