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

by Ed Yong

Earth teems with sights and textures, sounds and vibrations, smells and tastes, electric and magnetic fields. But every animal can only tap into a small fraction of reality’s fullness. Each is enclosed within its own unique sensory bubble, perceiving but a tiny sliver of an immense world.

Instead, an Umwelt is specifically the part of those surroundings that an animal can sense and experience—its perceptual world.

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.

Each species is constrained in some ways and liberated in others. For that reason, this is not a book of lists, in which we childishly rank animals according to the sharpness of their senses and value them only when their abilities surpass our own. This is a book not about superiority but about diversity.

“They move finished and complete, gifted with extensions of the senses we have lost or never attained, living by voices we shall never hear,” wrote the American naturalist Henry Beston. “They are not brethren, they are not underlings; they are other nations, caught with ourselves in the net of life and time, fellow prisoners of the splendour and travail of the earth.”

Nothing can sense everything, and nothing needs to. That is why Umwelten exist at all.

The Umwelt concept can feel constrictive because it implies that every creature is trapped within the house of its senses. But to me, the idea is wonderfully expansive. It tells us that all is not as it seems and that everything we experience is but a filtered version of everything that we could experience.

There’s hardly a place you can touch a catfish without brushing thousands of taste buds. If you lick one of them, you’ll both simultaneously taste each other.[*32] “If I were a catfish, I’d love to jump into a vat of chocolate,” John Caprio tells me. “You could taste it with your butt.”

They eat meat, and if you put a piece anywhere on their skin (or add meat juices to the water around them), they’ll turn and snap at the right place. They’re exquisitely sensitive to amino acids—the building blocks of proteins and flesh.[*33] They aren’t great at detecting sugars, though: Unfortunately for Caprio, his chocolate fantasy would be underwhelming.

They are special because they keep hold of their target molecules, and because those molecules absorb light. This is the entire basis of vision. This is how all animals see—using light-sensitive proteins that are actually modified chemical sensors. In a way, we see by smelling light.

Dogs can detect the scent of shed skin, but for reasons that no one understands, the living snakes are undetectable to their noses.

The olfactory bulb might not even be necessary for smell. In 2019, Tali Weiss identified several women who seem to lack this structure altogether and could smell just fine. How they do it is anyone’s guess.

In September 2020, I noted that the army ant death spiral was the perfect metaphor for the United States’ response to the COVID-19 pandemic: “The ants can sense no picture bigger than what’s immediately ahead. They have no coordinating force to guide them to safety. They are imprisoned by a wall of their own instincts.”

For the longest time, researchers have claimed that the tongue delivers chemicals to the snake’s vomeronasal organ, also known as Jacobson’s organ, by threading its tips through two holes in the roof of a snake’s mouth. This is a myth. X-ray movies show that they do nothing of the sort, and the tongue simply nestles into the roof of the mouth. But to Schwenk’s eternal annoyance, the misconception still persists and abounds in textbooks.

“they may not be able to distinguish between sweet and savory.” Imagine being unable to tell the difference between soy sauce and apple juice.

Humans outshine almost every other animal at resolving detail. Our exceptionally sharp vision, Melin realized, gives us a rarefied view of a zebra’s stripes. She and Caro calculated that on a bright day, people with excellent eyesight can distinguish the black-and-white bands from 200 yards away. Lions can only do so at 90 yards and hyenas at 50 yards. And those distances roughly halve at dawn and dusk, when these predators are more likely to hunt. Melin was right: The stripes can’t possibly act as camouflage because predators can only make them out at close range, by which point they can almost certainly hear and smell the zebra. At most distances, the stripes would just fuse together into a uniform gray. To a hunting lion, a zebra mostly looks like a donkey.[*10]

They punch their prey into submission. They punch anything that intrudes upon their burrows. They punch each other at first contact. Mantis shrimps throw punches like humans throw opinions—frequently, aggressively, and without provocation.

(This is also why devices that claim to repel pests with ultrasound don’t really work: Their range is far too limited to be of much practical use.)

Bats are fully capable of avoiding such errors. They’re just not paying attention. They’re relying on memory and instinct. Humans behave in the same way: Most car accidents occur close to home, in part because drivers are less watchful when going down familiar routes. In both cases, perception is influenced not just by information from sense organs but also by what brains decide to do with that information.

Since at least 1749, there have been anecdotes about blind people who could walk unassisted through crowded streets, or (in later centuries) cycle around obstacles and skate in busy rinks. Humans had been echolocating for hundreds of years before anyone had even defined echolocation as a concept.

“Human biosonar has been dismissed as too crude to be worthy of study.” I suspect that’s because blindness still carries so much stigma. To be blind to something is to be oblivious to it. To have a blind spot is to have a zone of ignorance. To lack vision is to lack creativity. These ableist phrases equate lack of sight with lack of awareness. And yet blind people are profoundly aware of their surroundings.

“There is active resistance to blind people teaching other blind people how to be blind,” he tells me. “It’s a sort of reinforced custodialism.” Kish says that many blind children will naturally try to explore through noise. If they’re not using their tongues, they might snap their fingers or stomp their feet. But parents often see these behaviors as weird or antisocial, and put a stop to them before they can bloom into a sophisticated sonar sense.

Neuroscientist Lore Thaler has worked with Kish since 2009. Using brain scanners, she has shown that when he and other echolocators hear echoes, parts of their visual cortex—the region that normally deals with vision—are highly active.

This doesn’t mean Kish is “seeing” echoes. It’s more that he’s organizing the information from those echoes to build a spatial map of his surroundings—a task that vision naturally excels at. Without vision, the brain can still construct similar maps by repurposing the so-called visual cortex into an echo-processing cortex.