Xerocole

A xerocole (), is a general term referring to any animal that is adapted to live in a desert. The main challenges xerocoles must overcome are lack of water and excessive heat. To conserve water they avoid evaporation and concentrate excretions (i.e. urine and feces). Some are so adept at conserving water or obtaining it from food that they do not need to drink at all. To escape the desert heat, xerocoles tend to be either nocturnal or crepuscular (most active at dawn and dusk). Xerocoles have developed a variety of mechanisms to reduce water loss via evaporation. Mammalian xerocoles sweat much less than their non-desert counterparts. For example, the camel can survive ambient temperatures as high as without sweating, and the kangaroo rat lacks sweat glands entirely. Both birds and mammals in the desert have oils on the surface of their skin to "waterproof" it and inhibit evaporation. Desert insects use a similar method, as their cuticles are waxy to prevent water from escaping; however, at critical temperatures (ex. for cockroaches), the wax molecules in the cuticle rearrange to become permeable and permit evaporative cooling. Amphibious xerocoles, such as species of the frog genus Phyllomedusa, have wax-like coatings on their skin to reduce water loss. The frogs secrete lipids from glands in their skin: when their skin begins to dry out, they move their limbs over the glands on their backs, and wipe the lipids over their bodies. Other desert amphibians, such as the frog genus Cyclorana, avoid desiccation by burrowing underground during dry periods and forming a cocoon from shed skin: rather than being sloughed off, the skin remains attached to create the cocoon. As skin layers amass, water impermeability increases. Though desert birds lack sweat glands, they can still take advantage of evaporative cooling by panting, which cools the trachea and lungs, and gular flapping, which consists of rapidly fluttering the gular skin to move air over the inner mouth and throat. Kangaroo rats and other small mammals use evaporative cooling in a similar way.