Flowers generate weak electric fields, and a new study shows that bumblebees can actually sense those electric fields using the tiny hairs on their fuzzy little bodies.
"The bumblebees can feel that hair bend and use that feeling to tell the difference between flowers," says Gregory Sutton, a Royal Society University Research Fellow at the University of Bristol in the United Kingdom.
People used to think that perceiving natural electric fields was something that animals only did in water. Sharks and eels can do it, for example. The platypus and spiny anteaters were the only land critters known to have electroreceptive organs, but these have to be submerged in water in order to work.
Then, a few years ago, Sutton and his colleagues showed that bumblebees could sense electric fields in the air.
"There is, all the time, a background electric field in the atmosphere," says Sutton. "Any plant that's connected to the ground will generate its own electric field just by interactions with the atmosphere."
He wondered if bumblebees could sense those electric fields and use them in some way. So his team tested that idea with the help of a bunch of almost identical artificial flowers.
The scientists took half of the flowers and put 30 volts on them, then filled them with sugar water. The other flowers were filled with a bitter liquid. "And the bees will eventually learn to go to the ones that are charged to 30 volts," says Sutton.
When they turned off the voltage, the bees lost the ability to differentiate between the flowers and began to forage randomly, showing that the bees really were relying on those electric fields.
But how were the bumblebees able to sense them? That's what the researchers tracked in their latest study, described in the Proceedings of the National Academy of Sciences.
"We used a laser beam that could measure small motions of an antenna or a hair, and that's how we measured how much the air and the antenna moved in response to an electric field," says Sutton.
They also stuck a very fine electrode wire into the nerve at the socket of the bottom of a hair to record the activity of nerve cells there.
"They've got these really fuzzy hairs all over their body, and when they approach something with an electric field, that electric field will bend the hairs on their body," says Sutton. And that bending generates a nerve signal.
The results suggest that bumblebees can sense an electric field produced by a flower that's up to 55 centimeters (nearly 22 inches) away. But that's under ideal conditions in the lab — Sutton says 10 centimeters or so (about 4 inches) is more likely in the real world.
"I'm very excited by this because these little mechanically sensitive hairs are common all over the insect world," says Sutton. "I think this might be something we see in more insects than just bumblebees."
"Basically this just adds to the long list of incredible things that bees can do," says Robert Gegear, who studies pollinating insects at Worcester Polytechnic Institute in Worcester, Mass.
He says it's unclear if bees really use electric fields in the real world, where flowers have a ton of other compelling features, like color and smell.
"And so the one question I have is: 'What is the functional relevance?' — not just from the bee side but from the plant side as well," says Gegear.
For all we know, Gegear says, bumblebees may detect electric fields for something that has nothing to do with flowers, like navigation or communication.
ARI SHAPIRO, HOST:
Bumblebees are covered in hairs, and now scientists have found another reason beyond pollen collection for why they're so fuzzy. NPR's Nell Greenfieldboyce reports on a study that shows bumblebees can use that hair to sense electric fields.
NELL GREENFIELDBOYCE, BYLINE: Scientists used to think that perceiving natural electric fields was something that animals really only did in water. Sharks and eels can do it, for example. But Gregory Sutton wondered about electric fields in the air.
GREGORY SUTTON: There is, all the time, a background electric field. And this is just generated by electrical activity in the atmosphere.
GREENFIELDBOYCE: He says any plant rooted in the ground interacts with the atmosphere and generates its own weak electric field.
SUTTON: A 30-centimeter-high plant will generate about 30 volts' equivalent of an electric field around it.
GREENFIELDBOYCE: It's not something people would notice, but bumblebees do. Sutton is a biologist at the University of Bristol in the United Kingdom. A few years ago, he and some colleagues did some experiments with fake flowers.
SUTTON: All the experimental flowers were the same shape, the same size, the same smell. And then you put sugar water in the ones that you put 30 volts on and normal water in the ones you that you don't put any voltage on.
GREENFIELDBOYCE: The bees quickly learned that the flowers with the electric fields were the sweet ones. Turn those electric fields off and the bees just foraged randomly. Now Sutton has figured out how the bees detect electric fields. His team used a laser beam to measure the small motion of hairs on the bee's body as it got close to one.
SUTTON: When they approach something with a small electric field, that electric field will bend the hairs on their body.
GREENFIELDBOYCE: And that bending generates a nerve signal. The researchers know that because they stuck a very fine electrode wire into the nerve in the socket at the bottom of a hair.
SUTTON: The bumblebees can feel that hair bend and use that feeling to tell the difference between flowers.
GREENFIELDBOYCE: The findings are reported in the proceedings of the National Academy of Sciences.
ROBERT GEGEAR: Basically, this adds to the long list of incredible things that bees can do.
GREENFIELDBOYCE: Robert Gegear studies the behavior of pollinating insects at Worcester Polytechnic Institute. He says it's unclear if bees really use electric fields in the real world to make decisions about what flowers to visit.
GEGEAR: They have a long list of things they can use that are cues that I'd say are probably more reliable and easier to use, like color and odor.
GREENFIELDBOYCE: He says for all we know, bees may use electric fields for something that has nothing to do with flowers, like navigation or communication. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.