These hibernacula are not as well protected from frigid weather and may freeze, along with their inhabitants. And yet the frogs do not die. True enough, ice crystals form in such places as the body cavity and bladder and under the skin, but a high concentration of glucose in the frog's vital organs prevents freezing. A partially frozen frog will stop breathing, and its heart will stop beating. It will appear quite dead.
Estivation is similar to hibernation.
It is a dormant state an animal assumes in response to adverse environmental conditions, in this case, the prolonged dry season of certain tropical regions. Several species of frog are known to estivate. When the dry season starts, these frogs burrow into the soil and become dormant. These herpetological mummies remain in their cocoons for the duration of the dry season. When the rains return, the frogs free themselves of their shrouds and make their way up through the moist soil to the surface.