National Geographic

Bees Can Sense the Electric Fields of Flowers

A bumblebee visits a flower, drawn in by the bright colours, the patterns on the petals, and the aromatic promise of sweet nectar. But there’s more to pollination than sight and smell. There is also electricity in the air.

Dominic Clarke and Heather Whitney from the University of Bristol have shown that bumblebees can sense the electric field that surrounds a flower. They can even learn to distinguish between fields produced by different floral shapes, or use them to work out whether a flower has been recently visited by other bees. Flowers aren’t just visual spectacles and smelly beacons. They’re also electric billboards.

“This is a big finding,” says Daniel Robert, who led the study. “Nobody had postulated the idea that bees could be sensitive to the electric field of a flower.”

Scientists have, however, known about the electric side of pollination since the 1960s, although it is rarely discussed. As bees fly through the air, they bump into charged particles from dust to small molecules. The friction of these microscopic collisions strips electrons from the bee’s surface, and they typically end up with a positive charge.

Flowers, on the other hand, tend to have a negative charge, at least on clear days. The flowers themselves are electrically earthed, but the air around them carries a voltage of around 100 volts for every metre above the ground. The positive charge that accumulates around the flower induces a negative charge in its petals.

When the positively charged bee arrives at the negatively charged flower, sparks don’t fly but pollen does. “We found some videos showing that pollen literally jumps from the flower to the bee, as the bee approaches… even before it has landed,” says Robert. The bee may fly over to the flower but at close quarters, the flower also flies over to the bee.

This is old news. As far back as the 1970s, botanists suggested that electric forces enhance the attraction between pollen and pollinators. Some even showed that if you sprinkle pollen over an immobilised bee, some of the falling grains will veer off course and stick to the insect.

But Robert is no botanist. He’s a sensory biologist. He studies how animals perceive the world around them. When he came across the electric world of bees and flowers, the first question that sprang to mind was: “Does the bee know anything about this process?” Amazingly, no one had asked the question, much less answered it. “We read all of the papers,” says Robert. “We even had one translated from Russian, but no one had made that intellectual leap.”

To answer the question, Robert teamed up with Clarke (a physicist) and Whitney (a botanist), and created e-flowers—artificial purple-topped blooms with designer electric fields. When bumblebees could choose between charged flowers that carried a sugary liquid, or charge-less flowers that yielded a bitter one, they soon learned to visit the charged ones with 81 percent accuracy. If none of the flowers were charged, the bees lost the ability to pinpoint the sugary rewards.

But the bees can do more than just tell if an electric field is there or not. They can also discriminate between fields of different shapes, which in turn depend on the shape of a flower’s petals and how easily they conduct electricity. Clarke and Whitney visualised these patterns by spraying flowers with positively charged and brightly coloured particles. You can see the results below. Each flower has been sprayed on its right half, and the rectangular boxes show the colours of the particles.

 

Coloured particles reveal the electric fields of flowers. From Clarke et al, 2013

Coloured particles reveal the electric fields of flowers. From Clarke et al, 2013

The bees can sense these patterns. They can learn to tell the difference between an e-flower with an evenly spread voltage and one with a field like a bullseye with 70 percent accuracy.

Bees can also use this electric information to bolster what their other senses are telling them. The team trained bees to discriminate between two e-flowers that came in very slightly different shades of green. They managed it, but it took them 35 visits to reach an accuracy of 80 percent. If the team added differing electric fields to the flowers, the bees hit the same benchmark within just 24 visits.

How does the bee actually register electric fields? No one knows, but Robert suspects that the fields produce small forces that move some of the bee’s body parts, perhaps the hairs on its body. In the same way that a rubbed balloon makes you hair stand on end, perhaps a charged flower provides a bee with detectable tugs and shoves.

The bees, in turn, change the charge of whatever flower they land upon. Robert’s team showed that the electrical potential in the stem of a petunia goes up by around 25 millivolts when a bee lands upon it. This change starts just before the bee lands, which shows that it’s nothing to do with the insect physically disturbing the flower. And it lasts for just under two minutes, which is longer than the bee typically spends on its visit.

This changing field can tell a bee whether a flower has been recently visited, and might be short of nectar. It’s like a sign that says “Closed for business. Be right back.” It’s also a much more dynamic signal than more familiar ones like colour, patterns or smells. All of these are fairly static. Flowers can change them, but it takes minutes or hours to do so. Electric fields, however, change instantaneously whenever a bees lands. They not only provide useful information, but they do it immediately.

Robert thinks that these signals could either be honest or dishonest, depending on the flower. Those that carpet a field and require multiple visits from pollinators will evolve to be truthful, because they cannot afford to deceive their pollinators.  Bees are good learners and if they repeatedly visit an empty flower, they will quickly avoid an entire patch. Worse still, they’ll communicate with their hive-mates, and the entire colony will seek fresh pastures. “If the flower can signal that it is momentarily empty, then the bee will benefit and the flower will communicate honestly its mitigated attraction,” says Robert.

But some flowers, like tulips or poppies, only need one or two visits to pollinate themselves.  “These could afford to lie,” says Robert. He expects that they will do everything possible to keep their electric charge constant, even if a bee lands upon them. They should always have their signs flipped to “Open”. Robert’s students will be testing this idea in the summer.

Many animals can sense electric fields, including sharks and rays, electric fish, at least one species of dolphin, and the platypus. But this is the first time that anyone has discovered this sense in an insect. And in the humble bumblebee, no less! Bees and flowers have been studied intensely for decades, maybe centuries, and it turns out that they’ve been exchanging secret messages all this time.

Now, Robert’s team is going to take their experiments from the lab into the field, to see just how electrically sensitive wild bees can be, and how their senses change according to the weather. “We are probably only seeing the tip of the electrical iceberg here,” he says.

Reference: Clarke, Whitney, Sutton & Robert. Detection and Learning of Floral Electric Fields by Bumblebees. Science http:/dx.doi.org/10.1126/science.1230883

Thanks to Liz Neeley for a chat about dishonest signalling, which inspired part of this piece.

More on electric senses:

More on bees and pollination from National Geographic:

 

There are 15 Comments. Add Yours.

  1. Patrick
    February 21, 2013

    Haven’t read the study but as described its very weak. Sweet & charged vs bitter & uncharged says nothing about electrical attraction. Try ch vs unch, both sweet and both bitter. Bumblebees communicate/discriminate sweetness of nectar. Static chrg of bee bodies has been observed for centuries. Speculation about flowers here is anthropomorphic.

  2. Toos
    February 21, 2013

    Nice story and nice picture again! Thank you!
    Though I missed these: “Clarke and Whitney visualised these patterns by spraying flowers with positively charged and brightly coloured particles. You can see the results below.” Where there are no pictures, my screen shows just 3 white lines. Is something wrong with my browser or with the uploades or whatever? And – most important – is this fixable somehow?

  3. Toos
    February 21, 2013

    Ha, there it is, the flowers-picture :) ! Thanks, for the quick repair too!

  4. Damara Arrowood
    February 22, 2013

    It would be nice to see a graphic or diagram of an electrical field around a flower. Do any images exist that aren’t “Kirlian” photography?

  5. Patrick Clarkin
    February 22, 2013

    I’m not an entomologist, so almost everything coming from that field is new to me. But it is still pretty humbling to realize how many mysteries are still out there in nature. Thanks for bringing these studies to our attention, Ed.

  6. Bob Hastings
    February 22, 2013

    Might this be a base for designing a device to help the blind to see?

  7. Kristen
    February 22, 2013

    In response to Patrick – It is a good study design for what it is, which is determining the sensory ability of the bees, not whether they use it in the wild (which is the next step). It is similar to training a mouse to press a green button for a cheese reward, not the red. If the mouse is color-blind, he’ll only get it right half the time (assuming all other factors are controlled for), bur if he can tell the difference, he’ll quickly learn which one to push. Here, the bees were able to sense which of the identical flowers to visit because they could sense its charge and had learned to associate the charge with the reward.

  8. Fiona
    February 22, 2013

    sure makes you wonder about EMF radiation, cell towers, routers, smart meters

  9. Gracie
    February 22, 2013

    Perhaps they can look further into this and see if this has anything to do with the decline of bees. Perhaps engineered cell phones are trashing bees abilities to sense the natural charges and can’t find the pollination needed to survive.

  10. Hilary Cox
    February 22, 2013

    Bumblebees are anything but ‘humble’! They are doing a job we as a race need to recognise for its importance. Without their services, and the many other pollinators’, the human race is a gonner!

  11. kevin_hingwanyu
    February 22, 2013

    Flying bumblebees carry positive electrical charge. I guess, when two bees fly too closely their electrostatic fields would repel each other. Television says that the structure of bee is not engineered for aerodynamic (don’t ask me to explain what’s aerodynamically impossible). Heresay bees can fly which is not possible and a mystery. Besides this, flying bumblebees carrying electrical charge may be another reason why their flying are hard to manage. Flowers attract bees literally. Is the electric attraction also helpful for bees to search remote flowers?

    At this moment I don’t know how to properly say this – I think I have found a very important answer in nature, bees carry positively electrical charge while flowers are slightly negative so the pollen are electrostatically negative too. Bees and pollen carrying opposite electrical charges this will enhance the effect for bees to collect and attract pollen. And it also tells why much smaller pollen are favored for better pollenation.

  12. Kudzu
    February 24, 2013

    In response to Kevin; bumblebees cannot fly if you treat them like tiny airplanes with fixed wings, which they are not. The ‘impossibility’ tells us we are using the wrong equations and when you treat them like the little buzzers they are with flapping wings you see that yes, they can indeed fly.

  13. kevin_hingwanyu
    February 24, 2013

    [
    In response to Kevin; bumblebees cannot fly if you treat them like tiny airplanes with fixed wings, which they are not. The ‘impossibility’ tells us we are using the wrong equations and when you treat them like the little buzzers they are with flapping wings you see that yes, they can indeed fly.
    ]

    I think the television had considered the shape/geometry of the wings of bees which are different from airplanes’ fixed wings, when the television program claimed that bees are aerodynamically not workable. From layperson’s view, I think, intuitively, bees and mosquitoes are flapping their wings at very high frequency where we can hear the high frequency sound when they are flying nearby or hummingbirds flying in television. Flapping wings with relatively high frequency this could solve most query about their flight, and, their relatively heavier body, non-streamlined shape not are main problems. This suggests that their ability of flight is not too odd at all. In reality, bees, mosquitoes and hummingbirds can do hovering or suspending in air in addition of flying. I recall that an article in phyx_org says that wings or tails of other shape/geometry when flapping in fluids it would generate turbulence at behind or below. Those turbulence would provide lifting or propelling.

    To equate wings of bees or mosquitoes to aeroplanes’ fixed wings is off the focus. I think, intuitively, to equate/relate/associate wings of bees to a propeller or the rotating part of turbine of airplane is much closer to the solution of the speculation, although it is still perhaps not the solution exactly. In addition of flapping wings at high frequency, I think it is also important that their wings can twist or change angle when they are flying, or the conformation or shape (of their wings) are changing when they are flying.

    So you think there are already some equations can succeed to describe their flying mathematically, they can fly which is no longer a mystery ? I think they can fly, is a reality, just the programmes on television do not find those equations yet.

  14. Janice
    February 28, 2013

    Hi Daniel, I would like to suggest studying the difference in electrical charges of insects and spider webs. I know spiders have deposits on certain strands of their web so that through a fly’s eye, their web looks like the shape of a flower, with the spider sitting in the centre, but it would interesting to know if there is also electrical fields involved.
    Janice McGuigan

  15. john goff
    November 6, 2013

    Does anyone know of a recent study on the effects of running 400kv power lines, for example, through a valley populated with numerous honey bee farmers?

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