See the Difference

Have you ever held a lizard? How about snake or a turtle? In each of these cases, an endotherm (you) touches an ectotherm. The ectotherm’s body temperature is likely lower than yours. You couldn’t tell that just by looking at the animal, and you probably wouldn’t be able to feel a difference, either. But the difference is stark when you look at thermal infrared images. These images show how cool or warm an object is by measuring the amount of heat it gives off.





By fanning its ears, this elephant begins to cool down.

This spider’s body is cooler than its environment.

Look at the thermal image above
of someone holding a lizard.
As the scale shows, the brighter the color, the warmer the temperature. The bright red of the hand shows that the person maintains a warm, steady body temperature, even though the surrounding air is cooler.

The lizard shows up mostly as shades of blue. Before being held, it appeared as dark blue or black, just like the background. No surprise there—the lizard’s body temperature was the same as the temperature of the surrounding air.

But what happens as the reptile and mammal touch? The reptile absorbs heat from the person’s hand. The lizard’s tail still appears dark blue because it isn’t being touched. The rest of the lizard’s body is warming noticeably, with its feet and legs showing up as green and yellow. How do you think the lizard would appear if the person continued to hold it?

This cat generates its ownbody heat.
It leaves behind a trail of warm pawprints.

Watch as a person leaves
warm footprints on a cold floor.






As this gharial soaks up the sun’s rays, its body temperature begins to rise.

Food also provides energy. The body uses that energy to move. Energy from food also produces heat. In this way, an animal’s body is like a furnace, except instead of burning natural gas or oil, the body “burns” food.

The faster an animal’s metabolism, the
more energy the animal has for keeping warm and moving around.
Which kind of animal— ectotherm or endotherm—do you think has the faster metabolism?

A Living Furnace

Why can some animals maintain a constant internal temperature while others cannot? The answer comes down to one word— metabolism.

An animal’s metabolism is all of the chemical reactions that take place in the animal’s body, and in your body, too. Tiny molecules are constantly combining and breaking apart in body cells, forming new substances. Most of these chemical reactions in the body occur as food breaks down.

You need food to stay alive. So does every other living thing. Food provides the materials to grow and to repair damaged cells. For instance, if you cut your finger, new cells grow out from either side of the cut and heal it. The materials for those new cells come from the food you eat.




These meerkats don’t need to wait for the sun; they regulate their own body heat and are already warm.




Some of these flamingos have one leg that is hotter than the other. When a flamingo stands on one leg, that leg loses heat, while the other leg is tucked up next to its body keeping warm.

You guessed it—endotherms. The metabolism of birds and mammals, including humans, is fast enough to generate constant warmth, allowing the animals to maintain a high body temperature. Birds have the fastest metabolism and the highest body temperature, 40o C to 42o C (104o F to 108F). Can you think of a reason birds would need such a fast metabolism? Think about how birds move. The high rate of metabolism produces the energy birds need to fly.

On the other hand, an ectotherm’s metabolism is slow. It can’t generate enough heat to warm the animal’s body. An ectotherm’s metabolism depends on the temperature of the environment. When the air warms up, an ectotherm’s metabolism increases.