Bumblebees surprise scientists by showing a sense of rhythm

Bumblebees have learned to recognise Morse code-like sequences of flashing lights and vibrations, demonstrating a sense of rhythm that has never been seen in such a small-brained animal.

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

Andrew Barron at Macquarie University in Sydney, Australia, and his colleagues ran a series of experiments to try to determine whether buff-tailed bumblebees (Bombus terrestris), which have far less complex brains, could also recognise a range of different rhythms.

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

Once the bees had learned to distinguish between the flashing flowers offering reward and punishment, they were tested with flowers filled only with water. Almost all the 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 emanating a different flash pattern – either dash dash dot dot or dot dash dot dash. The bees could still distinguish between them.

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

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

Finally, with no more training of the bees, the scientists replaced the vibrating floor with LED lights flashing in the same pattern as this floor. “Not all of them got it, but the population overall showed that they were able to transfer the task from vibration into light pulses,” says Barron.

In other words, the bees could recognise a pattern independently of how it was presented. Whether it was light flashes or vibration pulses, they recognised the rhythms.

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

“I think what this work is showing is there’s got to be a simpler trick,” says Barron. “That an organism like a bee, with a bee-type brain, is able to abstract a rhythm is remarkable.”