coldbloods

Cold-blooded is a common, informal term for animals that rely largely on external heat sources to regulate their body temperature. In biology, these animals are described as ectothermic. Major groups include reptiles (such as snakes, lizards, turtles, and crocodilians), amphibians (frogs and salamanders), fishes, and many invertebrates (including insects, mollusks, and crustaceans). The label is useful in everyday language but is imprecise; true endothermy, the ability to maintain a stable internal temperature through metabolic heat, is uncommon in these groups.

Body temperature in cold-blooded animals generally tracks the surrounding environment. Metabolic rate tends to rise with temperature, enabling greater activity in warmer conditions, but also increasing energy needs. In cooler conditions, activity and growth often slow. Many ectotherms use behavioral strategies to regulate heat, such as basking in the sun to warm up, seeking shade or burrowing to cool down, or becoming active at night when temperatures are milder. In aquatic species, water temperature strongly influences physiology due to its high heat conductivity and steady thermal properties.

Ecologically, cold-blooded animals inhabit a wide range of environments, from deserts to tropical forests and oceans. They exhibit diverse life histories and reproductive strategies; for example, some reptiles show temperature-dependent sex determination, and amphibians are often highly sensitive to environmental changes. Climate fluctuations and habitat loss can disproportionately affect ectotherms, whose body temperatures and activity are tightly tied to ambient conditions.

Terminology note: while widely used, the term "cold-blooded" is informal. Scientists prefer ectotherm or poikilotherm, reflecting the reliance on external heat sources rather than implying a universally cold physiology.