Wood frog © Joe Crowley
The wood frog (Lithobates sylvaticus) may be reddish, tan or dark brown but always has a dark mask under and behind the eyes. Some individuals have a light line down the middle of the back. This species has a dark blotch on the chest near each front leg. The belly is white and may have some dark mottling. Adult wood frogs can grow to up to eight centimetres in length. The call of this species is a series of sharp quacks, almost like those of a duck. Listen to the call of wood frog (courtesy of Adopt-A-Pond Wetland Conservation Programme).
No other frog in Ontario has a dark mask like the wood frog’s.
Although found on the tundra in the north and occasionally in grasslands in the west, the wood frog is most commonly associated with moist woodlands and vernal woodland pools. When inactive, this frog hides in logs, humus and leaf litter or under logs and rocks. It hibernates under logs or leaf litter on the forest floor.
View an interactive map of the known ranges of wood frogs in Ontario
Wood frogs have an astonishing ability to tolerate freezing. They can survive the freezing of 60 to 70 percent of the water in their body and sustained temperatures of -6°C. Consequently, wood frogs are the earliest breeders in most of their range, often beginning to call in early spring when ice is still on the ponds they frequent. This species is known to travel several hundred metres between breeding ponds and non-breeding terrestrial habitat. The female lays up to 2,000 eggs in a mass that is attached to submerged vegetation in small, fishless ponds. Females will change breeding ponds, if necessary, to avoid those that contain predatory fish. Wood frogs are explosive breeders: in a population, the females lay most of the egg masses within a few days. The males are so anxious to breed they will grab on to almost anything, including a human finger, as if trying to mate a female. When a female arrives in the wetland, it is common for many males to try to mate with her simultaneously, forming what naturalists call a “mating ball,” which can contain more than 15 frogs! The egg masses are clustered together so that their combined dark coloration warms them and speeds hatching. The tadpoles transform after 44 to 85 days. Adult wood frogs become sexually mature in two to three years.
These frogs can also change colour rapidly from very dark to very light. This is not so much an adaptive attempt at camouflage as it is a means of controlling body temperature: wood frogs darken when cold in order to absorb more heat. Adults of this species eat various small, mostly terrestrial invertebrates.
Other names: Rana sylvatica
Threats and Trends
This species is not at risk overall. The main threat to local populations is intensive timber harvesting practices that destroy or alter habitat by reducing canopy closure, understory vegetation, loose forest litter or dead wood in areas surrounding breeding sites. Negative impacts of such harvesting methods also extend at least 25 to 35 metres into uncut forest. Wood frogs are absent from most urban areas. Acidification, ozone depletion, predation or disease may also cause declines in wood frog populations. Despite these threats, wood frogs are generally widespread and abundant.
Current Status and Protection
Neither the Committee on the Status of Species at Risk in Ontario nor the Committee on the Status of Endangered Wildlife in Canada has assessed the status of the wood frog. The species has no protection under the Ontario Fish and Wildlife Conservation Act. The International Union for Conservation of Nature lists the global status of the wood frog as Least Concern. The species’ status was confirmed in 2010.
Learn more about reptile and amphibian conservation and what you can do to help these species on our Reptile and Amphibian Stewardship page.