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Canadian Herpetological Society

Société d'herpétologie du Canada

Lithobates sylvaticus,

formerly Rana sylvatica

Wood Frog / Grenouille des bois

Wood Frog

This is a moderate sized, true frog with prominent dorsolateral ridges. It may be reddish, tan or dark brown with a dark mask that ends abruptly behind the tympanum. Some individuals have a light line down the middle of the back. There is a dark blotch on the chest near each front leg. The belly is white and there may be some dark mottling. The toes are not fully webbed. Adults may reach up to 8 cm.

The call is a series of sharp quacks, almost like a duck. The call of Cope's Gray Treefrog is similar but more musical and with more trill.

Confusing Species
In eastern Canada there are no other frogs with both a mask and dorsolateral ridges. In western Canada, Columbia Spotted Frogs, Oregon Spotted Frogs and Northern Red-legged Frogs can all have a dark mask but none have a white underside.

The Wood Frog is the most widely distributed amphibian in Canada and is found in every province and territory. It is also found in the eastern and north-central United States.

Although found in tundra to the north and occasionally in grasslands in the west, the Wood Frog is most commonly associated with moist woodlands and vernal woodland pools.

Wood Frogs are the earliest breeders in most of their range, often beginning to call when their is still ice on the ponds in spring. The egg mass of up to 2,000 eggs is attached to submerged vegetation. Most of the egg masses in a population will be laid within a few days and clustered together so their combined dark colouration warms them and speeds hatching. The tadpoles transform after 44-85 days.

Natural History
Wood Frogs are freeze tolerant and hibernate under logs or leaf litter on the forest floor. Wood Frogs can change colour rapidly from very dark to very light. They will darken when cold in order to absorb more heat.

Conservation Concerns
Wood Frogs are very widespread and abundant.