Ectotherms vs. endotherms

Do you know the difference between an ectotherm and an endotherm—or even what these terms mean? They both refer to the ways that animals stay warm. When the weather outside is frightful, a blog post about thermoregulation is so delightful! Keep reading to find out which animals need help from the environment to stay warm (ectotherms), and which animals produce their own heat (endotherms).


For these animals, heat comes from outside (ecto-) their bodies—their environment provides their warmth. That means they require less food, and are consequently able to inhabit places that would be off-limits to endotherms. However, their activity level is limited by the surrounding conditions. If it gets too cold, they simply can’t move.

Banggai cardinalfish (Pterapogon kauderni)

Like most fish, Banggai cardinalfish are ectotherms. Because of this, these fish appear less hungry during winter months.

Banggai cardinalfish


Widehand hermit crabs (Elassochirus tenuimanus)

Hermit crabs, along with all invertebrates, are ectotherms. Since invertebrates account for more than 95 percent of animal species, that means that most animals are ectotherms

Widehand hermit crab


Tripod fish (Family Ipnopidae)

These fish live in the abyssal zone, where conditions are so stable that their body temperatures don’t change.

Tripod fish



These animals produce their own heat inside (endo-) their bodies. Creating that warmth speeds up their body processes: muscles, neurons and all of their processes work faster. That also means they require a lot of food—between five and 20 times more food than an ectotherm of the same size!

Sea otters (Enhydra lutris)

These marine mammals have to eat roughly 25 percent of their body weight per day to keep their bodies warm.

Sea otter


Anna’s hummingbirds (Calypte anna)

These high-energy birds have needs that can’t be met at night when they’re at rest. The solution? Torpor, a state of deep sleep and lowered metabolism. Some animals extend torpor over the whole winter; this is called hibernation.

Anna’s hummingbird


Opahs (Lampris guttatus)

These fish generate heat mainly by constantly flapping their pectoral fins, which helps their bodies stay warmer than the water even when they dive over 1,500 feet below the surface. Opahs have been sighted in Washington waters twice since 1935.



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