Soaking Up the Sun

Imagine taking a nature hike along a creek. It’s a sunny spring morning. The sun feels warm, but the air is chilly.

A large gray rock sticks out of a muddy bank. A flash of color catches your eye. You step closer and see a lizard lying on the rock. Its skin shimmers in the sun. It is as still as a statue. Is it sleeping? No! The little lizard is sunbathing.

Lizards, snakes, and other reptiles are ectotherms. Fish, insects, worms, and frogs are ectotherms, too. Ectotherms produce very little heat inside their body. To warm up, they get heat from their environment.

The desert lizard basks in the sun to warm itself up. 

Energy from the sun helps this desert lizard dart and dash. 

That’s why the lizard is sunbathing. Sunlight strikes its body, warming it. The rock absorbs heat, too. This warms the lizard’s underside.

At night, the lizard’s body becomes as cool as the air around it. The low body temperature makes its muscles slow down. It will need the morning sun to warm up again.

Heat From the Inside

As you hike, you hear a sound: Clickety, clickety, clickety. It’s the sound of tiny claws on tree bark. Two squirrels chase each other around a tree trunk.

Unlike the lizard, these furry rodents don’t need sunlight for energy. That’s because squirrels and other mammals are endotherms. An endotherm is an animal that produces enough heat to keep its insides warm.

Squirrels don’t have to wait for the sun. They can be active the moment they wake up. So can birds. They are endotherms, too. And so can you.

That’s right! You are an endotherm. It doesn’t matter if it’s hot or cold outside. The inside of your body stays at the same warm temperature.

What’s In a Name?

Ectotherm and endotherm may sound like strange words. Yet, they make sense when you break them down.

Ectotherm comes from the Greek words ektos,meaning “outside,” and thermos, meaning “warm.” An ectotherm gets warmth from outside its body.

Endotherm comes from the Greek word endo, meaning “within.” An endotherm gets warmth from inside its body.