Meet the miniature water bear: nature's ultimate survivor or an alien from another planet?

IMAGINE living for more than 200 years, surviving trips to space and remaining unruffled by the most extreme conditions on the planet. Impossible?

tardigrade water bear

IMAGINE living for more than 200 years, surviving trips to space and remaining unruffled by the most extreme conditions on the planet. Impossible?

Impossible for you or me, but just everyday existence for incredible tiny, water-dwelling animals known as tardigrades, the hardiest creatures on Earth you've never heard of.

Resembling miniature underwater caterpillars, tardigrades boast teeny claws at the end of their legs, hence their "water bear" nickname.

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Also known as moss piglets, the eight-legged underwater critters grow no longer than 1mm, but can be seen with a basic microscope if you know where to look.

World's toughest critter: tardigrades may not be much to look at, but they are hard as nails. Photo: Getty Images

Lumbering around with a slow, almost bear-like gait over mosses, lichens and sand grains, the more than 900 species of tardigrades mostly live in freshwater, though about 10 per cent live in the sea.

They are found as far afield as the high Himalaya and the punishing Sahara desert, from the tropical Amazon to the freezing waters of the Arctic.

World's toughest critter: tardigrades may not be much to look at, but they are hard as nails. Photo: Getty Images

Incredibly, by entering a cryptobiosis state - effectively suspending their metabolism to enter a deathlike state - tardigrades are able to resist environmental conditions that would be lethal to humans.

tardigrade water bear

In the 1920's a German professor found that tardigrades are able to survive being boiled at 150 degrees celsius and being chilled for days at minus 200 degrees. They also shrug off doses of radiation that would kill humans: these are seriously tough little monsters.

In 2007 a team of crack tardigrade astronauts were launched into space by the European Space Agency. Surviving the vacuum and cosmic rays, some even survived deadly levels of solar UV radiation more than 1,000 times higher than on the surface of the Earth.

Scientists don't know how tardigrades evolve or who they are related to: only that they can survive a thousand atmospheres of pressure, x-rays and vacuums devoid of air.

Perhaps these creatures that can withstand trips to space actually came from beyond our solar system?

World's toughest critter: tardigrades may not be much to look at, but they are hard as nails. Photo: Getty Images

Simon Crerar is News Limited's Visual Story Editor, follow him at twitter.com/simoncrerar