As bumblebees bumble around your backyard, a hidden force might be helping them find flowers. Beyond sight and smell, these plump pollinators also have an uncanny knack for sensing flower power in the air — and now we finally know how.
Flowers give off weak electric fields, and scientists have known for decades that this helps with pollination, prompting pollen to leap from negatively charged flowers onto the body hair of positively charged bees. In 2013, researchers from the U.K. made another big discovery, revealing that bees can actually sense these electric fields.
But how? That remained a mystery until now, thanks to a new study by the same University of Bristol researchers. They found that a bumblebee's tiny body hairs bend in response to weak electric fields, and that it senses this bending with neurons at the base of its hair sockets. The short video below includes actual footage of this happening, along with an animation explaining how the overall process works:
Any plant connected to the ground generates a weak electric field, and that field is unique to each flower's species, shape and distance from the ground. In the new study, researchers simulated a flower's electric field, then used a laser vibrometer to see if the electricity caused any subtle movements of a bee's antennae or hairs.
"Both hairs and antennae move like a stiff rod," the researchers write, "pivoting the base where mechanosensory neurons are located." Yet when exposed to electric fields, the hairs moved more quickly and with greater displacements than the antennae. And when the researchers looked at electrophysiological responses, they found that only the hairs passed along the signal to a bee's nervous system.
The ability to sense electric fields, known as "electroreception," may come from the stiff, lightweight nature of bee hairs, the researchers suggest, creating a "lever-like motion similar to acoustically sensitive spider hairs and mosquito antennae."
Electroreception is common in many aquatic animals like sharks, which look for prey by detecting electrical fluctuations in seawater. But it's poorly understood in terrestrial animals, and the study's authors say this discovery raises the possibility that it's more common than we thought.
"We were excited to discover that bees' tiny hairs dance in response to electric fields, like when humans hold a balloon to their hair," says lead author Gregory Sutton in a statement. "A lot of insects have similar body hairs, which leads to the possibility that many members the insect world may be equally sensitive to small electric fields."
It's still unclear how important this skill is for bumblebees, which can also find flowers by sight and smell. But it may offer a helpful boost in certain situations, even if bees can only sense electric fields within 10 centimeters. As Viviane Callier points out in Science, that wouldn't be very useful for big animals like humans, but 10 centimeters is several body lengths for a bumblebee, making it a significant distance.
And given the recent decline of bees in some parts of the world — including domesticated honeybees as well as many native bees and other pollinators — research like this is more important than ever. We still don't fully understand what's killing bee populations, or what might save them, so we need to learn as much as we can about their biology while there's still time. Even if we can't sense the electric fields emanating from flowers, we'd certainly feel the shock of a world without bees.