Other names: Rana sylvatica, Northern Wood Frog
The Wood Frog is a medium-sized frog reaching up to 8 cm in body length. They range from reddish, tan, or dark brown with a white upper lip stripe and a dark mask that stops abruptly behind the . Wood Frogs have a dark blotch on the chest near each front leg, and some may have a light line down the back. The belly is white and may have some dark mottling. Wood Frogs also have prominent and their toes are not fully webbed. During the breeding season, males will have a swollen thumbpad and two throat pouches that will inflate as they call. Wood Frog tadpoles are dark gray to dark brown all over with a faint, light stripe along the upper jaw and a light-coloured belly. Tadpoles can reach up to 6.5 cm in length before metamorphosis.
Wood Frog Call
The Wood Frog call consists of a burst of short ‘quacks’, sounding like a small duck.
The Wood Frog is the most widespread amphibian in Canada, found in every province and territory. It exists in Nunavut only in the southernmost tip of the territory and is absent in Newfoundland but is found in Labrador. In British Columbia, Wood Frogs are widespread in the central and northern Interior, and along the Rocky Mountains and East Kootenays where they may be found at elevations up to 3050 m. Contrary to most frogs in North America, the Wood Frogs’ distribution is mostly in Canada. In the United States, Wood Frogs are found throughout the northeast and there are small, isolated population in Colorado, Wyoming, and northern Idaho.
Wood Frogs generally hibernate in soil, using root channels and old burrows, and are active from March through to October, with more northern populations having shorter active seasons. Wood Frogs are one of the first amphibians to begin calling and breeding in the spring, and are often active when there is still snow on the ground. Wood Frogs are largely terrestrial but are usually found close to water. They prefer moist woodlands and vernal pools associated with deciduous and boreal forests, but is also found in tundra and occasionally in grassland habitats. Wood Frogs breed in shallow, temporary wetlands that are free of fish, typically in forested areas. They have been observed breeding in ditches, road ruts, ponds, and shallow bays in lakes. Tadpoles are generally found in the warmest, shallowest parts of wetlands.
Wood Frogs are the earliest breeders in almost all of their range. The breeding season is explosive, and will be completed after one or two weeks in April or May, depending on latitude. Fertilization happens externally in aquatic habitats as the male grasps the female in. The female will lay up to 2,000 eggs in a mass 4-10 cm in diameter. Eggs are typically laid in very shallow water, or are attached to vegetation within 15 cm of the water surface. Eggs are black on top and white underneath. Egg development is rapid, with hatching occurring within 1-3 weeks depending on the water temperature. Tadpoles will metamorphose after 6-12 weeks. Males reach maturity after 1-2 years, which is quicker than females after 2-3 years. Time to sexual maturity may be longer in northern populations with restricted active seasons. Wood Frogs generally do not live to be older than 5 years.
Wood Frogs are experts at hunting invertebrates and prefer insects, worms, snails, mollusks and other invertebrates, usually the terrestrial forms. Tadpoles are herbivorous and feed on algae and aquatic plants.
In Canada, Wood Frogs are very widespread and abundant. Much of their range is expansive through undeveloped areas of northern Canada. The threats to Wood Frogs throughout their range appear to be minimal. The primary threat to Wood Frogs is the loss of forest habitat and breeding wetlands. Roads can cause high levels of mortality where roadways intersect migration paths to and from breeding areas. Pollution from pesticides and herbicides, road salt, and sediment from forestry can cause mortality and developmental defects. Chytrid fungus has been found in Wood Frogs in British Columbia, but deaths have not been recorded. Climate change is a threat to all frog species as it may increase the frequency and severity of drought and flood events.
Did You Know?
Wood Frogs are freeze tolerant and generally hibernate under logs or leaf litter on the forest floor. They produce a natural ‘antifreeze’ by increasing the amount of glucose in the blood which prevents ice particles from forming within their cells. Wood Frogs can change colour very quickly to go from very dark, to very light. When it is cold, they will darken themselves to absorb more heat.
Adult Wood Frogs can actually tell if a potential breeding site may contain predatory fish by “smelling” the water!
When attacked by a predator, adult and transforming Wood Frogs secrete a repulsive substance from their skin as a deterrent.