Read more: Extreme survival: The toughest life forms on Earth
Lots of animals sleep through dry spells, but to get through dry decades you have to turn your cells into sugar glass
Of all the limits on life, water is the least negotiable. All cells need water as a medium for their chemical reactions to take place in, and to keep their membranes intact.
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For most animals, drying out means certain death. A few life forms, however, can survive by hunkering down and waiting for the rains to come. Tardigrades, rotifers, nematode worms and the larvae of some shrimps and one fly dry up, roll into a ball and sit out the drought. Most lichens and mosses, some fungi and bacteria, and hundreds of species of flowering plants also dry up and wait for conditions to improve, sometimes for years or decades.
All of these organisms survive drying by replacing water molecules in and around the cell with sugars, which maintain the cell鈥檚 structure. As the sugar level in the cell increases it turns the cytoplasm from a liquid into a solid called sugar glass, freezing the cell in time.
鈥淭hese animals replace water molecules with sugar, turning their cytoplasm into a solid called sugar glass鈥�
It is a clever trick, but in the grand scheme of things, not a common one. Other methods of sitting it out are less drastic. For example, some toads and several species of frog, including the African bullfrog (Pyxicephalus adspersus), dig themselves into a hole, form a waterproof cocoon around their body leaving their nostrils free, and go into a state similar to hibernation until the rainy season comes. Countless other creatures, from snails to crocodiles, do something similar. Even a few mammals, including ground squirrels and one species of lemur, can sleep through the dry times.
For all these organisms, though, drying out and hiding are only temporary measures. Lack of water is the ultimate outer limit of life on Earth and, as most species have found, the best strategy is to avoid such areas in the first place.
