Imagine that you take a walk around your yard or nearby park and, immediately, the sounds of an insect orchestra surround you.
Produced by the muscular movements of sap-feeding insects called treehoppers, this imagined soundscape emerges from vibrations that flow across the surface of plants. But it is not at all like the familiar vocalizations of crickets or cicadas; instead, it's something richer, more varied. Some sounds are song-like, others akin to the noises of machines or musical instruments. The noise emitted from even a single plant may be "as raucous as a busy street."
In An Immense World: How Animal Senses Reveal the Hidden Realms Around Us, Pulitzer prize-winning science journalist Ed Yong explains that, on a real walk instead of this one we've imagined, humans would not be able to hear the treehoppers' music without special equipment. In the company of scientists with a laser vibrometer, a device that converts the treehopper vibrations into sounds audible to human ears, Yong gets to hear them in the wild and in the laboratory. He is "dumbfounded" by the "haunting, mesmerizing" sounds.
In this book that follows on from 2018's I Contain Multitudes, Yong writes in a perfect balance of scientific rigor and personal awe as he invites readers to grasp something of how other animals experience the world. Communicating through surface vibrations is a mighty cool example that extends beyond treehoppers to elephants and spiders, and to this fact about frogs: Attuned to vibrations entering the eggs, frog embryos hatch quickly if a snake shows up with a hard bite, but ignore rain, wind, footsteps and even an earthquake. "They have agency," Yong writes. "They have an Umwelt."
Made famous by zoologist Jakob von Uexkull in 1909, the term Umwelt refers to the perceptual world experienced by each animal, a highly specific kind of "sensory bubble." When we walk our dog and she stops to smell every other bush or car tire, she's taking in through her acutely sensitive nose smells that we take in faintly or not at all. That's because humans and dogs have two different sensory bubbles, or Umwelten.
Yong explores the animals' Umwelten through chapters devoted, in addition to surface vibrations, to smells and tastes; light; color; pain; heat; contact and flow; sound; echoes; electric fields; and magnetic fields. The concluding two chapters then discuss how senses work together, and how a single species, ours, has disrupted animal senses through light and noise pollution. Gradually, the theme Yong establishes at the start gains shape and dimension as he writes that our own Umwelt feels natural, but it's only one way to sense the world:
"It is all that we know, and so we easily mistake it for all there is to know. As a result, we tend "to frame animals' lives in terms of our senses rather than theirs."
Yong is indifferent to two motivations that compel scientists to study animal senses: to better understand our own senses and to apply knowledge of animals' senses to produce new technologies. I found his perspective welcome: "Animals are not just stand-ins for humans or fodder for brain-storming sessions. They have worth in themselves."
Did you know that most insects are deaf? That the visual fields of cows, who may seem to show a fixed gaze to the point of being indifferent to the environment, wrap around in space so that cows can see in front, to the side, and behind them all at once? Or that the only sense that exists without an associated organ of some sort is magnetoreception, used by green sea turtles who "read" Earth's magnetic fields as they return to their nesting grounds on a small island after traveling 1,200 miles away?
Magnetoreception is a sense humans (apparently) use rarely, while some animal sensory capacities are unavailable to us altogether. Certain electric fish "can work out the position, size, shape, and distance of the objects" near them by creating "electric images... from patterns of voltage dancing across" their skin. Dolphins navigate by listening for echoes of their click sounds:
"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. It can almost certainly tell different [fish] species apart based on the shape of [their] air bladders."
(This isn't to say that humans can't echolocate at all. Yong takes a walk with Daniel Kish, who had both eyes removed in early childhood owing to aggressive cancer. As Kish strolls, bikes, or hikes, he emits clicks that allow him to sense, through echoes, the location and shapes of everything from houses and cars to trees. Still, even the best human echolocators can't do what dolphins can do.)
My admiration for the book is, well, immense. I do wonder about one choice that Yong makes, evidenced in some examples above and in sentences like this one: "A dolphin is an echolocator that clicks with its nose and listens with its jaw." Here, the word "it" is better suited to an object, rather than a living, thinking being, and the same with the word "that." An alternative sentence, "Dolphins are echolocators who click with their noses and listen with their jaws," seems to me more aligned with Yong's evident regard for animals as valuable beings in their own right. As Scott Simon wrote last year for NPR, "If a cat or dog shares your domicile, I'll venture a guess that you don't refer to the four-footed family member who licks your face, naps in your lap, sleeps on your bed... as 'it.'" Full disclosure: I was a signatory to letter described by Simon asking for the media to use more respectful pronouns for animals.
With our insistence on bright lights that disrupt dark skies, and a way of life that produces incessant noise from all sorts of machines including on land, air, and sea highways, we are seriously harming other animals' abilities to use their senses properly. But there's hope, because "sensory pollution is an ecological gimme": Conditions improve immediately when lights or engines are shut off or adjusted. By extinguishing lights that disrupt the paths of migrating birds and sea turtles, and by muffling noise through use of sound barriers, we can protect the glorious Umwelten all around us.
Like many thousands of other people, I have relied throughout the course of COVID-19 on Yong's reporting at The Atlantic as he cracked open the fast-changing world of pandemic science. Now, with An Immense World, Yong brings into beautiful focus a host of other animal sensory worlds that co-exist with ours, and how we may protect them. He has synthesized and compellingly presented a spectacular amount of scientific information to do this, making it look easy along the way. But isn't easy at all. It's a magnificent achievement.
Barbara J. King is a biological anthropologist emerita at William & Mary. Animals' Best Friends: Putting Compassion to Work for Animals in Captivity is her seventh book. Find her on Twitter @bjkingape