Temperature Regulation

Ectotherms are animals that warm their bodies by absorbing heat from their surroundings. In most ectotherms, the body temperature fluctuates with changes in the surrounding temperature. The body temperature of snakes, for example, cools in cold weather and warms up in hot weather. Most marine fish and invertebrates, however, live in water that stays the same temperature. Their body temperature, therefore, does not change. In everyday language, we say that these animals are cold-blooded. Amphibians, reptiles, most fish, and invertebrates are considered cold-blooded. This term is misleading, however, because many lizards have high body temperatures. External temperature plays a major role in the activity rate of ectothermic animals. When the weather is warm, they become active. They slow down when the temperature drops.

Certain ectotherm behaviors help regulate body temperature. To warm up, reptiles find sunny places, and stretch out for maximum exposure. If it gets too warm, lizards alternate between sun and shade. Amphibians warm up by moving into the sun or diving into warm water. They cool off by entering the shade. In cold weather, honeybees huddle together to retain heat. Bees and large moths build up heat before takeoff by contracting their flight muscles without moving their wings.

In addition to behaviors, physiological adaptations help ectotherms regulate temperature. Diving reptiles conserve heat because their blood circulates inward toward the body core during a dive. The skin of bullfrogs secretes more mucus when it is hot, allowing more cooling by evaporation. Many ectotherms exist at a lower temperature during torpor, a state of slowed metabolism. This helps them survive a food shortage. If the food supply increases, they come out of torpor in a few hours.