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.