Here are 7 incredible things we learned this year that animals can do

From powerlifting to growing an entirely new body, these are the capabilities that most impressed us

photo of a sea slug body next to its detached head

The detached head of an Elysia sea slug crawls by its leaf-shaped body a day after separation. The detached head will grow an entirely new body.

Sayaka Mitoh

This year, animals of all shapes and sizes surprised us with amazing abilities we didn’t know they had. From powerlifting to walking on the underside of water, these are the creature capabilities that most impressed us in 2021.

Sea slugs that grow new bodies

In a spectacular feat of whole-body regeneration, some Elysia sea slugs can grow a new body from just the head (SN: 4/10/21, p. 4). This feat may come in handy when animals are riddled with parasites and need a fresh start. The head simply detaches itself, crawls away and regrows an entirely new body, including the heart. These are the only animals with a heart that are known to regenerate so much of themselves.

To document the extreme regeneration of an Elysia sea slug, researchers tied a leash around a natural groove in a sea slug’s neck. The sea slug escaped by discarding most of its body. While the headless body died, the head regenerated the rest of the body within 17 days.

Squirrels that parkour

We’ve all seen squirrels pull off death-defying maneuvers, but now we know more about how the rodents pull off their stunts. Like masters of parkour — the sport in which people leap, bounce and climb through an obstacle course — squirrels gauge the bendiness of branches when jumping. The rodents also use parkour-style jumps off of vertical surfaces to slow down and stick landings, researchers found (SN: 8/28/21, p. 14).

Researchers trained squirrels to jump through an artificial forest obstacle course to study how they leap from branch to branch without falling. High-speed camera footage showed that squirrels can learn to stick landings in just a few jumps and consider both branch bendiness and distance when deciding to leap from a limb.

Animals that eat surprising animals

This year upended notions of predator and prey, revealing animals making meals of one another in surprising ways. Researchers found that more than 40 species from 11 families of spiders eat snakes, using sticky silk and venomous bites to subdue serpents up to 30 times their size (SN Online: 8/4/21).

photo of a spider with a snake caught in its web
A brown widow spider inspects a common garter snake trapped in a web.JULIA SAFER

What’s more, one Seychelles giant tortoise apparently didn’t get the memo that tortoises are gentle herbivores. It was spotted stalking, catching and eating a bird chick whole, the first documented example of a tortoise hunting prey (SN: 9/25/21, p. 5).

In the Seychelles, an archipelago off the coast of East Africa, a tortoise — usually a strict herbivore — hunted, killed and ate a young bird that fell from its nest.

A beetle that walks on water, underwater

A water strider’s ability to walk on water is incredible enough, but the tiny water scavenger beetle flips the script: It walks on water upside down, clinging to the water’s surface from below (SN: 7/31/21, p. 13). The insect may use a small air bubble to pin its belly to the underside of the water’s surface, but just how it steps without breaking the water’s surface tension remains a mystery for now.

An aquatic beetle walks along the underside of the water’s surface. The thin bubble visible along the insect’s belly may help pin it to the surface and provide a source of oxygen.

A bird that mimics a flock

The male superb lyrebird lives up to its name with its excellent vocal abilities, mimicking nearly any sound it hears in its Australian forest home — even chainsaws and cameras. Now scientists have recorded the bird mimicking the sounds of several other bird species at once — replicating an entire soundscape. It’s the only known animal with this talent (SN: 3/27/21, p. 12). Because the lyrebird mimics multiple alarm calls in particular, researchers aren’t sure if it’s also trying to sound an alarm or just showing off for mates.

At the close of trying to impress a female with an elaborate song and dance, the male lyrebird adds a remarkable flourish. Its voice re-creates the alarmed chirps and wingbeats of many birds of different species, a degree of mimicry prowess never seen before in birds.

Spiders that lift prey up to 50 times their own weight

In an innovative take on a pulley system, some spiders, including black widows, can hoist heavy prey up, up and into their webs using only strands of their silk (SN: 2/27/21, p. 13). Researchers observed the spiders attaching strand after strand from their main web to large prey such as lizards, with each strand just a bit shorter than the last so that the stretchy silk slowly reeled in the prize.

Filmed in a lab box, a spider tries to capture a much bigger roach to feast on. The spider attaches one silk strand after another to the struggling roach until the silk supports all of the roach’s weight. Then the spider keeps adding shorter and shorter strands that tug the monster weight of the prey up toward the main part of the web.

Polar bears that wield weapons

In a macabre example of tool use by animals, polar bears sometimes kill walrus by bashing them with large chunks of stone or ice (SN: 8/28/21, p. 16). Inuit hunters have long reported polar bears attacking prey this way, and a review of historical and modern documentation confirms that stone-wielding polar bears are a real phenomenon. This puts polar bears on the list of tool-using animals, including crows, chimpanzees, elephants and, of course, humans.

sketch of a polar bear pushing a rock over a cliff to kill a walrus
In this illustration, which appears in an 1865 book by adventurer Charles Francis Hall, a polar bear uses a rock as a tool to kill a walrus. Some have thought that Inuit reports of this behavior were just stories, but research from this year suggests not.C.F. HALL, LIBRARY OF CONGRESS

Erika Engelhaupt is a freelance science writer and editor based in Knoxville, Tenn.

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