Flowers give off electrical signals to bees

Bumblebees use a lot of tools to find nectar in flowers like visual cues and chemical signs. But, as it turns out, they’re also able to detect weak electrical signals that flowers give off.

“We're not talking about color, we're talking about a static electrical field — the same thing as when you charge up a balloon on your head,” explains biomechanics engineer Gregory Sutton. “There is a static electrical charge that pulls on the hair on your head and the static electric charge on a flower’s petals pulls on the hair on the bumblebee, and that allows the bumblebee to tell how much charge is on a flower's petals.”

Sutton and sensory biophysics researcher Erica Morley recently reported their findings about bees’ ability to sense electric signals in Proceedings of the National Academy of Sciences. 

“What we found in bees is that they're using a mechanic receptor,” Morley says. “It's not a direct coupling of this electrical signal to the sensory system. They’re using mechanical movement of hair in a very non-conductive medium. Air doesn't conduct electricity very well — it's very resistive. So these hairs have moved in response to the field, which then causes the nerve impulses from the cells at the bottom of the hair.”

Sutton and Morley made their discovery after putting bees through an experiment. They built 10 flowers with the same shape, size and smell. They put sugar water on some of the flowers and then added small static electric fields to those flowers. On the rest of the flowers, they put bitter water and no electric field. They let the bees loose among the flowers and kept moving the flowers around so the bees couldn’t learn the location of the sugar water. 

“As they forage, they start to go to the flowers with the sugar water 80 percent of the time,” Sutton says. “So you know they've figured out the difference between the two sets of flowers. The last step is you just turn off the voltage and then check to see if they can continue telling the difference. And when we turned off the voltage, they were unable to tell the difference. And that's how we knew it was the voltage itself that they were using to tell the difference between the flowers.”

Sutton says flowers’ electrical charge is distributed on the plant’s petals. 

“It’s a very small electrical field, which is why we're quite astounded that bees can actually detect it,” Sutton says. “[And] there is different charge distribution at different locations on the petals of different species of flowers. So two flowers of the same species will have a similar electric field, whereas two flowers of a different species will have different electric fields.” 

Scientists say bees are capable of remembering locations, so Sutton and Morley think bees use electric fields more for identification purposes than for navigation or locating flowers. 

“They're not competing for attention — the flowers are identifying themselves like an advertising brand,” Sutton says. “The buttercup is telling the bee, ‘I'm a buttercup,’ using its scent, using its shape, using its color. And the electric field is another way that the flower is branding itself so that bees can very easily identify it from far away … The bee remembers the location where the flowers are. The electric field is more for identification instead of location.”

This article is based on an interview that aired on PRI's Science Friday.