An Immense World: How Animal Senses Reveal the Hidden Realms Around Us

by Ed Yong

The human’s house might be bigger than the tick’s, with more windows overlooking a wider garden, but we are still stuck inside one, looking out.

Our Umwelt is still limited; it just doesn’t feel that way. To us, it feels all-encompassing. It is all that we know, and so we easily mistake it for all there is to know. This is an illusion, and one that every animal shares.

You could envision yourself with webbing on your arms or insects in your mouth, but you’d still be creating a mental caricature of you as a bat. “I want to know what it is like for a bat to be a bat,” Nagel wrote. “Yet if I try to imagine this, I am restricted to the resources of my own mind, and those resources are inadequate to the task.”

A scientist’s explanations about other animals are dictated by the data she collects, which are influenced by the questions she asks, which are steered by her imagination, which is delimited by her senses. The boundaries of the human Umwelt often make the Umwelten of others opaque to us.

When we pay attention to other animals, our own world expands and deepens.

many dog owners deny their animals the joys of sniffing. To a dog, a simple walk is an odyssey of olfactory exploration.

Such comparisons will always be flawed because smell is diverse and often unquantifiable. We need to stop asking “How good is an animal’s sense of smell?” Better questions would be “How important is smell to that animal?” and “What does it use its sense of smell for?”

An ant without olfaction is an ant without a colony, and an ant without a colony is barely an ant at all.[*18]

It turns out that the tongue’s tips splay out at the ends of each flick and get closer at the midpoint. This motion creates two donut-shaped rings of continuously moving air that draw in odorants from the left and right sides of the snake. It’s as if the snake temporarily conjures up two large fans that suck in odors from either side, concentrating diffuse odor molecules onto the tips of its tongue.

(We tend to wrongly equate taste with flavor, when the latter is more dominated by smell. That’s why food seems bland when you have a cold: Its taste is the same, but the flavor dims because you can’t smell it.)

most insects can taste with their feet and legs.

“We don’t have to look to aliens from other planets,” Jakob tells me. “We have animals that have a completely different interpretation of what the world is right next to us.”

Jakob’s colleague Nate Morehouse has shown that jumping spiders are born with their lifetime’s supply of light-detecting cells, which get bigger and more sensitive with age. “Things would get brighter and brighter,” Morehouse tells me. For a jumping spider, getting older “is like watching the sun rising.”

When a peregrine falcon dives after a pigeon, it doesn’t plunge straight at its prey. Instead, it flies along a descending spiral. That’s the only way it can keep the pigeon within its murderous side-eye, while also pointing its head down and maintaining a streamlined shape.[*20]

“Everyone asks us how we catch the killer flies,” Gonzalez-Bellido says. “You just move toward them slowly with a vial. If you’re slow enough, you’re just part of the background.”

Color exists in the eye of the beholder—and also in their brain.

Why we feel more relax when we see green color? Is it the wavelength itself that effects our brain or is it what we were conditioned to react or believe?

Color-blindness shouldn’t be a disability, but it can be because humans have built cultures that are predicated on trichromacy.

In fact, the opposite is true. Most animals that can see color can see UV. It’s the norm, and we are the weirdos.[*9]

Questions about what a scallop sees, or whether birds and humans see the same red, are philosophically interesting. But the distinction between pain and nociception is a morally, legally, and economically vital matter, which affects our cultural norms around catching, killing, eating, or experimenting on animals.

Could pain exist without consciousness? If you strip the emotion out of pain, are you just left with nociception, or a gray area that our imaginations struggle to fill?

When we ask if animals can feel pain, we’re asking less about the animals themselves, and more about what we can do to them. That attitude limits our understanding of what animals actually sense.

We project our senses onto theirs and assume that they’d be in discomfort because we’d be in discomfort.

With the lateral line, fish can feel the rich sources of information that are literally flowing around them. This awareness extends in almost all directions, for up to a body length or two away, which Dijkgraaf described as “touch at a distance.”

The tiger wandering spider doesn’t spin a web to catch food; instead, it sits in wait for its prey. Its legs are covered in hundreds of thousands of hairs, which are packed so densely that there can be 400 in a square millimeter. Almost all of them are connected to nerves and are sensitive to touch.

“The old people came literally to love the soil, and they sat or reclined on the ground with a feeling of being close to a mothering power…. This is why the old Indian still sits upon the earth instead of propping himself up and away from its life giving forces. For him, to sit or lie upon the ground is to be able to think more deeply and to feel more keenly; he can see more clearly into the mysteries of life and come closer in kinship to other lives about him. The earth was full of sounds which the old-time Indian could hear, sometimes putting his ear to it so as to hear more clearly.”

“I really respect the elephants. But I love the spiders. The fact that they’re so misunderstood by so many people just really makes me want to sing their praises so much more.”[*12]

In a very real way, the spider thinks with its web. Tuning the silk is like tuning its own mind.

Birds encode meaning in aspects of their songs that our ears can’t pick out and our brains don’t pay attention to. “Now, when I hear birdsong, I think it’s amazing that it sounds so complex but I’m still missing most of it,” Dooling tells me. “There’s a lot in there that another bird is appreciating that I can’t.”

If a dolphin echolocates on you, it will perceive your lungs and your skeleton. It can likely sense shrapnel in war veterans and fetuses in pregnant women.

When Eric Fortune collects electric fish from the wild, he can shine a flashlight upon them to no effect. But once he reaches into the water with a net, “if there is any exposed metal, you can’t catch them,” he tells me. Conductive metal is more of a beacon to them than actual light.

It turns out that all living things produce electric fields when submerged in water.

Spider silk picks up a negative charge as it leaves a spider’s body, and is repelled by the negatively charged plants on which they sit. That force, though tiny, is enough to launch the spider into the air.

Magnetoreceptors are “the holy grail of sensory biology,” Eric Warrant tells me. “There may even be a Nobel Prize in finding them.”

Corollary discharges explain why you can’t tickle yourself: You automatically predict the sensations that your writhing fingers would produce, which cancels out the actual sensations that you feel.

Animals cannot make sense of what’s around them without first making sense of themselves. And this means that an animal’s Umwelt is the product not just of its sense organs but of its entire nervous system acting in concert.

You can’t simply imagine how a human mind would work in a bat’s body or an octopus’s, because it wouldn’t work.

To stand any chance of knowing what it is like to be another animal, we need to know almost everything about that animal. We need to know about all of its senses, its nervous system and the rest of its body, its needs and its environment, its evolutionary past and its ecological present.

We are closer than ever to understanding what it is like to be another animal, but we have made it harder than ever for other animals to be.

As we push animals away, we get used to their absence. As the problem of sensory pollution grows, our willingness to address it subsides.