Difference between Cold-Blooded and Warm-Blooded Animals

In biology, animals are divided into two major groups according to thermoregulation inside their organisms: cold-blooded and warm-blooded. In the following article, we will explore the differences between the two groups.


Cold-Blooded vs Warm-Blooded Animals
A thermographic image of a snake around an arm with a temperature scale on the right

Cold-blooded animals, also referred to in biology as ectothermic, or poikilothermic animals, cannot keep their internal temperature at the level necessary for their survival. Their bodies are not able to regulate their temperature. When it’s cold outside, their bodies also get cold. This is the reason why they need to get to the sun in order to receive a sufficient amount of heat radiation in order to survive the following night, when it’s cold. If you have ever seen a snake lying on a stone perpendicular to the direction of the sun, that was the reason. Some fish species that inhabit cold water regions move into the deeper depths of the water environment during the winter season; it is warmer there. Some fish also develop proteins in their blood that help them battle freezing. Some insect species simply die when it’s cold, yet some of them can move, like birds, to warmer regions where they can survive the following winter. Bees have the unique ability to produce heat with wing movements; they also keep together in order to get warm.

Cold-blooded animals are much more active when it’s warmer than when it’s cold. This is due to the chemical reactions in their muscles that go much faster when it’s warm.

Types of cold-blooded animals:

  • Reptiles
  • Amphibians
  • Insects
  • Arachnids

Mammals (including human beings) and birds are the two main categories of warm-blooded animals.

Warm-blooded animal
An Arctic hare, a warm-blooded animal which is able to survive severe cold

Warm-blooded animals, also known as endotherms, or homoeothermic animals, use the energy they receive with food to stay warm. Mitochondria, the doubled-membrane organelles that are present in most cells of warm-blooded animals, are responsible for producing energy. Generally, warm-blooded animals sustain the same amount of energy all their lives, no matter what the temperature of the outside environment is. However, with extreme temperatures outside, the body of the warm-blooded animal can change a little bit.

When the body of a warm-blooded animal is overheated, it releases excessive heat via the process of sweating, which is made possible by sweat glands situated under their skin. Primates have these glands all over their bodies, while dogs and cats have them only at their feet. The other way to not be overheated is to be in a water environment. Whales do not need sweat glands for the reason that they live in water. For the same reason elephants have very large ears – they sweat through them; for large animals it can be difficult to get rid of excessive heat in the body. The reverse task – not to be overcooled – is achieved via means of fur (which these animals shed before summer season), shivering, and, in the case of some of birds, migration to warmer regions before winter starts.

Because of the dependence on the external conditions, warm-blooded animals are slower at nights and during the early morning hours, when it is colder outside.

Cold-blooded animals vs Warm-blooded animals

What is the difference between cold-blooded animals and warm-blooded animals?

  • Cold-blooded animals do not use food to create heat. Warm-blooded animals’ bodies, on the other hand, transform the energy absorbed with the food into heat. This is the reason why cold-blooded animals do not need to eat as much food as warm-blooded animals do.
  • Cold-blooded animals’ sleep phases are described in biology as hibernation (winter sleep in warm places which may last the whole duration of winter) and aestivation (summer sleep; the animal sleeps in cold or at least shady places). Warm-blooded animals, on the other hand, do not have such phases. There are few exceptions to the latter, though. The Californian pocket mouse and bats of all kinds do hibernate; the latter are not categorized by some biologists as either cold-blooded or warm-blooded animals.

    All reptilia are cold-blooded animals
  • Warm-blooded animals are equally active in both cold and warm environments. Thanks to that, they are able to find food anywhere. This ability allows them to survive in any place on the planet. Cold-blooded animals, on the other hand, have to be sufficiently warm in order to be active at all. For this reason, they cannot live, for example, in high mountain regions – their bodies have to receive heat from the outside. They are also only able to mate and to reproduce when it’s warm enough.
  • For warm-blooded animals, the bigger the surface of the body, the more heat they need to lose in order to remain in heat equilibrium; and, the bigger the mass of such animal, the larger amount of heat they generate. Together that means, the larger a warm-blooded animal, the easier for it to maintain its temperature. For cold-blooded animals, on the other hand, the ratio of the weight/ surface of a body/ generated heat is inapplicable. Because of all that, warm-blooded animals cannot be as small as some of cold-blooded animals, like, for example, some species of lizards and fish.
  • Warm-blooded animals attract a lot of foreign malignant microorganisms precisely because of their stable internal temperature. Bacteria and various kinds of parasitic worms feel at home in their bodies. Cold-blooded animals, on the other hand, do not provide such a welcoming environment for foreign microorganisms, and, because of that, they get sick much less compared to warm-blooded animals. For that reason, the latter species developed a much stronger and more sophisticated immune system. Most reptiles get cooler, should they be invaded by bacteria, because bactriacannot develop in cold environments efficiently.

Comparison chart

Cold-blooded animals Warm-blooded animals
Reptiles, amphibians, insects, arachnids Mammals, birds
Do not use food to create heat Use food to create heat
Do not need much food; require less energy to survive Need food all the time; require more energy to survive
The temperature of the body depends on the temperature of the environment The temperature of the body doesn’t depend on the temperature of the environment
Are characterized by winter sleep and summer sleep stages Winter sleep and summer sleep phases are not characteristic for these animals
Can survive only in sufficiently warm environments Can survive in any environment, including extremely cold
Microorganisms like viruses can hardly survive in their bodies Are easier targets for foreign microorganisms, like viruses
The immune system is weaker The immune system is stronger


In this video you can see an analysis that explains the basic differences between cold-blooded animals and warm-blooded animals: