Usually, when you think about what could survive a nuclear war, you'd probably think of two things: cockroaches and Twinkies. But there's also this little guy:

This chubby little beetle is called a tardigrade (pronounced TAR-dee-grade), or more commonly, a "water bear," and it's nearly indestructible.

Teeny-tiny protostomes

Though the name "water bear" might conjure up images of a grizzly going for a swim, these animals are actually teeny-tiny protostomes, meaning that they're in the same family as pill bugs, centipedes, and lobsters. Like those animals, tardigrades are covered by a flexible cuticle shell made from chitin, similar to the stuff our fingernails are made from. The biggest tardigrades can get to be a whopping 1.5 millimeters long—about the size of a poppy seed—though most are too small to be seen with the naked eye. They've also been bumbling adorably around our planet for roughly 530 million years, making them one of the oldest organisms you can try to find in your backyard.

The "water bear" name actually comes from 18th century German zoologist Johann Goeze, who observed them in motion and thought that the way they ambled side to side was much like a bear on four pairs of pudgy legs. Check them out in the video above. What do you think?



Where do these little guys live?

Water bears can typically be found around water, as their name implies. Different species of tardigrades have been found in both saltwater and freshwater, making them pretty widespread throughout the world.

Generally, they gather themselves in damp plant matter, like lichens, mosses, or soil, which gives them their other nickname: moss piglets. They use their razor-sharp mouths (called "stylets") to pierce the plant cell's walls and suck nutrients out, similar to the way you'd drink from a juice box. And, just like other bears, they enjoy the thrill of the hunt: tardigrades have been known to eat other, smaller microorganisms (nematodes and rotifers) that share their mossy home.

Some tardigrades are a little more adventurous and have been caught napping under ice floes and diving into boiling hot springs.

Surviving the extremes

Water bears are the nigh-indestructible rock stars of the invertebrate world. Curious scientists have subjected tardigrades to a variety of experimental conditions, from immersing them in liquid nitrogen to exposing them to intense radioactive waves thousands of times stronger than what the normal human would be able to withstand. They can also be dropped in boiling water and emerge relatively unscathed.

They've even been sent into the cold, dark vacuum of outer space. In 2007, researchers stuck a few brave water bears to the outside of a space satellite for 10 days to see how they'd survive both the airless conditions and the sun's ultraviolet radiation. Upon their return back to earth, they were A-OK.

One note: though many news sources refer to tardigrades as "extremophiles," the moniker isn't entirely accurate. These little bears can survive under extremely harsh conditions, but they don't purposefully seek them out. As you can imagine, they'd much prefer to hang out around a freshwater pond than around a boiling hot spring.



How is this all possible?

Tardigrades have a pretty neat trick for dealing with extreme conditions. Just like a bear, they can enter a state of hibernation. This state is called "cryptobiosis," during which their metabolism s-l-o-o-o-w-s d-o-o-o-w-n to about 0.01% of what it initially was. During this state, they also dry themselves out, wringing out 95% of their body's water, like you might do with a towel. Finally, they tuck their heads down, fold in their legs, and begin producing a waxy outer secretion for protection.

The resulting animal produced by this transformation is like a curled, crispy tardigrade chip and is called a "tun."

While tardigrades might start off as chubby bear look-alikes, their tun counterparts are surprisingly hardy. The secret here is in their dehydration. Researchers have discovered that some forms of damage—like freezing and radiation—need water within the cells to enact their damaging effects. Dehydration also protects against boiling temperatures by preventing intracellular water from turning into steam, which might otherwise damage cells.

And tuns have another trick up their tiny sleeves: producing a specific form of sugar, known as trehalose. Though the verdict's still out on how this sugar protects the tardigrade's integrity, some ideas have popped up, proposing that molecules of the sugar can form hydrogen bonds on cell surfaces to replace the body's lost water, forming a gel that protects the tardigrade's cells from being deformed as they would under other dehydrating conditions.

Once in this dried-out state, tardigrades can survive for nearly a decade. When conditions become a little more friendly (and wet), the water bear can spring back to life and continue to bumble along adorably.

Awesome survival skills aside, there’s no question that these little beasties are the cutest moss dwellers I’ve ever seen – spiny mouth and all.

Ed note: This post was updated August 11 to remove some since-disproven studies about the tardigrade's genome.