poikilothermit

Poikilothermy is a biological term describing an organism whose body temperature varies considerably with the ambient environmental temperature. These organisms are often referred to as "cold-blooded," though this is a misnomer as their blood is not necessarily cold, but rather its temperature fluctuates. The internal temperature of a poikilotherm is largely determined by external factors such as sunlight, air temperature, and water temperature. This contrasts with homeotherms, which maintain a relatively stable internal body temperature regardless of external conditions.

Many poikilothermic animals, including reptiles, amphibians, fish, and insects, have evolved various behavioral and physiological mechanisms to cope with fluctuating temperatures. Behavioral thermoregulation is common, where animals move to warmer or cooler environments to achieve a desired body temperature. For example, a lizard might bask in the sun to warm up or retreat to the shade to cool down. Physiological adaptations can include changes in metabolic rate or the ability to tolerate a wider range of internal temperatures. Poikilothermy can be advantageous in environments where maintaining a constant high body temperature would require excessive energy expenditure, but it can also limit an organism's activity to certain temperature ranges.