The Millions Of Ways Animals Sense The World
A shark tracks its victims by smell, but uses the unmissable signal of a fish’s electrical field to make its final strike. Fire-chaser beetles can detect the heat of distant forest fires with specialized cells in their heads. Baby tree frogs can detect the seismic signals of a striking snake from within the egg—and seem to hatch earlier in defense. And the prey-hunting visual system of one unassuming-looking Mediterranean fly, known as the killer fly, works faster than any other species we’ve observed.
All of these are examples of an animal’s umwelt, their specialized sensory bubble or window onto the world, as described by German biologist Jakob Johann von Uexküll over one hundred years ago.
As science writer Ed Yong writes in his newest book, An Immense World: How Animal Senses Reveal The Hidden Realms Around Us, our history of studying animals’ umwelten has been fraught with hubris, misunderstandings, and mistakes. But bit by bit, we’re learning to appreciate the truly spectacular perceptive abilities of the owl, the elephantfish, and the humble jumping spider.
Yong joins guest host Maddie Sofia to share stories of amazing animal sensory abilities and the challenges of both imagining and describing these other realms using human-centric language. Plus, the uniquely human capacity to imagine other animals’ umwelten, and how we can use it to make the world better for them.
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Ed Yong is a science writer and author of An Immense World: How Animal Senses Reveal The Hidden Realms Around Us. (Random House, 2022)
MADDIE SOFIA: This is Science Friday. I’m Maddie Sofia. Pop culture often imagines humans seamlessly entering the worlds of other animals. I mean, the Anamorphs books were big in my house. Or what about this classic? Spidey sense.
SPIDERMAN: Uh oh. My spider sense is tingling. I’m being watched. My spider sense tells me– Uh oh.
MADDIE SOFIA: But the worlds animals experience are vastly different from ours. We’ve never experienced the world through magnetic fields, flowing ocean currents, or high pitched vibrations.
How do you understand a fish that learns by sensing electric fields? Beetles that know no language except the heat of a distant forest fire. Mole rats that make their way around using touch sensitive teeth.
Science writer, Ed Yong, tries to translate for us. He’s interviewed manatees, treehoppers, and 100 different scientists to write his latest book, An Immense World– How Animal Senses Reveal the Hidden Realms Around Us. He’s here today to talk about what he’s learned about the worlds animals perceive that we can only try to imagine. Welcome back to Science Friday, Ed.
ED YONG: Hi. Thanks for having me.
MADDIE SOFIA: Absolutely. OK. So like I mentioned, there are plus different animals mentioned in this book. I saw you got punched by a mantis shrimp.
ED YONG: I did.
MADDIE SOFIA: Shocked by an electric eel. Spent time in deep freeze with hibernating ground squirrels. Tell me what your favorite animal interaction you had was during your research.
ED YONG: Oh, so I went to this lab in Missouri to meet a guy called Rex Cocroft who studies leafhoppers. And these are small insects that live on plants that I think most people have never heard of. But I guarantee you that if you’ve been to any park or green space, you will have been next to a leafhopper at some point.
They send vibrational messages through plants. They vibrate their abdomens and send these seismic signals through the stems and leaves of the plants on which they stand that other leafhoppers can then pick up. These vibrations are inaudible to us.
But if you clip a little microphone onto the plant, you can translate them into sound. And I went to this lab to listen to these vibrational calls myself. And they are astonishing. I saw this tiny little insects sitting on a leaf producing a sound that sounded almost like a lion’s roar, a very deep purring noise that you would never have thought would come from an insect.
And then we went on this prospecting expedition, going to a local park and clipping microphones onto like bits of plants– like little grass stems and so on– trying to find one of these things in the wild. And we eventually found– we heard this noise. It sounded like– I don’t know– it sounded like a fairy hyena laughing.
MADDIE SOFIA: Do you feel comfortable giving me a treehopper impression right now?
ED YONG: I do, because the treehopper is not going to be listening to this.
MADDIE SOFIA: Right.
ED YONG: I’m not going to get canceled for doing a bad treehopper impression.
MADDIE SOFIA: Go ahead, go ahead.
ED YONG: It sounded like [IMITATES TREEHOPPER]. It sounded like a weird snickering noise. And once I convinced myself that it wasn’t, in fact, the scientist just like standing behind me and teasing me, it just felt magical.
Like most of these insects are very rarely studied. Very few people go around clipping microphones onto bits of grass. But when you– so it means that when you do, you stand a reasonable chance of hearing something that no one has ever heard before.
MADDIE SOFIA: Yeah. Oh my gosh, I love that. OK.
I’m also just thinking about all these different sensory systems in your book of all of these animals– manatees, jumping spiders, your corgi, Typo. Was there a sensory system or like a perspective that you were like, oh I want that. That would be incredible.
ED YONG: Yes. I think there are quite a few. And they’re all my babies, so it’s a little hard to pick between them. I think that in terms of the more exotic senses that we really don’t have access to, dolphin sonar would be truly incredible.
So dolphins have the ability to echolocate. So they [INAUDIBLE] high-pitched calls and they sense the world by bypassing the rebounding echoes. But because of the way sound moves through water, dolphin sonar also penetrates through flesh. An adult dolphin echolocation on you can probably perceive your skeleton, your lungs.
MADDIE SOFIA: I don’t know how I feel about that.
ED YONG: Right. Suddenly– I don’t know, have you ever swum with a dolphin?
MADDIE SOFIA: Yes, I have.
ED YONG: It probably knows stuff about you that even your close friends don’t know, probably.
MADDIE SOFIA: Right.
ED YONG: So I think that experience of essentially being a swimming, living, medical scanner would be the absolutely incredible.
MADDIE SOFIA: I love that.
ED YONG: And then there are also– even for more familiar senses– birds have access to this entire dimension of colors that we can’t see. And if we could, flowers, the feathers of other birds, much of the world would look very, very different.
MADDIE SOFIA: Right.
ED YONG: And I think just being able to briefly get that sense of like a more kaleidoscopic reality would be incredible.
MADDIE SOFIA: Absolutely. OK. So one of the things that you emphasize is the importance of studying animals in their own right. Not just how we can use them or mimic them. Why is that so important, Ed?
ED YONG: I think for a few reasons. I think sometimes our relationships with animals do become a little bit transactional. Scientists study them as model organisms, as windows into our biology. Or they might study them as sources of inspiration, things that could point us to words better technology.
But I don’t really care about any of that. An Immense World is about animals– is about trying to understand animals for their own sake. And I think that’s important, just because they are kind of miraculous. And because their ways of sensing the world are so different from ours.
Our senses give us a perception of the world that feels complete. And that sense of completion is an illusion, we actually are only perceiving a very thin sliver of all there is to perceive. Our world is just a small fraction of the immense world surrounds us. And we can’t access that, unless we really think about what other animals are doing.
So if we ignore them or if we allow them to go extinct, we lose a way of understanding the world around us. And I think our reality becomes a little bit narrower and a little bit more constrained as a result. So it’s really a sort of philosophical argument. I think that if we really want to know what is happening around us, we have no choice but to try and consider the perspectives of other creatures.
MADDIE SOFIA: All right, Ed. So let’s try to consider some of those perspectives of other creatures. And I want to start by talking about that sensory bubble that you alluded to, that all animals live in. The parts of the world that an animal can actually sense. It’s called the umwelt. Where did this word come from?
ED YONG: It was popularized by a German biologist named Jakob von Ueskull. And I’m very sorry to all German speakers for absolutely butchering that. It’s hard, all right.
And so he used the word umwelt comes from the German for environment. But von Ueskull wasn’t using it to talk about the physical environment, not like the plants or the mountains or what have you. He meant the sensory environment, the part of that world that the animal can perceive through its own unique set of eyes, ears, noses, or other sense organs.
The umwelt is the slice of reality that each creature has access to. And it differs radically from one species to another.
MADDIE SOFIA: Yeah. How would you describe the umwelt of your smell-focused pet dog, Typo, for example. Take us into Typo’s brain.
ED YONG: So Typo can see further to the sides than I can, as a simple example. His color vision is more limited than mine. So while my visual spectrum runs from red to violet, his goes from yellow to blue.
But through his nose, the world is far richer than I could possibly imagine. And that’s evident whenever we go for a walk. He sniffs furiously as we trundle along the same streets that I walk along, day in and day out.
And every time we do that, it’s a new adventure to him. He sniffs the plants that he encounters. He sniffs patches of dried pee from dogs that have walked those streets before.
And when he does that, he gets biographical information about those dogs. He knows who’s been there. He knows what they’ve been up to. Maybe he has an idea about their health or what they’ve recently been eating.
To me, Typo sniffing like dog pee on our walk is a little bit like me checking my social media feed. it’s a way for him to connect socially with the other dogs in his world, even when they’re not immediately next to him.
And the parallels between that and me scrolling through Instagram and seeing what my far friends are doing are actually pretty exact. I think that those two things are incredibly comparable.
MADDIE SOFIA: I want to talk about actually studying this stuff, because I can imagine it’s really challenging to study these sensory systems so different from ours. Especially when even our terminology, like ultrasonic, is defined by human sensory ranges and limitations. So talk to me a little bit about that.
ED YONG: Yeah. It’s really hard to escape our own biases. And you touched on a great example. Ultrasonic is almost like anthropomorphic by definition.
That just refers to frequencies over 20,000 Hertz, which is the top of the human hearing range. Actually, most animals– most other mammals certainly– can hear just fine into that range. For them, it’s not ultrasound it’s just sound.
MADDIE SOFIA: Yeah, right.
ED YONG: Right. And similarly ultraviolet, a color that we can’t see but that exists is just beyond the violet end of the rainbow. It’s not really ultra to most of the sighted animal kingdom, which actually can see ultraviolet.
The limitations of our senses then create limitations in our science. So for a long time, scientists kept thinking that seeing ultraviolet was special. That it was the province of just a very narrow range of the animal kingdom. And that it might be used for sending secret messages that most other creatures could not see.
So you might have ultraviolet markings on your face that were only perceptible to your species. But it turns out that if most other animals actually can see ultraviolet, it’s not very secret at all.
MADDIE SOFIA: Absolutely.
ED YONG: It just happens to be another color.
MADDIE SOFIA: Quick reminder that I’m Mattie Sofia and this is Science Friday, from WNYC Studios. Talking to science writer Ed Yong, who has a new book about the amazing sensory worlds of animals. So how do we actually study this stuff. Like give me an example of studying a sense that we don’t remotely have. How we’ve managed to try.
ED YONG: So echolocation is actually a great example of this. And it turns out to be a sense that, despite feeling exotic to most people, is one that is remarkably easy to study. Because to echo-locate, a bat– for example– must produce sound.
So it’s listening for the echoes of its own calls. And without the call, there is no echo. So the bat, to sense the world around it, needs to be making noise. And by changing the nature of those calls, their frequency, their duration, the bat can wrest different information from the world around it.
So a scientist can look at where the bat is aiming its sonar pulses. They can look at the frequency of those pulses. And they can get a sense of what the bat is trying to detect.
Whether it’s trying to search for an insect in open air. Whether it’s trying to navigate around obstacle. Whether it’s homing in for the kill.
MADDIE SOFIA: Yeah.
ED YONG: And that’s sort of incredible.
MADDIE SOFIA: Right.
ED YONG: It means that by recording a bat’s calls, you can almost get at the bat’s intent. And that makes things like echolocation reasonably easy to study. But it also– there’s always going to be a gap.
You’re never going to fully appreciate what exactly is going on in the bat’s head, even though it’s calls give you a sense of what the bat is trying to do with its echolocation.
MADDIE SOFIA: Right. Can I ask you, in a similar vein as how it’s kind of difficult to study these sensory systems. Was it difficult to write about this research? Would you write a sentence and be like, oh, what a human way to write that sentence. You know what I mean?
ED YONG: Right. Yes, very much so. It certainly, in that way, it’s quite hard to avoid anthropomorphisize– isn’t that the right word?
MADDIE SOFIA: That’s right.
ED YONG: It’s quite hard to avoid viewing these creatures through human terms. And I’ve just done it there, right. I’ve used the word “view”, which is a visual term. We are a species whose sighted members rely on vision very heavily.
And our terminology for perceiving the world is heavily influenced by vision. Just that word there, using “view” to mean “perceive” is symptomatic of that. So in writing the book, I tried really hard to not use visual language when I’m talking about non-visual senses.
To not foist human terms on these creatures. And it’s difficult. Because sometimes, there just isn’t an obvious alternative. Especially when you think about sensors like, say, electroreception, so sensing electric fields.
There, the lingo is all stuff like potential, and voltage, and current. Stuff that feels, I think, abstract to most people. It doesn’t come– electroreception doesn’t come with the rich lexicon that sight or sound might have.
MADDIE SOFIA: We have to take a short break. When we come back, more from science writer Ed Yong, author of the new book An Immense World– How Animal Senses Reveal the Hidden Realms Around Us. All about the smell, vision touch, and unique senses animals use to perceive the world.
I’m Maddie Sofia, this is Science Friday. We’ve been talking with science writer Ed Yong this hour about how animals, and I mean non-human animals, sense the world around them. From seeing colors we can’t even imagine, to the faint electrical fields generated by all living things.
He’s written all about it in his new book, An Immense World– How Animal Senses Reveal the Hidden Realms Around Us. There’s an excerpt on our website if you want to take a look, sciencefriday.com/senses. That’s sciencefriday.com/sense.
So let’s dig into some of these sensory systems. And I want to start with I think my favorite that was in the book. You write that animals have been sensing seismic vibrations since they crawled out of the ocean. How is this different than sound, which is like vibrations of the air?
ED YONG: Right. So what we usually think of as sound are waves of pressure moving through the air. But similar vibrations can also course through the ground. Most of these examples are when an earthquake happens, you feel that rippling of the ground.
But that also happens to a much, much smaller extent through more regular activities. Like whenever we walk we send seismic vibrations along the ground beneath us. And if you have the right sense organs, you can detect those vibrations.
And many animals absolutely do that. This world of seismic sensing is often neglected. We tend to focus on the airborne stuff and we neglect all the stuff that goes on beneath our feet.
Like the leafhoppers I talked about at the start of this interview are a prime example of that seismic sense. But there are lots of other creatures– from earthworms to elephants– that also detect these surface-borne vibrations.
And spiders are absolute masters of this. The spiders that build their own webs are effectively extending their sensory systems into the world around them through the architecture that they make with their own bodies.
MADDIE SOFIA: Yeah, absolutely. In one example of seismic sensing that completely blew me away. I was like– I had to put the book down for a second. Baby tree frogs can sense the vibrations of predators while they are inside the egg. I– can we talk about it?
ED YONG: Yes, we can. So this all comes from a long body of work by Karen Warkentin, who is an amazing biologist. So they worked out that at a time when everyone thought that embryos were just passive entities, Warkentin showed that in fact, they are still actually actively sensing the world around them and can sometimes react to that world.
So these baby tree frogs inside their eggs can detect the vibrations of a snake that’s trying to chew on this cluster of eggs. And they will react by releasing an enzyme from their face that dissolves the eggs and allows them to break free and plop into water.
MADDIE SOFIA: I just–
ED YONG: That’s right. That is incredible.
MADDIE SOFIA: Evolution, you know what I mean?
ED YONG: I know, absolutely. This is– good job evolution.
MADDIE SOFIA: Yeah, smart.
ED YONG: It’s solid, solid work, yeah. So these are creatures that are maybe four days old. They might technically– they’re sort of 0 days old, right. They haven’t even hatched yet.
They’re still inside the egg. But they still have an umwelt. They still have an awareness of their surroundings.
And they can differentiate between the kinds of vibrations created by a chewing snake and those created by say, the patter of rainfall or the shaking of the ground. It’s not just that any kind of vibration sends them busting out of the egg. It’s very specifically the vibrations created by predators.
MADDIE SOFIA: Yeah. OK, OK. And then this chapter also– can tell how jazzed I am about this chapter– and then, and then. This chapter also had a really good example of how predators have evolved to exploit the senses of their prey. Kind of the reverse, including their seismic senses. And you have kind of a funny story about some Florida residents who have been unknowingly mimicking the way moles hunt earthworms?
ED YONG: Right. Yes, that’s right. So there is this practice called “worm grunting”, where you create seismic vibrations in the ground by rubbing like iron against a stake. This happens in Florida.
People go out into the woods and they create strong vibrations in the ground. And earthworms start rising up from the ground and then can be collected and used as bait. And it turns out that these vibrations mimic the stimuli created by burrowing moles.
And so the earthworms essentially are trying to flee from what they think is a mole-quake.
MADDIE SOFIA: Right.
ED YONG: But that is, in fact, the work of Floridians inadvertently mimicking a mole.
MADDIE SOFIA: Oh my gosh. OK. So let’s move on to a different chapter, which is a chapter that you wrote about pain. Which I thought was really unique and I hadn’t thought that much about.
You call it the unwanted sense. Give us some pain 101. It turns out there’s a difference between the sensory perception of hurt and the emotional thing we call pain.
I think everybody who’s ever broken a bone or had a chronic illness kind of knows what I mean. We all know the sensation is telling us information. But it’s also different from the great deal of suffering around that information.
ED YONG: Right, totally. So if I touched a hot pan, for example. My arm is going to start recoiling before I realize that I have touched something hot. And that reflex is fueled by what’s called nociception.
There are receptors in my hand that detect that something harmful has– that I touch something harmful. And that forces me to recoil. Then afterwards, shortly afterwards, I feel the pain of the injury.
You know it sucks. I am suffering. That negative emotion is pain.
And there is a distinction between those two, the actual detection of the harm and then the emotional response to it. Now there has been a lot of debate about whether animals have the latter. Like all animals seem to have the former, right. They all do nociception.
They can all recoil from something that’s going to hurt them. But whether they have that emotional suffering or not is something that is very hotly debated. But I think in the middle is where a lot of the reality lies. I think a lot of animals do have an experience of pain.
MADDIE SOFIA: Yeah.
ED YONG: From fish to crustaceans. But I don’t think that it’s going to be exactly the same as what we experience.
MADDIE SOFIA: Right.
ED YONG: I think there’s going to be a lot of variety there. And that’s a little weird, right. I think we think of pain as universal.
But it isn’t. If I get chili oil all over my hand, that’s really going to sting.
MADDIE SOFIA: Right.
ED YONG: The same chemical that causes that sting doesn’t cause pain at all in birds, for example.
MADDIE SOFIA: Right.
ED YONG: Or like naked mole rats. And even closely related animals can experience pain in very different ways. If an octopus injures a tip of its arm, it’ll know oh, arm number 6 is injured. I’m going to look after that.
If a squid has an injury on part of its body, it doesn’t seem to understand which part of its body has been injured. It just seems to have this whole body hypersensitivity.
MADDIE SOFIA: Right.
ED YONG: So even there what we– this idea of pain is going to manifest in very different ways–
MADDIE SOFIA: Yeah.
ED YONG: In animals that we think of as being closely related.
MADDIE SOFIA: OK. This is good, because I want to ask you about something you wrote in your chapter about pain as this unwanted sense. You write that this quest to understand animal pain is a another conversation driven by our own biases.
We’re often asking questions like can I eat this animal, morally. What can I do to this animal. What should we be asking instead?
ED YONG: The more interesting questions, rather than just do animals feel pain or not or, are what kinds of pain do they feel. Like how does that manifest to them. Under what conditions have different types of pain evolved.
You’re right that this is such a charged topic. And it I think makes us forget the nuances that we understand in some different senses. So some people have argued that this distinction between nociception and pain is actually quite artificial.
And it’s not that we make that distinction for things like vision, for example. People aren’t talking about the distinction between photoreception, the detection of light, and vision, the subjective experience of the visual world. Except that distinction absolutely exists. We can very much talk about it. And people do.
It just doesn’t have that same moral charge that talk of pain does. And I think that moral charge is absolutely vital. it shapes the ways we think about caring for animals, like our responsibilities to them. But it shouldn’t stop us from asking these more interesting nuanced questions about exactly what their experience really is like.
MADDIE SOFIA: All right. OK. So we don’t have time to talk about all the chapters and the animals in your book, unfortunately. But we have to talk about the beetles.
ED YONG: I love the beetles.
MADDIE SOFIA: Yeah. OK, more specifically, the beetles that chase forest fires.
ED YONG: Right. So there are a few species of beetles that fly towards forest fires. Which seems to be like the wrong direction, right. Like usually you fly away.
But they fly towards the fires because a charred forest actually is a pretty sweet place to lay your eggs, if you’re a beetle. Your grubs will hatch in an environment where there are no predators, where the trees have been weakened and make for easier meals.
And so these beetles fly towards fires. And have probably the most dramatic sex in the animal kingdom, where they mate amid the flames in this slide amazingly metal way.
MADDIE SOFIA: Yes.
ED YONG: But this ability is contingent on their ability to detect forest fires. And they do that by sensing the heat from those fires, the infrared radiation that those fires give off, over truly incredible distances.
People have documented these beetles arriving at like barbecues, or like a sports stadium at the time when people were smoking cigarettes a lot and you had these thousands of points of heat for these beetles to be distracted by. And, yeah, it’s an absolutely incredible ability.
MADDIE SOFIA: Just a quick reminder that I’m Maddie Sofia and this is Science Friday from WNYC Studios. Talking to Science writer, Ed Yong, who has a new book about who has a new book about the things animals feel that we can’t.
OK. So your book starts with the senses of other animals, but ultimately ends with humans, with us. And what you say is that we, unlike the octopus or the owl, can glory in worlds we cannot perceive with our own senses. That ability is actually our greatest sensory skill. Tell me more about that.
ED YONG: Yeah. If I was in a room with a rattlesnake, a dog, an elephant, an owl, firstly you might question my life choices. But also, you might realize that all of us are going to be experiencing that room in a very, very different way even though we share the same physical space.
But the one thing that I, the human, has that I think is unique is the ability to ponder about what those other creatures are experiencing, the knowledge that their sensory worlds are different to ours. Now there’s a long history of people claiming, wrongly, that humans have some skill that no other animals have. But I think this is a reasonable claim to make in this instance.
Because thinking about other sensory worlds doesn’t come naturally even to humans. It took a lot of philosophy and research to actually get to the point where I can write a book like this. So we have, now, this ability to ask.
Like what does an electric fish sense. What does a bat sense. What does a rattlesnake sense. And that ability to go on these sensory voyages– to try and jump into the umwelt of another creature–
MADDIE SOFIA: Right.
ED YONG: –is a profoundly human gift, and I think that one that we really ought to cherish and not throw away.
MADDIE SOFIA: Yeah, absolutely. Just as a final note, how do we use that gift responsibly? How do we use that gift– that power– for good?
ED YONG: Yeah. At the end of the book I write about the problem of sensory pollution. The fact that we have flooded the world with light and sound in a way that distracts and waylays and harms the other creatures around us. And paradoxically, we– despite the fact that this kind of pollution is very obvious to us– we neglect it.
Because we don’t think of light and sound as possible pollutants. We think of them as good things, part of our lives. But by forcing other creatures to exist in our umwelt we neglect the ways in which they live their lives. And sometimes we end those lives as a result.
I think that thinking about other umwelts allows us to be better custodians of the world, better carers for the other creatures around us. I think it also makes us more profoundly connected to that world. We understand the creatures in it better.
If we remove unwanted sources of light and sound, we can see those creatures better. It’s not for nothing that early on in the pandemic people really realized that they could suddenly hear lots of birds around them that they couldn’t hear before. Because the world was a quieter place.
I think by respecting other umwelts, we become better connected to nature. We recognize that nature is something that exists in our backyards rather than something distant. And I would hope then that we feel a more profound call to care for it and to appreciate it.
MADDIE SOFIA: All right. That’s all the time we have. Ed Yong, thank you so much for joining me today.
ED YONG: Thank you for having me.
MADDIE SOFIA: Ed Yong is a science writer and author of An Immense World– How Animal Senses Reveal the Hidden Realms Around Us. There’s an excerpt on our website if you want to take a look sciencefriday.com senses that’s sciencefriday.com senses.