06/03/2016

Bumblebees Pick Up On The ‘Buzz’ From Flowers

12:10 minutes

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.”

Bumblebee showing the array of hairs on its body. Image courtesy of Gregory Sutton, Dom Clarke, Erica Morley, and Daniel Robert
Bumblebee showing the array of hairs on its body. Image courtesy of Gregory Sutton, Dom Clarke, Erica Morley, and Daniel Robert

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.”

—Elizabeth Shockman (originally published on PRI.org)

Segment Guests

Erica Morley

Erica Morley is a Senior Research Associate in  Sensory Biophysics at the University of Bristol in Bristol, England.

Gregory Sutton

Gregory Sutton is a Royal Society University Research Fellow at the University of Bristol in Bristol, England.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Bumblebees, you’ve got to admit, are an engineering marvel. The furry flying insects can beat their wings up to 200 beats per second. They can hover in mid-air before landing on a flower, which is no small mechanical feat. And they can pick up UV light that we cannot see.

What’s more, researchers now say that bumblebees can pick up tiny electric signals coming from the flowers, and they do this by using their hairy bodies, through the hair. The results were published this week in the journal, The Proceedings of the National Academy of Sciences. My next two guests are two of the authors on that paper. Erica Morley is the Senior Research Associate at the School of Biological Sciences, University of Bristol in Bristol, England. Welcome to Science Friday.

ERICA MORLEY: Hi.

IRA FLATOW: Hi.

ERICA MORLEY: It’s great to be here.

IRA FLATOW: Thanks for staying up late. Gregory Sutton is Royal Society University research fellow, also with University of Bristol. Welcome, Dr. Sutton.

GREGORY SUTTON: Hello, wonderful to be here.

IRA FLATOW: Dr. Sutton, color falls on the electromagnetic spectrum. Are we talking about color? Is that what the electrical signals are?

GREGORY SUTTON: No, 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. There’s 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 a bumblebee. And that allows a bumblebee to tell how much charge is on a flower’s petals.

IRA FLATOW: Well, let me go through a couple of fascinating things about that, because as interesting as it is that bees can pick up electrical fields, it’s even as fascinating to me that the flowers are putting out an electric field. How do they do that?

GREGORY SUTTON: Well, there’s two ways. The first way is that the flowers have electrical charge distributed on their petals. Not very much. It’s a very small electrical field, which is why we’re quite astounded that bees can actually detect it.

And the other way flowers can generate electric fields is that there is a passive electric field in the atmosphere almost all the time. It’s generated by electrical activity around the world. And on a calm day, the electric field has about a magnitude of about 100 volts per meter. So if a flower just grows up to 30 centimeters above the ground, it will be at the ground potential but the air around it will be at 30 volts of potential, and it will have a very small static electric field just passively.

IRA FLATOW: So the petals don’t get grounded and lose their–

GREGORY SUTTON: No, the petals are grounded, but the air around it is not grounded.

IRA FLATOW: Oh.

GREGORY SUTTON: And that’s the difference that gets you an electric field.

IRA FLATOW: And do different petals have different sized fields?

GREGORY SUTTON: Yes, there’s 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.

IRA FLATOW: And how did you discover that the bees are actually picking up on this electric field?

GREGORY SUTTON: We gave them an experiment where– we gave them an arena that had 10 flowers that we’d built, and all the flowers had the same shape, the same size, the same smell. And half of them had sugar water that the bees could drink from, and the other half had water that was filled with bitter quinine that bees don’t smell, but they don’t like the taste of. And you then put the sugar water flowers– you give them a small static electric field, about 30 volts is what we gave them.

And then you let bees forage through the chamber, and you keep on moving the flowers around so the bees don’t learn the locations of the flowers. And as they forage, they start to go to the flowers with the sugar water 80% of the time. So you know they’ve figured out the difference between the two sets of flowers.

IRA FLATOW: Now Dr–

GREGORY SUTTON: So next up–

IRA FLATOW: I’m sorry. Go ahead. No, finish please.

GREGORY SUTTON: So 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.

IRA FLATOW: Tiny little field they can pick up. That’s fascinating. Dr. Morley, we know that sharks, dolphins, other sea creatures use electric field to detect their surroundings. Is this bee electroreception the same thing? Similar?

ERICA MORLEY: No. So it’s a completely different mechanism. So the aquatic animals all use– well, the signal is conducted through a very conductive medium, so water conducts electricity very well. And so their receptors rely on this conduction, and they’re actually– they use jelly filled sensors that conduct the signal from the water into sensory cells that look at the potential difference between the electric field on the skin and at the receptor, the cell itself.

What we found in bees is that they’re using a mechanoreceptor, so 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.

So air doesn’t conduct electricity very well. It’s very resistive. So these hairs are moved in response to the field, which then causes the nerve impulses from the cells at the bottom of the hair.

IRA FLATOW: Dr. Sutton, how did you know it was the hair that’s doing it and not the antenna or some other part?

GREGORY SUTTON: So we did two sets of experiments. The first set of experiment– the first experiment is we used a device called a laser vibrometer that can measure movements very precisely, and we measured how much movement various parts of the bee was engaging in in response to an electric field. And the antenna moves a little bit, and the feet move a little bit, and various parts– the wings– various parts of the bee move a little bit.

But then we used a device called an extracellular electrode, which is a very, very sharp needle that you can use to record the signal that the part of the body sends back to the nervous system. And when we used an extracellular electrode on the antenna, we didn’t see any signal being sent back to the nervous system in response to an electric field. But when we used the electrode on a hair, we were able to measure the signal the hair sent back to the nervous system.

IRA FLATOW: That’s fascinating. So what does the bees antenna do then?

GREGORY SUTTON: Everything else. Well, it does smell. It does scent. It does warmth. It actually can feel wind. It detects pheromones.

There are so many sensors in the antenna that it’s very astounding, which is why we looked at the antenna first. We just couldn’t find any evidence that there was a electroreception in the antenna.

IRA FLATOW: Looks like– it’s sort of like there’s an app for that in the antenna.

ERICA MORLEY: Well, maybe, but we couldn’t find it.

[LAUGHTER]

IRA FLATOW: Dr. Morley, we have these little hairs inside of the ear that help us detect sound. Are bee hairs acting in the same way?

ERICA MORLEY: So we do have hairs in the ear that are moved backwards and forwards mechanically, much like the bee has. And in fact, a lot of insights will use a structure similar to hairs to hear. So mosquitoes and fruit flies use their antennae to hear from, which are a structure much like the hairs of the bee except they only have two of them. And a lot of other insects use hairs to detect airflow, so they’ll use it to detect the airflow of an approaching predator or their prey, or even mating signals.

IRA FLATOW: Wow. Are there different types of hair that they have?

ERICA MORLEY: Bumblebees?

IRA FLATOW: Yeah.

ERICA MORLEY: It does look like there are several types of hairs. So they’ve got mechanosensory hairs, different kinds of mechanosensory hair, and they’ve also got chemosensory hairs. The antenna’s covered in these little chemosensory hairs, yeah.

IRA FLATOW: You study how insects detect sound. Do these bumblebees hear in the ways that humans think of it? Do they have bee ears like we do?

ERICA MORLEY: I don’t think anyone’s really looked at bees– bumblebees that is. Honeybees are thought to hear using their antennae, but only only older honeybees are thought to do this. So the ones that go foraging, and they’ll use it in their waggle dance. So they’ll go out, forage, find a good source of food, come back, and want to tell the other workers about it. And they make a bit of a buzz, which the other foragers, which are the older bees, will detect using their antennae.

But the social structure in bumblebees is not the same. They’re a much smaller colony, and they don’t do a waggle dance, so this information transfer might not be necessary. So we don’t really know whether bumblebees are using the antenna in this way to detect sound.

IRA FLATOW: Gregory, are the flowers out there competing for the bees attention by the charges that they give off? If you were to go in the field?

GREGORY SUTTON: They’re not competing for the attention, the flowers are identifying themselves–

IRA FLATOW: Ah.

GREGORY SUTTON: –like an advertising brand. When a bee leaves the hive for the first time, it doesn’t have a favorite kind of flower. It is foraging, trying to find any flower.

But let’s say it encounters a buttercup first. It tries to get pollen and nectar from the buttercup, and it takes the bee forever to figure out how to open up the pollen and nectar. After that point, the bee’s figured out how to get pollen and nectar from buttercups, and it will try to stick to buttercups if it can.

And 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.

IRA FLATOW: Does it help it return to that field with the butter–

GREGORY SUTTON: It remembers the location. The bee remembers the location where the flowers are. I don’t think– the electric field is more for identification instead of location.

IRA FLATOW: Mm-hmm. So what’s the next step for you in this study about these bees?

GREGORY SUTTON: So the next step for us is that we– this mechanism that bumblebees have, use of the fuzzy hairs, is a very common mechanism that many insects have. There are a lot of hairy insects. There are flies, and butterflies, and moths, and there are other arthropods, such as spiders and scorpions that also have sensory hairs. And we suspect that detection of electric fields, these small electric fields, might be very common in the arthropod world, and we’d like to figure out whether bumblebees are special, or whether this is all over the place. And we just found it in bumblebees, because that’s where we looked first.

IRA FLATOW: Dr. Morley, do you agree?

ERICA MORLEY: Oh, absolutely. I am very keen to see how far this is spread, and whether we just got lucky with the bees. I doubt it. I suspect this is more widespread than–

IRA FLATOW: Yeah.

ERICA MORLEY: –than just the bees.

IRA FLATOW: Why should this be unique–

ERICA MORLEY: Exactly.

IRA FLATOW: –just to the bees if nature has experimented, and it’s been successful? Might have spread the wealth a little bit.

ERICA MORLEY: Exactly. If that signal there– if the electrostatic signal is all around, then they’re going to have exploited it.

IRA FLATOW: Do we give off one?

GREGORY SUTTON: Yes.

IRA FLATOW: We do?

GREGORY SUTTON: We do. Many, many animals have a small amount of electrical charge, from large ones all the way to small ones. Many, many insects are electrically charged. Bumblebees, honeybees– they’ve been doing measured moths, flies. Birds are electrically charged.

The signal is all over the place. There’s no reason why insects wouldn’t want to take advantage of it.

IRA FLATOW: Well, that explains some attraction. Attractive forces there. I’m just not going to go there.

Erica Morley, a Senior Research Associate at the School of Biological Sciences at the University of Bristol in Bristol, England. Gregory Sutton is a Royal Society University research fellow also at the University of Bristol. Thanks for staying up, and thanks for sharing your knowledge with us and have a great weekend.

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