Cold-blooded animals are animals whose body temperature changes with the temperature of their environment instead of staying constant. They are also called ectotherms or poikilotherms and include most fish, amphibians, reptiles, and invertebrates such as insects and spiders.

What cold-blooded means

Cold-blooded animals do not generate enough internal heat to keep a stable body temperature, so they rely on external heat sources like sunlight, warm surfaces, or warm water. When it is cold, their metabolism slows, they move less, and many can survive long periods without eating because their energy needs are low.

Main groups and examples

Major cold-blooded groups include:

• Reptiles: snakes, lizards, turtles, tortoises, alligators, and crocodiles.

• Amphibians: frogs, toads, salamanders, and newts.

• Fish and most sharks, plus many other aquatic species.

• Invertebrates: insects, arachnids (like spiders), crustaceans (crabs, lobsters, shrimp), and many others.

How they stay warm or cool

To control temperature, cold-blooded animals change behavior instead of burning energy like mammals and birds do. Common strategies include basking in the sun, moving into shade or water, burrowing underground, changing depth in water, or entering torpor/hibernation during cold seasons.

Advantages and limits

Because they do not spend much energy making body heat, cold-blooded animals often survive on little food and can handle harsh or food-poor environments. However, they are usually active only within certain temperature ranges and can become sluggish, “cold stunned,” or even die if conditions get too cold or change too quickly.

Cold- vs warm-blooded at a glance

Feature| Cold-blooded animals| Warm-blooded animals
---|---|---
Body temperature| Changes with environment.46| Kept nearly constant.46
Main groups| Fish, amphibians, reptiles, most invertebrates.135| Mammals and birds.46
Energy use| Low; can go long without food.14| High; need frequent food.14
Activity in cold| Slow or inactive; may hibernate/torpor.35| Often still active due to internal heat.46