Here are a few excerpts from a book I recently read, "An Immense World: How Animal Senses Reveal the Hidden Realms Around Us," by Ed Yong.
This was a radical notion at the time—and in some circles, it might still be. Unlike many of his contemporaries, Uexküll saw animals not as mere machines but as sentient entities, whose inner worlds not only existed but were worth contemplating. Uexküll didn’t exalt the inner worlds of humans over those of other species. Rather, he treated the Umwelt concept as a unifying and leveling force. 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.
There’s always at least one person who writes in with a pompous and incorrect corrective, so let’s get this out of the way: The word octopus is derived from Greek and not Latin, so the correct plural is not octopi. Technically, the formal plural would be octopodes (pronounced ock-toe-poe-dees) but octopuses will do.
This goes against every stereotype one might have about crocodiles as brutish, unfeeling animals. With jaws that can crush bone and thick skin that’s heavily armored with bony plates, they seem like the antithesis of delicacy. And yet, they are covered head to tail in sensors that, as Ken Catania and his student Duncan Leitch showed, are 10 times more sensitive to pressure fluctuations than human fingertips.
This dependency on vibrations is so absolute that many animals can exploit orb-weavers by camouflaging their footsteps. The small dewdrop spider Argyrodes is a thief, stealing from larger spiders like Nephila by hacking their webs. From a nearby hiding place, it runs several lines of silk over to the hub and spokes of a Nephila web, effectively plugging its sensory system into that of the bigger spider. It can tell when Nephila has caught something and is wrapping it in silk for storage. It then runs over and eats the insect itself, often after cutting it free from the main web so that the host spider can no longer detect it. Argyrodes acts carefully to avoid creating its own telltale vibrations. It runs only when Nephila is moving and treads more slowly when Nephila is still. It also holds on to any strands it cuts to avoid any sudden releases in tension. Through such subterfuge, this thief is almost never caught. As many as 40 of them might be plugged into a single Nephila web.
Echolocation differs from the senses we have met so far, because it involves putting energy into the environment. Eyes scan, noses sniff, whiskers whisk, and fingers press, but these sense organs are always picking up stimuli that already exist in the wider world. By contrast, an echolocating bat creates the stimulus that it later detects. Without the call, there is no echo. As bat researcher James Simmons explained to me, echolocation is a way of tricking your surroundings into revealing themselves. A bat says, “Marco,” and its surroundings can’t help but say, “Polo.” The bat speaks, and a silent world shouts back.
Many animals, including salmon, turtles, and Manx shearwaters (a kind of seabird), can also imprint on the magnetic signature of their birthplaces, etching it deep within their memory so they can find the same sites as adults. Turtles use these imprints to lay eggs on the same beaches from which they hatched. Their accuracy is uncanny. Green turtles that nest on Ascension Island can find that same tiny nub of land in the middle of the Atlantic after a 1,200-mile journey to and from Brazil. This “natal homing” instinct is so strong that turtles will sometimes swim for hundreds of miles to their beach of birth, even though there’s a perfectly good alternative right next to them.[*9] Perhaps that’s because good nest sites are hard to find. They must be accessible from the water. The sand grains must be large enough to let oxygen through. The temperature must be exactly right, since turtles develop as males or females depending on how hot or cold their eggs are. “A turtle might say: Well, the one place in the world I know works is the beach where I developed myself,” Lohmann says. And its magnetic map allows it to relocate that sure-bet nursery after years away at sea.
In 2001, when astronomer Pierantonio Cinzano and his colleagues created the first global atlas of light pollution, they calculated that two-thirds of the world’s population lived in light-polluted areas, where the nights were at least 10 percent brighter than natural darkness. Around 40 percent of humankind is permanently bathed in the equivalent of perpetual moonlight, and around 25 percent constantly experiences an artificial twilight that exceeds the full moon. “ ‘Night’ never really comes for them,” the researchers wrote. In 2016, when the team updated their atlas, they found that the problem was even worse. By then, around 83 percent of people—and more than 99 percent of Americans and Europeans—were living under light-polluted skies. Every year, the proportion of the planet covered by artificial light gets 2 percent bigger and 2 percent brighter. A luminous fog now smothers a quarter of Earth’s surface and is thick enough in many places to blot out the stars. Over a third of humanity, and almost 80 percent of North Americans, can no longer see the Milky Way. “The thought of light traveling billions of years from distant galaxies only to be washed out in the last billionth of a second by the glow from the nearest strip mall depresses me no end,” vision scientist Sonke Johnsen once wrote.
