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.