Ectothermic Animals

Why Reptiles Aren't Actually Cold-Blooded

Hawksbill Turtle (Eretmochelys imbricata) swimming above coral reef, underwater view
Paul Souders/Digital Vision/Getty Images

An ectothermic animal, also commonly known as a "cold-blooded" animal, is one who cannot regulate its own body temperature, so its body temperature fluctuates according to its surroundings. The term ectotherm comes from the Greek ektos, meaning outside, and thermos, which means heat. 

While common colloquially, the term "cold-blooded" is misleading because ectotherms blood isn't actually cold. Rather, ectotherms rely on external or "outside" sources to regulate their body heat.

 Examples of ectotherms include reptiles, amphibians, crabs, and fish.

Ectothermic Heating and Cooling

Many ectotherms live in environments where very little regulation is needed, like the ocean, because the ambient temperature tends to stay the same. When necessary, crabs and other ocean-dwelling ectotherms will migrate toward preferred temperatures. Ectotherms who live mainly on land will use basking in the sun or cooling off in the shade to regulate their temperature. Some insects use the vibration of the muscles that control their wings to warm themselves without actually flapping their wings. 

Due to ectotherms dependence on environmental conditions, many are sluggish during the night and in early in the morning. Many ectotherms need to heat up before they can become active. 

Ectotherms in the Winter

During the winter months or when food is scarce, many ectotherms enter torpor, a state where their metabolism slows or stops.

Torpor is basically a short-term hibernation, which might last from a few hours to overnight. The metabolic rate for torpid animals can decrease up to 95 percent of its resting rate. 

Ectotherms can also hibernate, which can occur for a season and for some species like the burrowing frog, for years.

The metabolic rate for hibernating ectotherms falls to between one and two percent of the animals resting rate.Tropical lizards have not adapted to cold weather so they do not hibernate. 

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Kennedy, Jennifer. "Ectothermic Animals." ThoughtCo, Aug. 29, 2017, Kennedy, Jennifer. (2017, August 29). Ectothermic Animals. Retrieved from Kennedy, Jennifer. "Ectothermic Animals." ThoughtCo. (accessed March 21, 2018).