No Desert Too Dry
All living things need water--it's essential for the chemical reactions of life. But some creatures need only a little. Desert plants and animals thrive where there's less than 25 centimeters (10 inches) of rain each year. Animals may use certain physical features of their bodies to avoid wasting water, or certain behaviors, such as staying out of the sun. Plants, meanwhile, may store water in their tissues, or develop longer roots to tap water deep underground.
Life. Just Add Water
No bigger than a speck, tiny eight-legged creatures called tardigrades live either in ocean or freshwater habitats. If drought strikes, they essentially shut down their metabolism and shrivel up in a ball called a tun, waiting until water returns. They'll wait a long time-- as much as several years, in fact-- allowing them to survive better in unpredictable environments. Tardigrade tuns can also withstand oxygen deprivation and extreme heat or cold.
Doesn't Drink the Water
Is it possible to survive without drinking any water at all? Kangaroo rats prove that it is. Some species get all the water they need from the food they eat. Their kidneys help by recycling water more than four times as efficiently as human kidneys do. They also conserve what little water they do take in by keeping out of the sun during the daytime, emerging from their burrows to look for food after dark when temperatures drop.
A Breath of Dry Air
Camels don't store water in their humps--instead, their humps store fat. So, then, how do camels stay hydrated? Look into the nose of the camel's skull and you'll see one feature that helps them conserve water. The intricate surfaces that fill their nasal passages sponge up nearly all the moisture from the air they breathe out. Camels also can tolerate a much higher peak body temperature, 41 °C (106 °F), than most mammals. So when it's hot, they don't have to waste water by sweating.
Don't Call Me Cactus
The soft, spiny stems of this euphorbia plant might remind you of a cactus. Although cacti and many euphorbs evolved the same approach to living in the desert-growing spines for protection and storing water in their stems-they aren't closely related. These two groups of plants independently evolved the same strategies for coping with similar environments, an example of convergent evolution.