Temperature Regulation
Snakes are typically ectothermic creatures. Cold-blooded is a hoary misnomer: so-called cold-blooded animals actually have warm blood.
Endothermic animals have internal mechanisms to self-regulate internal body temperature, at the expense of a greater metabolism: requiring roughly double the energy for every 10 °C rise in temperature.
Ectothermic animals need an external assist to regulate their body temperature: typically, sunlight or something warmed by sunlight. Snakes, like all ectotherms, keep warm by behavioral habits.
The long, slender snake body has a high surface-to-weight ratio. Since heat is absorbed over a surface, snakes can increase heat uptake by stretching out. Flattening out is even better, both for catching rays from above and warming the underside by conduction.
Snakes must keep themselves between 4–38 °C or risk death. Their body temperatures are typically higher than their surroundings: around 30 °C (versus 23 °C room temperature).
While active, many snakes can maintain their body temperatures within a desired 1 °C range. This is remarkable considering snakes lack feathers, fur, or other insulation, and skin is far from ideal for retaining heat.
Heat can be conserved by coiling. Snakes, even those of different species, will sometimes aggregate to keep warm and conserve moisture.
When prevailing conditions make it impossible to adequately regulate themselves, snakes retreat to dormancy. Adders in northern Europe hibernate 8 months of the year. Conversely, tropic regions, with long, dry, hot summers force snakes to sequester themselves in a cool burrow or beneath the bark of a tree to avoid dehydration.
Water snakes are limited in thermoregulatory opportunities. Hence, aquatic marine snakes are found only in the warm-water regions of the world.
