What does the camel store in its hump?

Camels do not store water in their humps, as it is commonly believed. The humps are actually reservoirs of fatty tissue. Concentrating body fat in their humps minimizes heat-trapping insulation throughout the rest of their body, which may be an adaptation to living in hot climates. When this tissue is metabolized, it acts as a source of energy and yields more than 1g of water for each 1g of fat converted through reaction with oxygen from air.