Tardigrades, or moss bears as they are sometimes called, are only about half a millimeter (0.02 inches) long. With their thick legs and round bodies, they look a bit like microscopic caterpillars.

But looks can be deceiving. While caterpillars are relatively fragile creatures, some tardigrades have survived in temperatures close to absolute zero (-272 degrees Celsius, or -458 degrees Fahrenheit), while others have survived scorching heat of as much as 150 degrees Celsius (300 degrees Fahrenheit).

They can also survive high levels of radiation, water pressure in the deepest abysses of our oceans, and in the vacuum of outer space. And as if that wasn't enough, they can also survive without food or water for more than 30 years - yes, years!

The tardigrade or "water bear" - among the cutest of microorganisms

Now, to be clear: tardigrades aren't extremophiles - they don't thrive under particularly hostile conditions, like some bacteria that really come into their own in highly acidic or near boiling water, or in rocks buried deep underground.

It's just that many things that kill almost anything else won't kill them. Thanks to this extraordinary resilience, the tiny critters are among a small group of species that have survived all five mass extinction events in the history of our planet.

In fact, a recent study indicated that this is the single animal most likely to survive until the end of life on Earth - that is, when the sun fails or engulfs the Earth, in about 10 billion years.

So where can you find such an extraordinary creature? Well, since very little can kill them, pretty much everywhere, really.

They have been found high up in the Himalayas, as well as deep down in the ocean; in frozen puddles in Antarctica, also in marshes at the equator; and there are probably a ton of them in the rain gutter of your house.

They particularly like to live in moss (hence the name moss bear), where as many as 200 of them can be found in one square centimeter.

They may be tiny - but given their resilient nature, tardigrades are likely to outlive us. And considering the havoc we've been wreaking on the planet, that could turn out to be their most impressive accomplishment of all.