The wood frog, Lithobates sylvaticus, is an amphibian found across North America. It exhibits remarkable adaptations, thriving in diverse environments from southern forests to the Arctic Circle. Its life cycle involves distinct habitat uses throughout the year, showcasing its flexibility and resilience.
Their North American Range
The wood frog’s contiguous range extends from northern Georgia and the southern Appalachian Mountains, northward through eastern Canada, and westward into Alaska and southern British Columbia. This makes it the most widely distributed frog in Alaska and the most northerly amphibian in the Western Hemisphere, found even above the Arctic Circle. Across this vast territory, the wood frog primarily inhabits boreal and temperate forests, though it can also be found in tundra and certain grasslands.
Life in Forest and Upland Environments
Wood frogs spend most of their active lives in terrestrial environments, particularly moist woodlands, forests, and swamps. These non-breeding habitats provide essential resources for their survival, including moisture, camouflage, and abundant invertebrate prey. They typically reside on the forest floor, seeking refuge under logs, rocks, and within damp leaf litter. This preference for shaded, humid conditions helps them retain moisture, avoid desiccation, and forage for insects, spiders, worms, and slugs.
The Importance of Vernal Pools
Vernal pools are the exclusive breeding habitat for wood frogs. These temporary woodland ponds fill with water from snowmelt and spring rains, typically drying by summer. Their ephemeral nature means they are generally devoid of fish, which would otherwise prey on wood frog eggs and tadpoles. In early spring, often while snow still covers the ground, adult wood frogs emerge from hibernation and migrate to these pools for an “explosive” breeding period lasting one to two weeks. Females deposit large, gelatinous egg masses, sometimes communally, attached to submerged vegetation, ensuring rapid offspring development before the pools evaporate.
Surviving Winter Underground
During colder months, wood frogs hibernate terrestrially, often in shallow burrows or under leaf litter and loose soil on the forest floor. Unlike many other frog species that overwinter underwater, wood frogs remain near the surface, typically just above the frost line. They can tolerate the freezing of up to 65-70% of their body water. Their bodies produce high concentrations of glucose and urea, acting as cryoprotectants that prevent ice crystals from forming inside cells and protect tissues from damage. While frozen, their heart, breathing, and blood circulation cease, yet they can thaw and resume normal activity in spring, often emerging early to breed.