They can survive temperatures ranging from 150°C to -272°C. They can go a decade without water. They can live virtually anywhere you can think of, from the highest mountains, underneath layers of solid ice, to the deepest ocean trenches. They can endure the most extreme conditions on Earth – and even beyond. But what are they?
Meet the tardigrades. They are also called water bears, presumably because if you squint hard enough they almost look like very obese bears with a few additional legs. They are very minute animals, rarely growing longer than 1.5mm, and they belong in their own phylum, meaning they are distinctly different from insects and other arthropods. Tardigrades are also eutelic, which means all members of the same species have exactly the same number of cells. Even young tardigrades that have just hatched have the same number as fully-grown individuals; the actual cells merely get bigger as the animals grow rather than going through cell division.
But tardigrades are most famous for their near indestructibility. They are so hardy, in fact, that scientists have performed a multitude of tests and experiments to see just what these animals can withstand. We now know that in addition to the temperature extremes mentioned above, tardigrades can handle 570,000 rads of x-ray radiation (a mere 2,000 rads would quite easily kill a human); they can withstand 6,000 atmospheric pressures, which is six times the pressure of the water in the deepest ocean abyss; they can be submerged in pure alcohol; and they can even survive being placed in liquid helium for a week.
That’s pretty much all of the extremes on the planet covered, but the tardigrades don’t stop there. We have even sent them into space, where they proved that they were capable of surviving temperatures perilously close to absolute zero, the empty suffocating vacuum and radiation so intense it would fry a human being. No other animal can survive such an ordeal.
So what is the tardigrades’ secret? How can they endure such extremes? It has everything to do with the fact that they can enter a state of suspended animation. If conditions become too disagreeable for a tardigrade, it simply gives up. It rolls into a ball and becomes completely inert. It covers itself in a protective wax and switches its metabolism off altogether. In this state, the tardigrade is as good as dead.
But it isn’t dead. If conditions one day improve – and that need only be a single droplet of water – the tardigrade simply revives itself and picks up where it last left off, even if ten years have passed in the interim. We often think of cockroaches as being almost impossible to kill, and tales of them being able to survive nuclear fallout are commonplace, but surely the true great survivors of the natural world are the tardigrades. Nothing else even comes close.