What is a cold-blooded animal?


A cold-blooded, or ectothermic, animal is one that does not have an internal mechanism to regulate body temperature. Instead, a cold-blooded animal relies on solar energy captured by the environment. Reptiles, amphibians and fish are examples of cold-blooded animals.


Reptiles often expose themselves to the sun on rocks to absorb the heat. The heat increases the reptiles’ metabolism, which results in an active period. If the weather is very hot, a reptile may burrow into the sand or seek shade in a hollow or some other cool shelter. In this way, the behavioral instincts of the cold-blooded animal keep its body temperature within the proper range. As the ambient temperature drops, the animal’s metabolism slows down to conserve energy.

fish and amphibians

An alligator.

Regarding their environments, amphibians and fish have similar behaviors. A frog that gets too hot on the muddy banks of a river will burrow into the soft earth or look for a cooler place in the water. Fish change depths to regulate their temperature, seeking out cooler, deeper water or warmer water that is closer to the surface.

power requirements

Snakes are cold-blooded.

A cold-blooded animal does not use internally generated energy to regulate its body temperature, so it requires much less energy than warm-blooded, or endothermic, animals. Warm-blooded animals such as humans, other mammals and birds have internal mechanisms that keep their body temperature within a certain range regardless of the surrounding ambient temperature. This self-regulation requires a lot of energy, obtained through frequent meals. A cold-blooded animal doesn’t need to eat as often and can eat a meal every few weeks. As a result, cold-blooded animals are able to thrive in remote areas, such as small islands and deserts, where food is too scarce to sustain warm-blooded animals.

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Brain Power

Like all amphibians, salamanders are cold-blooded animals.

The brains of cold-blooded animals tend to be less complex and use less energy. At the same time, dinosaurs were assumed to be cold-blooded, slow-moving, and stupid animals. More recent research indicates that many species of dinosaurs, such as Tyrannosaurus rex, were fast and quite intelligent, leading some scientists to assume that dinosaurs were warm-blooded.

The case of the wood tree frog

Cold-blooded animals tend to thrive in remote locations such as small islands.

Cold-blooded animals can do some unusual things as a result of their physiology. For example, in winter, a wood tree frog burrows under the earth or leaves and freezes almost completely with the ground. Its heart and brain functions cease, and the frog’s eyes turn milky white. It appears to be as solid as an ice cube, but when the temperature rises, the frog comes back to life as it thaws. The frog’s brain and heart work again to start the rest of its body, and eventually it is able to jump away.

Research shows that the starches that the frog consumes just before the period of stasis are converted into glucose, or blood sugar. This makes it more difficult for the fluid to crystallize in the frog’s cells, so it acts as a sort of biological antifreeze. The wood frog’s cells never fully freeze, so it is able to thaw without damage.


Other frog species survive months of drought by burying themselves and entering a state known as estivation or estivation, returning to the surface when the rains come. Although they are completely dormant for months, these animals do not lose muscle mass. Scientists believe that a greater understanding of this capability could lead to applications in healthcare and space travel.

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