The (almost) indestructible water bear
Tardigrades, microscopic water-dwelling animals also known as water bears, are among the most famous survivalists in the world. Since they were first described by a German zoologist in 1773 they’ve been found in the depths of the ocean, at the top of Himalayan mountains, at the poles and in hot springs. Despite this amazing resilience, they’re technically not extremophiles. This classification is reserved for those creatures that exploit and thrive in extreme conditions, while tardigrades cope by suspending their metabolism and entering dormancy. During periods of drought, water content in the body drops to one per cent of the normal level. To prevent damage to the body, unique proteins take the place of lost water in the cells and become glass-like. In their dehydrated tun state some species of tardigrade are capable of enduring temperatures close to absolute zero and, though hot temperatures will eventually kill them, they can last for several minutes at 150 degrees Celsius. With their metabolism barely functioning, starvation can be endured for years. They can also survive radiation levels hundreds of times higher than the dose that would kill a human and have even returned alive from a journey to the vacuum of space. Many tardigrades can survive in this desiccated dormant state (known as cryptobiosis) for five years and will resume normal activity within hours of exposure to moisture. A few exceptional specimens have been ‘brought back to life’ after almost a decade, establishing tardigrades as some of the creatures most likely to survive a nuclear war or apocalyptic astrophysical event.