An ectotherm is an animal that must use environmental energy and behavioral adaptations to regulate its body temperature. Non-bird reptiles, such as the Python regius (“ball python”) snake curled up in the corner of the picture shown, absorb external heat instead of generating much of their own. Some ectotherms sometimes have inadequate sources of internal heat, while others have none. Ectotherms do not require as much food as endotherms of the same size. However, many cannot deal as well with cold surroundings. Ectotherms are sometimes referred to as “cold-blooded animals”, a term which is not very accurate or appropriate. The ectotherms include many fishes, reptiles, amphibians, and invertebrates.