Good vibrations

Honeycomb geometry helps dancing bees gather an audience.

If you want to catch someone’s attention on the dance floor, it helps if you’re dancing on a honeycomb. Vibrations from a dancing honeybee are naturally amplified by the hexagonal comb, a new study finds¹.

The work may explain how bees attract observers to the intricate dances that tell them where to find distant food sources. It could also help architects understand how to build earthquake-proof buildings.

The waggling dance of forager bees is „one of the most spectacular forms of animal communication,“ says Thomas Seeley, who studies bees moving and shaking at Cornell University in Ithaca, New York. A single dance can convey the location of a field of flowers as far as 10 kilometres away.

Researchers have long understood how dances encode the location of a food source, but how – in the complete darkness of the hive – the dancer attracts bees to watch the dance has been a mystery.

Clues emerged from previous work by Jurgen Tautz of the University of Wurzburg in Germany, a member of the team that carried out the new study. He showed that dancing bees produce a weak, low-frequency vibration in the comb. When the vibration was blocked, the number of bees that watched a dance dropped by 75 per cent.

But the vibration is produced amid a swarm of tens of thousands of bees. „The riddle for us was how the bees could detect such weak vibrations in such a noisy environment,“ Tautz says.

To figure it out, the team sought inspiration from astronomy. „If astronomers want to detect a very weak signal in space, they don’t use one antenna but several spread out, and compare the results,“ Tautz says. „We thought maybe the bees were doing the same thing, because they have six feet, which can all make contact with different spots on the honeycomb surface to register the vibrations.“

Phased not confused

When the researchers looked at how vibrations spread around the comb, they found that in most places, opposite walls of each hexagonal cell vibrated in the same direction at the same time. But at a distance of two or three cells from the source of the vibrations, the walls vibrated in opposite directions, in what is called a ’phase reversal’.

„We were able to pick up the phase reversal with just two vibration detectors, so it seems likely that the bees can pick it up with their six,“ Tautz says. They found that most of the bees recruited by the dancer came from precisely this phase-shift zone.

„This is a very intriguing finding, because it suggests a source of information that hadn’t been considered before,“ says Fred Dyer, who studies the waggle dance at Michigan State University in East Lansing. But it is possible that other signals alert bees, like airborne vibrations from the dancer’s wings or smells and sounds coming from the dancer, he cautions.

The bees may rely on all these cues together, Seeley says. „Redundancy is a good thing in communication, because it reduces errors.“

Knowledge to build on

It’s not clear why the hexagonal arrangement of honeycomb cells should create this phase reversal, says Tautz. But understanding the phenomenon might be valuable not just for bee experts but for architects. Tautz is working with architects at the California Institute of Technology in Pasadena to design better steel skeletons for high-rise buildings.

„Vibrations in honeybee nests are like miniature earthquakes generated by the bees, so it’s very interesting to see how the structure responds to it,“ Tautz says. Understanding the phase reversal could help architects predict which parts of a building will be especially vulnerable to earthquakes, he says. They could then strengthen these areas, he suggests, or even introduce weak spots into non-critical areas of buildings to absorb harmful vibrations.

References

1. Tautz, J. et al. Phase reversal of vibratory signals in honeycomb may assist dancing honeybees to attract their audience. J. Exp. Biol, 204, 3737 – 3746, (2001).