Are Lizards Warm Blooded or Cold Blooded?

With a few exceptions all reptiles such as the lizard are cold blooded creatures.  The temperature of an animal’s blood (whether an animal is warm blooded or cold blooded) is related to its body temperature.

Cold blooded creatures such as the lizard take on the temperature of their surroundings.  In other words, they are hot when their environment is hot and cold when their environment is cold.  In hot environments, cold blooded animals can have blood that is much warmer than warm blooded animals.  Cold blooded animals are also much more active in warm environments and are very sluggish in cold environments.  This is because their muscle activity depends on chemical reactions which run quickly when it is and slowly when it is cold.  Cold blooded creatures such as the lizard can covert much more of its food into body mass compared to warm blooded animals.

Whereas many warm blooded animals sweat or pant to lose heat by water evaporation and can cool off by moving into a shaded area or getting wet, cold blooded animals such as the lizard often like to bask in the sun to warm up and increase their metabolism.  While basking, these reptiles will be found lying perpendicular to the direction of the sun to maximize the amount of sunlight that falls onto their skin.  In addition to this they will expand their rib cage to increase their surface area and will darken their skin to absorb even more heat.

When a lizard is too hot it will like parallel to the sun’s rays, go into a shady area, open its mouth up wide and lighten its skin color or burrow into the cool sand.  Most reptiles such as the lizard have been known to hibernate occasionally during the cold winter months.  Whereas warm blooded animals are able to remain active, seek food and defend themselves in a wide range of outdoor temperatures, cold blooded animals such as the lizard lack this ability and are only able to do so when they are warm enough.  A cold blooded animal’s level of activity depends upon the temperature of its surroundings.  A lizard will increase its body temperature before hunting and it is better able to escape from predators when it is warm.  These creatures also need to be warm and active in order to find a mate and reproduce.

Do not be fooled however, being cold blooded does have its advantages as well.  For instance, cold blooded animals require much less energy to survive than warm blooded animals do.  Mammals and birds (warm blooded creatures) require much more food and energy than do cold blooded animals of the same weight.  This is because in warm blooded animals, heat loss from their bodies is proportional to the surface area of their bodies, while the heat created by their bodies is proportional to the surface area of their bodies, the heat created by their bodies is proportional to their mass.

Furthermore, the ratio of a body’s surface area to its mass is less the larger the anima is.  What this means is that larger, warm blooded animals are able to generate more heat than they lose and more easily able to keep their body temperatures stable.  This in turn also makes it easier form them to stay warmer by being larger.  This also means that if a warm blooded animal is toop small it will lose its heat faster than it can produce it.  Since cold blooded animals don’t need to burn as much food to maintain a constant body temperature, they are more energy efficient and can survive longer periods of time without food than warm blooded creatures can.  Many cold blooded creatures will try to keep their body temperatures as low as possible when food is scarce.

Cold blooded creatures also have the advantage of being less prone to infections than warm blooded animals.  This lies in the fact that being a warm blooded body provides a warm environment for viruses, bacteria and parasites to reside.  As a general rule, mammals and birds since they are warm blooded, are usually prone to more problems with infections and such than reptiles, whose constantly changing body temperature make life more difficult for bacteria, etc. to survive in.

Mammals do however; still have a stronger immune system than cold blooded animals.  A reptile’s immune system is more efficient when the animal is warmer, however since bacteria are known to most likely grow slower in lower temperatures, reptiles will sometimes lower their body temperatures when they have an infection.


  1. angela says

    Hi, i was at the reptile part of the zoo and was very interested in the knowledge written about the lizards. was it written that they are not cold blooded??? can you please verify as i believed they were cold blooded.

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