What Is in a Camel's Hump? Fat, Water Myths and Energy

What is a camel’s hump made of?

Inside the hump there is no bone, no muscle used for movement and no water bag. It is a mass of fatty (adipose) tissue bound together by tough fibrous connective tissue, sitting on top of the spine and covered by skin and hair. The size of the hump depends almost entirely on how well the camel has been eating.

The dromedary camel has one hump, at least 20 cm (8 in) tall in a healthy adult. The Bactrian camel of Central Asia has two humps, one over the shoulders and one over the hips, and both are made of fat in the same way. In the wild Bactrian camel the humps are smaller and more cone-shaped than in its domestic cousin.

How the hump works as an energy store

When grazing is good, a camel eats more than it needs and turns the surplus into fat in the hump. When it later crosses a stretch of desert with little food, it breaks that fat down to fuel its body. This lets camels keep walking and carrying loads for days on poor food.

You can read a camel’s condition from its hump:

• Full and upright: the camel has been eating well and has reserves to spare.
• Small and soft: the camel has been using its reserves.
• Leaning or flopped to one side: the camel has used up much of its fat, a sign of hunger.

When the camel eats well again, the hump slowly rebuilds. Herders in Africa and Asia have long judged their animals by the state of their humps, and a big, firm hump is seen as a sign of a healthy camel.

Why is fat stored on the back?

Most mammals store fat under the skin all over the body. For a desert animal that would be a problem, because a layer of fat insulates the body like a blanket and makes it harder to get rid of heat.

By packing most of its fat into one lump on the back, the camel leaves the rest of its skin free to lose heat to the air, especially on its belly and legs. This fits with the camel’s other cooling tricks, such as letting its body temperature rise by several degrees during the day instead of sweating.

The water myth: can the hump give a camel water?

The idea that the hump is a water tank is one of the best-known animal myths. It probably arose because camels can go so long without drinking, and the hump seemed the obvious place for a store.

There is a grain of truth in the story. When an animal burns fat, the chemical reaction produces water as well as energy; roughly 1.1 g of water is made for every gram of fat used. This is called metabolic water. In theory, 36 kg of fat could produce close to 40 liters (10 US gallons).

In practice the camel does not gain much from this. Burning fat needs oxygen, so the camel has to breathe more, and each breath carries moisture out of the lungs. The physiologist Knut Schmidt-Nielsen, who studied camels in the Sahara in the 1950s, concluded that the water lost through the extra breathing roughly cancels out the water produced. The hump is therefore best seen as a food store, not a water store.

Where does a camel really keep its water?

Camels store the water they drink in the same places as other mammals: in the blood, the fluid between cells and the cells themselves. What makes them special is how slowly they lose it and how much loss they can tolerate.

When a dehydrated dromedary reaches water, it can drink about 100 liters (26 US gallons) in around 10 minutes, rapidly refilling its body rather than its hump. More detail is in How long can a camel go without water?.

One hump or two?

The dromedary has one hump and both Bactrian species have two, but they are used in the same way. Hybrids between the two species, bred in Central Asia and Turkey, usually have one long hump with a dip in the front, or two humps of different sizes. A side-by-side look at both species is in dromedary vs Bactrian camel.

The other members of the camel family, the llamas, alpacas, guanacos and vicuñas of South America, have no humps at all. They live in cold, high mountains and grasslands rather than in hot deserts, and they store fat in the usual way, under the skin and around the organs.