What Is a Cold-blooded Animal?
Many animals, such as fish, frogs, snakes and lizards, are often called “cold-blooded,” as opposed to “warm-blooded” animals. This does not mean their blood is always cold. Unlike warm-blooded animals, they do not have built-in temperature controls that keep their bodies evenly warmed.
Instead, their body temperature is usually close to that of the surrounding air or water. Many cold-blooded animals depend on the sun for their body heat. Lizards, for example, bask in the sun to warm their bodies. All animals, except mammals and birds, are coldblooded.
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.
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.
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 bacteria cannot develop in cold environments efficiently.