Do camels really have water in their humps?

To survive in the desert, camels store water in their humps, right? Not quite. Although camels do have tricks to make the most of water they find, their humps aren't one of them. So why do camels have humps on their backs?

The answer: fat storage. 

"They deal with dry seasons when food and water is scarce," said Rick Schwartz, an animal care supervisor and national spokesperson at the San Diego Zoo. When food is available, camels eat enough calories to build up their humps so they can survive long periods of time when food is scarce. With a "full" hump, a camel can go up to four or even five months without food, Schwartz said. When camels use up their fat, their empty humps flop over like a deflated balloon until they eat enough to "inflate" them again, Schwartz said.

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Camel calves aren't born with these fat deposits and don't grow them while they are nursing. "All the energy they're getting from mom is going to the growth of the body," Schwartz told Live Science. Young camels begin to wean when they are 4 to 6 months old, although their humps don't start to form until they are 10 months to a year old. "But as the wild camels are dealing with the cycles of the seasons, they need to have some sort of hump within that first year," Schwartz said. "They have to make it through that first dry season."

There are two species of camels. Bactrian camels (Camelus bactrianus) live in parts of western China and Central Asia, and they have two humps. Arabian camels (Camelus dromedarius) are more common and have only one. But as far as Schwartz is aware, the extra hump does not allow Bactrian camels to go longer without food.

Although many animals store fat around their stomachs and sides, camels pack on the pounds vertically. One theory is that camels have a stomach callus which they lay directly in the sand, and belly fat could make it harder to lay this way, Schwartz said. Another theory is that being tall and narrow, with fat stored in humps instead of around the sides, means camels are exposed to less sunlight and less heat.

Because camel humps store food, the dromedaries need other ways to cope with water scarcity. For example, camels can can drink up to 30 gallons (114 liters) of water in one sitting, they excrete dry feces to retain water, and their kidneys efficiently remove toxins from water in the body so they can retain as much as possible, Schwartz explained. Camels have several other ways to make each drink of water go far, such as by catching moisture from every breath they exhale through their nose. 

This incredible ability to make do with less water is "probably why the myth came about that if they go so long without water, they must be storing water in the humps," Schwartz said.

Originally published on Live Science.