Wood frogs are a northern species that can survive temperatures below freezing. They do not typically hibernate in the water, instead they usually over winter in top soil or under brush piles. They survive freezing temperatures by storing up urea in their tissues prior to the on slot of winter. Their liver also begins to convert glycogen into large quantities of glucose as the temperatures begin to fall. The urea and glucose act as a kind of antifreeze allowing the frog to survive the winter as long as over 65% of their body water does not freeze.