Fact Checked

What is a Cold Blooded Animal?

R. Kayne
R. Kayne

A cold blooded animal, or ectotherm, is one that does not have an internal mechanism for regulating its 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 will often sun themselves on rocks to absorb heat. The heat raises the metabolism of the reptiles, which results in an active period. If the weather is too warm, a reptile might bury itself in sand or seek shade in a hollow or some other cool shelter. In this way, the cold blooded animal's behavioral instincts keep its body temperature within the proper range. As ambient temperature drops, the animal's metabolism slows to conserve energy.

Fish and Amphibians

An alligator.
An alligator.

Relative to their environments, amphibians and fish have similar behaviors. A frog that gets too warm on the muddy banks of a river will either bury itself in the soft earth or seek a cooler spot in the water. Fish will change depths to regulate their temperature, seeking either cooler deeper water or warmer water that is closer to the surface.

Energy Requirements

Snakes are cold blooded.
Snakes are cold blooded.

A cold blooded animal does not use internally generated energy to regulate its body temperature, so it requires far less energy than warm blooded animals, or endotherms. Warm blooded animals, such as humans, other mammals and birds, have internal mechanisms that maintain their body temperature within a certain range, regardless of the ambient temperature of surroundings. This self-regulation requires vast amounts of energy that is obtained through frequent meals. A cold blooded animal doesn't need to eat as often and might eat one 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 support warm blooded animals.

Brain Power

Like all amphibians, salamanders are cold blooded animals.
Like all amphibians, salamanders are cold blooded animals.

The brains of cold blooded animals tend to be less complex and use less energy. At one time, it was assumed dinosaurs were slow-moving, dim-witted cold blooded animals. More recent research indicates that many species of dinosaurs, such as the tyrannosaurs rex, were fleet-of-foot and quite intelligent, leading some scientists to hypothesize that dinosaurs were warm blooded.

The Case of the Wood Tree Frog

Cold blooded animals tend to thrive in remote locations like small islands.
Cold blooded animals tend to thrive in remote locations like small islands.

Cold blooded animals can do some unusual things as a result of their physiology. For example, in winter, a wood tree frog will bury itself under dirt or leaves and freeze virtually solid with the soil. Its heart and brain functions cease, and the eyes of the frog turn milky white. It appears to be as solid as an ice cube, but when the temperature warms, the frog comes back to life as it thaws. The frog's brain and heart kick back in to jump-start the rest of its body, and eventually, it is able to hop away.

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


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

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Discussion Comments


I don't understand why people take cool blooded animals like reptiles as pets.

If these animals in nature, they will be fine because they will change their location and take advantage of the sun to regulate their temperature. If you put a cool blooded animal in a cage and in a certain spot, you will prevent them from maintaining the temperature they need.

I know people don't mean any harm, but cool blooded animals are different, they can't live the way dogs and cats do.


@anon125076-- Don't do that. Putting a blanket over an iguana will not provide warmth, it will do the opposite and keep the iguana cool. Iguanas are cold blooded so they need an outside heat source. You can use a heating pad and put it underneath the iguana so it can absorb the heat.


I wish we were also cold blooded. I know we wouldn't be as intelligent if we were, but just look at all the amazing things that cold blooded animals can do. They are definitely more prepared for survival than we are.

Warm blooded animals are so feeble when compared to cold blooded animals. We can control our internal temperature but we also have to eat several times a day. We can't survive more than a few days without water and we certainly can't put our bodies on hold until the environment is more suitable for us. Survival is tough for warm blooded animals.


How do hibernating warm-blooded animals (bears, squirrels etc) and cold blooded animals, such as crocodiles that have long periods of inactivity, maintain muscle mass and bone density? Human muscle wastes if not used. Why is this apparently not the case in many animals?


I have a question about a pet iguana. Since it is cold blooded and nights are cool, if I were drape a blanket over it, it wouldn't do any good because it cannot make its own body heat?


@anon6918 - Cold blooded animals use sunlight and natural heat to warm their bodies. While it's hard to tell whether they actually have warm or cold blood inside of their bodies, most people go off the assumption that it's warm blood in their veins.

This can easily be redirected to the fact that blood is an internal happening and while cold-blooded animals use natural heat to regulate their body temperature, even in cold situations their blood will remain warm because it's inside of the body. I'm not sure if there is a scientific explanation for it yet.


If warm blooded animals use:

Glucose + Oxygen -> Carbon Dioxide + Water (energy as heat)

to be warm-blooded, is there a reason cold blooded animals aren't cold blooded?

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    • Chameleon.
    • An alligator.
      An alligator.
    • Snakes are cold blooded.
      By: fivespots
      Snakes are cold blooded.
    • Like all amphibians, salamanders are cold blooded animals.
      By: Eric Isselée
      Like all amphibians, salamanders are cold blooded animals.
    • Cold blooded animals tend to thrive in remote locations like small islands.
      By: tanyapuntti
      Cold blooded animals tend to thrive in remote locations like small islands.