Estivation is essentially hibernation during periods of excessive heat or prolonged drought. An adaptation to environmental stress, this physiologic response is especially common in desert regions and in geographic areas that are characterized by dry seasons.
Land snails, terrestrial crustaceans and a wide variety of amphibians and reptiles are known to estivate. More than a retreat to cool or moist dens, this process involves a down-regulation of the animal's metabolism to preserve stored energy until environmental conditions improve. Many amphibians and invertebrates also secrete a membrane that protects them from dehydration through the estivation.
While many mammals den up during periods of excessive heat or drought, only a few species are known to estivate. Humans, of course, adapt to seasonal change with our various technologies but some of us (myself included), not being fans of hot weather, would love to estivate now and then.