The Hidden World of Electrostatic Ecology
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Welcome to the Quanta Science Podcast. Each episode we bring you stories about developments in science and mathematics. I'm Susan Vallett. Invisibly to us, insects and other tiny creatures use static electricity to travel, avoid predators, collect pollen, and more. New experiments explore how evolution may have influenced this phenomenon. That's next. Music

Quantum Magazine is an editorially independent online publication supported by the Simons Foundation to enhance public understanding of science. Imagine that you're a honeybee. In many ways, your world is small.

Your four delicate wings, each less than a centimeter long, transport your half-gram body through looming landscapes full of giant animals and plants. In other ways, your world is expansive, even grand. Your five eyes see colors and patterns that humans can't, and your multi-sensory antennae detect odors from distant flowers.

For years, biologists have wondered whether bees have another grand sense that we lack. The static electricity they accumulate by flying could be potent enough for them to sense and influence surrounding objects through the air. It's similar to the charge generated when you shuffle across carpet in thick socks. Aquatic animals such as eels, sharks, and dolphins are known to sense electricity in water, which is an excellent conductor of charge.

By contrast, air is a poor conductor, but it may relay enough to influence living things and their evolution. In 2013, Daniel Robert, a sensory ecologist at the University of Bristol in England, broke ground in this discipline. His lab discovered that bees can detect and discriminate among electric fields radiating from flowers.

Since then, more experiments have documented that spiders, ticks, and other bugs can perform a similar trick. This animal static impacts ecosystems. Parasites, such as ticks and roundworms, hitch rides on electric fields generated by larger animal hosts. In a behavior known as ballooning, spiders take flight by extending a silk thread to catch charges in the sky, sometimes traveling hundreds of kilometers with the wind.

And in 2024, studies from Robert's lab revealed how static attracts pollen to butterflies and moths, and may help caterpillars to evade predators. This new research goes beyond documenting the ecological effects of static. It also aims to uncover whether and how evolution has fine-tuned this electric sense.

Electrostatics may turn out to be an evolutionary force in small creatures' survival that helps them find food, migrate, and infest other living things. This developing field is known as aerial electroreception.

it opens up a new dimension of the natural world. Anna Dornhaus is a behavioral ecologist at the University of Arizona who wasn't involved with the work. I think it's totally fascinating. I think it's really underappreciated. It hasn't really been studied except by this one group, so we're not giving it justice so far. Partially because it's invisible.

And generally visible traits are just more often studied because they're so prominent to us because they're mostly visual animals. Benito Wainwright is an evolutionary ecologist at the University of St. Andrews. He's studied the sensory systems of butterflies and katydids, which include grasshoppers. People are very quick to jump on trees.

what's adaptive in nature. You know, when you see a trait in nature, it must have evolved adaptively. Now, we know that from all these brilliant experiments in electroreception that, you know, electric fields do have a functional role in the ecology of these animals.

That's not to say that they came on the scene originally through adaptive processes. But now that these forces are present, evolution can act on them. Though we can't sense these electric trails, they may guide us to animal behaviors we never imagined. In 2012, Victor Ortega Jimenez stumbled into electrostatics while playing with his four-year-old daughter.

Ortega Jimenez studies the biomechanics of animal travel at the University of California, Berkeley.

He and his daughter were using a toy wand that gathers static charge to levitate lightweight objects, such as a balloon. And we were playing with that, and then we were bored inside the home, and we get outside, and we started to charge things, playing with that. And my daughter took the wand, plugged it into a spider web, and it reacted very quickly. And so I was thinking, what about the insect? The wand attracted the web.

he immediately began to draw connections to his research about the strange ways insects interact with their environments. All matter - wands, balloons, webs, air - strives for balance between its positive and negative particles, or in scientific terms, protons, electrons, and ions. At an unfathomably small scale, Ortega Jimenez's toy buzzes with an imbalance,

A motor draws negative charges inward, forcing positive charges to the wand's surface. This is static. It's like when you rub a balloon against your head. Friction sheds electrons from your hair to the rubber, loading it up with static charge, so that when you lift the balloon, strands of hair float with it.

Ortega-Gimenez considered that in a similar way, friction from beating insect wings could shed negative charges from body to air, leaving the insects with a positive charge while creating regions of negative static. He realized that if a web carries negative charge and insects a positive one, then a spider web might not just be a passive trap. It could move toward and attract its prey electrostatically.

His lab experiments revealed precisely that. Webs deformed instantly when jolted with static from flies, aphids, honeybees, and even water droplets. Spiders caught charged insects more easily. He saw how static electricity altered the physics of animal interactions.

The magic of animal electrostatics is all about size. Large animals don't meaningfully experience nature's static. We're too big to feel it. Here's Ortega Jimenez again. The reign of electrostatics is important because we are living, us as humans or many animals that are large, they are living mostly in a gravitational or fluid dynamic world. But for tiny beings, gravity is an afterthought.

Insects can feel air's viscosity. While the same laws of physics reign over Earth's smallest and largest species, the balance of forces shifts with size. Intermolecular forces flex beneath the feet of water striders on a pond. Capillary forces shoot water impossibly upward through a plant's thin roots. And electrostatic forces can ensnare any oppositely charged flecks that lie in their path.

Charged fleck is an apt physical description of a pollen grain.

A few years after Ortega Jimenez noticed spider webs nabbing bugs, Daniel Robert's team found that bees can gather negatively charged pollen without brushing up against it. We sort of started through the realization that when an insect, and you can see these things on YouTube videos, when a pollinator or a bee approached a flower, that pollen would jump from the flower to the bee.

And there was no contact basically required between the bee and the flower for that pollen to jump, to transfer between one and the other. And I had a physics student in the lab at the time, and he said, look, this is not a ballistic trajectory. This is a trajectory that responds to electrostatic forces. The discovery suggested to Robert that electrostatics can enable a plant-pollinator mutualism.

That's a well-known example of coevolution. This dynamic was already well established. In it, a bee feeds on a flower's nectar and gathers pollen to feed larvae, and also propagates pollen from flower to flower, enabling plant reproduction. But the potential role of static charge was brand new. Over the past decade, Robert has built a body of work that reveals the many ways insects and arachnids use and experience static.

Ticks jump, spiders balloon, bees sense the negative charge of a flower recently visited by another positively charged bee. He even found that the charged relationship between air and insects goes both ways. Honeybee swarms shed so many negative charges that they alter the electrical gradient around them.

Based on Robert's estimates, the atmospheric charge resulting from a swarm of desert locusts rivals that of clouds and electrical storms. Robert and Ortega Jimenez's conclusions were proactive.

But to them, the physics of arthropods makes electrostatic forces inevitable. "Along the years, you actually measure the charge of all sorts of objects, and you realize that as soon as an object is charged, it will exert force on another object that is charged, and reciprocally, of course, as well.

Because small insects have the tendency to be sharp and angular and have a particular high ratio of surface to volume, all these parameters that the physicists can tell you actually, yeah, that calls for higher charge density.

it turns out that their world is way more electrical than ours. Still, the experiments couldn't conclude that the creatures control this electrostatic function, or how it evolved, if it even did evolve. Robert wondered, is the use of static fields by bugs coincidental or adaptive?

Sam England wears his love of nature on his sleeve. He has a half-dozen animal tattoos, including a treehopper decorated with the planets of our solar system, a nod to his background in physics. The marriage of these worlds drives his curiosity. How does physics mold animal behavior?

He pivoted to sensory ecology for graduate school and joined Robert's lab at the University of Bristol to chase the hypothesis that insects actively use static to affect their environments.

Because the electrostatic world is invisible to human researchers, its forces are hard to study, even before you add unpredictable creatures to the mix. Doing research in biology is so much harder than physics because you have to rely on live animals to do something.

England wanted to test whether Lepidoptera, the order of flying insects that includes butterflies and moths, build up enough static during flight to collect pollen from the flowers they visit for nectar, as bees do. But first, he had to rig up a way to measure the insects' static charge. A walk is England's best analogy for his method of tricking the insects into staying airborne for 30 seconds.

So we built a box. These butterflies would really nicely come to the entrance of the box and then fly through a loop if I mounted the loop near the entrance. But a lot of the other species wouldn't do this. So I had to tie little lassoos around their waists.

And then when you lift up a butterfly or a moth, as soon as their legs aren't touching the ground, they basically start flying because they're like, I'm in the air, so I must need to fly. So I was basically just like flying them around on pieces of fishing line. England says it was like taking a dog for a walk, but with a butterfly or a moth.

Robert explains how it works. We can have them fly through a loop of copper and we can measure an induced charge. And then we can have them approach an object which is mildly conductive, like a flower, and put an electrode in that flower.

And as the insect approaches the flower, let alone land on it, we can see a deflection, either in the potential that is going on, but also in the charge. England studied 11 species of butterflies and moths native to various climates, ecosystems and lifestyles. After they flew around their cages for 30 seconds, enough time to accumulate electrostatic charge, he guided them through the loop. All 11 species charged up during flight.

Some reached static charge of around 5 kilovolts per meter. He calculated that's enough to yank negatively charged pollen from 6 millimeters away.

When winged insects like butterflies and moths land directly on a flower, pollen naturally sticks to their bodies. It's not necessary for them to pollinate because they can always just land on and make contact with the pollen and then it get on them that way. But basically what we're proposing is that because it allows the pollen to be attracted across air gaps, it's going to increase their efficiency as pollinators. So it makes it more likely that pollination will occur.

To gauge static's evolutionary significance, England looked for patterns in how the animal's behavior in the wild correlates with their electrical charge. He found a few. For example, nocturnal moths tend to hold less charge than other species. Why?

England speculates it's possible that strong charges make insects more visible to predators that rely on non-visual cues, such as static, at night. Therefore, minimizing charge could help the moths survive.

Ortega-Gimenez says the paper contains great new data, but he cautions that the study's 11 species are a modest representation of the world's 180,000 or so lepidopterans, which include butterflies and moths. For claiming electrostatic adaptation, I think it needs to be more broad. But it's a good hypothesis. For insects to act on static information, they must be able to detect electrical fields—

Microscopic hairs on bees and spiders seem to aid in sensing, according to work from Robert's lab.

England recently expanded this unresolved science by studying how the minuscule hairs of caterpillars deflect under static to glean how electric information may help a caterpillar survive. We know that these insects are generally building up static charge. Could it be a sensory cue in like the most important ecological interaction, in my opinion, which is predator-prey interactions?

So we measured the charges of wasps and we saw that they are indeed charged. We then used those measured charges to calculate, like we simulated what the electric field could be between like a wasp and a caterpillar sitting on a plant. And then...

That gave us the strength of the electric field that we would expect. And then we exposed caterpillars to these wasps mimicking electric fields, and we saw that they either initiate defensive behaviours or they perform defensive behaviours for a longer period of time. So it basically insinuates that the caterpillars can detect the static electricity and that they also perceive it as an indication that a predator is nearby.

Anna Dornhaus, the behavioral ecologist, questions whether electroreception buys the caterpillar much time. Yet the high stakes of predator-prey conflict suggests that any advantage may count. Predator-prey interactions are a matter of life and death. I mean, for the individual caterpillar, even just getting a small increase in the chance of surviving that encounter, that makes it an evolutionarily relevant behavior.

Ortega-Gimenez is hesitant, but impressed by England's research. And the predators, in terms of organisms, they are always opportunists. Ortega-Gimenez is eager for more data, ideally from wild animals, that examines naturalistic behaviors. So who is winning this game? Who is taking more advantage of the predators?

As more evidence links static to survival, a story is emerging that evolution may fine-tune the capacity to sense or carry charge just like any other trait.

Beth Harris is a graduate student in Robert's lab. The fact that there's such a diverse range of species with different ecologies, I think that's what makes it so interesting because now it's starting to become clear that there's a real treasure chest to be opened. As work continues in Robert's lab, the suspicion that static detection and accumulation among insects and arachnids is no accident does as well.

Caterpillars with better electroreception, or nocturnal moths that carry lower charge, may better dodge predators. If they survive to reproduce more, those genes and traits, including those that help organisms sense and use static fields, could become stronger and more common in generations down the line. It's starting to become impossible to ignore the idea that electrostatics may be more influential in the animal kingdom than we know today.

Whole ecosystems may depend on hidden electric fields. Here's England again. In my opinion, like, it's basically an additional source of information or an additional force to facilitate ecological processes. But it's probably not like, I think the world would keep running without it. If you suddenly took away electrostatics, I don't think you'd get like a mass extinction scenario.

or anything like that. But I think we'd be surprised by how many animals would have to adapt to not using it. Electrostatic forces act on a scale of millimeters and centimeters, but their collective impact could be much larger. For instance, social bees, such as bumblebees, collect food for other colony members and larvae.

Anna Dornhaus studies how bees interact with flowers. Each individual bumblebee has to make these decisions, has to detect a flower, decide whether to land on it, and then extract nectar hundreds and hundreds of times, potentially every day, but certainly thousands of times over their lifetime. And a lot of other individuals essentially depend on that bee being successful in collecting food.

So even if what we think of as maybe on an individual decision level, fairly subtle difference, right? So being able to detect the flower just a second faster or being 10% more accurate in

identifying the correct flower. That seems like a minor effect, but actually, if you think of the bees and how they forage and the fact that they have to make these hundreds and hundreds of decisions in a row and collect enough food for probably 10 of their mates, if you think about it that way, even a fairly small improvement for the bees and detection and

accuracy of decision-making could be quite significant for them evolutionarily. If static charges aid pollination, they could shift plant evolution too. This whole field, you know, studying electrostatic interactions between animals, has the potential to uncover things that didn't even occur to us about how the world works. Maybe some fundamental features of flowers are actually just in the service of generating the correct electrostatic field. And we haven't recognized that because

We can't see them and therefore we've just kind of ignored that whole dimension of a flower's life. The idea isn't so far-fetched. In 2021, Daniel Robert's team observed petunias releasing more compounds that attract bugs around bee-like electric fields. Robert says this suggests that flowers wait until a pollinator is nearby to actively lure them closer.

Dornhaus says we are a visual species, so we might notice different things. Humans are very visually oriented, and so we tend to emphasize flowers that are showy at large and have strong color patterns. But of course, there are many flowers that actually have strong signals in modalities that we can't really perceive as much, either with scent or even in the UV range visually.

And so it may well be that for some flowers, the electric field is actually a more prominent signal to the bees than the color is. Right now, we don't really know that. However, evolutionary details surrounding electrostatic ecology remain murky at best.

Here's evolutionary ecologist Benito Wainwright. It's amazing, really, how little we know. Even within better understood visual and acoustic systems, ecologists are only beginning to connect evolutionary dots.

Because electrostatics has flown under the radar, England worries that humans unknowingly hinder the ability of animals to use these forces by using appliances, electronic devices or even fertilizers. We've discovered this force that's playing a role in a lot of different ecological interactions.

It's also a force that we regularly pollute the environment. We create a lot of electrostatic pollution from power lines or from our electrical appliances in our homes, transformers and all of this stuff. Like we're spitting out electrostatic stuff into the environment all the time. Even our synthetic fibers on our clothing do this. Generally, synthetic materials accumulate more charge than organic ones.

So we're putting in a lot of electrostatic stuff into the atmosphere and into the environment, and we haven't necessarily realized that that could also be interfering with the ecology of lots of animals. England says if insects are sensitive to the wing beat of a wasp, they're probably sensitive to a power line, and it might be messing up that entire system.

Since completing his doctoral work, England now studies animal vision as a postdoctoral researcher with Berlin's Natural History Museum.

He hopes to one day run his own lab to explore these conservation questions and discover new cases of aerial electroreception and electrostatic behaviors, such as mating. The dream would be that electrostatic sensing, or like aerial electroreception, is well known and considered to be a regular part of the sensory repertoire of animals. I think for it to just be seen as one of the senses that's widely known and understood would be amazing.

Realizing that dream will take more research that seeks out the evolutionary secrets of critters far smaller than us and thereby enlarges our world.

Arlene Santana helped with this episode. I'm Susan Vallett. For more on this story, read Max G. Levy's full article, The Hidden World of Electrostatic Ecology, on our website, quantamagazine.org. Explore math mysteries in the quanta book, The Prime Number Conspiracy, published by the MIT Press. Available now at amazon.com, barnesandnoble.com, or your local bookstore.