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Animal lists · 12 entries

Cold-Blooded Animals

Ectothermic animals — including reptiles, amphibians, most fish and all insects — rely on external heat sources to regulate body temperature, unlike endothermic mammals and birds which generate heat internally; "cold-blooded" is informal and ectothermic is the precise term.

Updated 25 July 2026

Cold-blooded is informal language for ectothermy — relying on external heat to set body temperature. Warm-blooded means endothermy — generating heat internally. The distinction is not absolute: tuna and some sharks elevate muscle temperature above ambient, and naked mole rats behave more like ectotherms than typical mammals.

This list covers the major ectothermic groups with notes on exceptions and on why ectothermy is a successful strategy rather than a deficiency.

How this list was compiled

Entries are major animal groups that are primarily ectothermic — body temperature determined primarily by external environment rather than internal heat production. Endothermic exceptions within groups (tuna, brooding pythons) are noted. The term poikilothermy (variable body temperature) is distinguished from ectothermy (heat source external). Mammals and birds are excluded as endotherms.

Cold-Blooded Animals

  1. Lizard

    Ectothermic; basks for heat

    Must bask to raise body temperature before activity. Retreats to shade when too hot.

  2. Snake

    Ectothermic; behavioural thermoregulation

    Moves between sun and shade to maintain preferred body temperature. Some pythons shiver to incubate eggs — partial endothermy.

  3. Crocodile

    Ectothermic; aquatic basking

    Basks with mouth open — possibly for thermoregulation through evaporative cooling from the mouth lining.

  4. Turtle

    Ectothermic; nest temperature determines sex

    Body temperature follows environment. Nest temperature during incubation determines sex in most species.

  5. Frog

    Ectothermic; moist skin

    Skin must stay moist for respiration and temperature regulation. Activity ceases in cold weather.

  6. Salamander

    Ectothermic; aquatic and terrestrial

    Most species are fully ectothermic. Some high-altitude species tolerate near-freezing body temperatures.

  7. Fish (most species)

    Ectothermic; exceptions in tuna and sharks

    Most fish match water temperature. Tuna and great white sharks retain muscle heat above ambient — regional endothermy.

  8. Insects (all species)

    Ectothermic; rapid temperature change

    Small size means body temperature equilibrates quickly with surroundings. Bumblebees shiver to warm flight muscles.

  9. Spider

    Ectothermic

    Activity levels depend on ambient temperature. Many species become dormant in cold weather.

  10. Crab

    Ectothermic; intertidal exposure

    Intertidal crabs tolerate wide temperature swings between submerged and exposed periods.

  11. Shark (most species)

    Mostly ectothermic; regional endothermy in some

    Great white, mako and porbeagle sharks retain muscle heat above water temperature — regional endothermy, not full endothermy.

  12. Naked mole rat (exception)

    Mammal that behaves as ectotherm

    Poor thermoregulation for a mammal — body temperature follows burrow temperature. Included as the exception that proves the rule.

Key facts

  • Ectothermic animals rely on external heat — basking, sheltering, moving between microhabitats — to set body temperature.
  • Cold-blooded is informal; ectothermic is the precise biological term. Warm-blooded means endothermic.
  • Ectothermy is not inferior — it requires far less food energy than endothermy, which is why reptiles can fast for months.
  • Some fish and sharks show regional endothermy — retaining muscle heat above ambient without full endothermy.
  • Insects are ectothermic but bumblebees shiver to warm flight muscles before take-off.
  • The naked mole rat is a mammal with poor thermoregulation — body temperature follows its burrow environment.

Cold-Blooded Animals: frequently asked questions

What are cold-blooded animals?
Ectothermic animals — reptiles, amphibians, most fish and all insects — whose body temperature is determined primarily by the external environment rather than internal heat production.
Are cold-blooded animals always cold?
No. A lizard basking in desert sun can have a body temperature higher than a mammal's. Cold-blooded means temperature varies with the environment, not that the animal is always cold.
What is the difference between cold-blooded and warm-blooded?
Cold-blooded (ectothermic) animals rely on external heat sources. Warm-blooded (endothermic) animals generate heat internally — mammals and birds. The distinction is about heat source, not temperature value.
Are sharks cold-blooded?
Most are ectothermic, matching water temperature. Great white, mako and porbeagle sharks retain muscle heat above ambient — a form of regional endothermy.
Why are reptiles cold-blooded?
Ectothermy requires far less food energy than endothermy. A crocodile can fast for months; a mammal of similar size cannot. The trade-off is dependence on external heat to become active.
Are any mammals cold-blooded?
Not truly, but the naked mole rat has poor thermoregulation and its body temperature follows burrow conditions — the closest mammalian approximation to ectothermy.

Sources

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