FaunaHub

Wood Frog (Lithobates sylvaticus)

AmphibianFrogNorth America

Wood frog (Lithobates sylvaticus), a brown frog with a dark robber's-mask eye stripe.

Wood frog (Lithobates sylvaticus).

Image: Jasper Shide, CC0, via Wikimedia Commons.

Overview

The wood frog (Lithobates sylvaticus) is a small to medium brown frog of North America, easily known by the dark “robber's mask” patch through each eye. What makes it truly extraordinary is its cold-hardiness: the wood frog has one of the widest ranges of any North American amphibian, reaching far into the north — it is one of the very few frogs found above the Arctic Circle — and it survives the brutal winters by performing a near-miracle of biology.

Each winter the wood frog literally freezes: up to roughly two-thirds of the water in its body turns to ice, its heart stops, and it lies frozen and motionless — then, in spring, it thaws and comes back to life, hopping off to breed as if nothing had happened.

Note: details here cover the wood frog as a species; treat general statements as approximate and verify against authoritative sources.

Habitat & Range

Wood frogs live across a huge swath of North America, from the southern Appalachians up through Canada and Alaska and into the Arctic — the most northerly range of any frog on the continent. True to their name, they spend much of the year in moist woodland and forest floor, and they breed in temporary woodland pools, ponds, and other fish-free waters in early spring.

Diet

Wood frogs are insectivores, eating a variety of small invertebrates — insects, spiders, worms, slugs, snails, and other tiny creatures — caught among the leaf litter and vegetation of the forest floor. Their tadpoles graze on algae and organic matter in the breeding pools before transforming into froglets.

Behavior

The wood frog's claim to fame is freeze tolerance. As temperatures drop, it floods its tissues with natural “antifreeze” compounds — especially glucose, drawn from its liver — that protect its cells while ice forms in the spaces around them. In this frozen state the frog has no heartbeat, no breathing, and no measurable brain activity, yet when it warms in spring it thaws from the inside out and resumes normal life. Wood frogs are also famous “explosive breeders”: very early in spring, often while ice still rims the ponds, large numbers gather at breeding pools for just a few days, the males giving a quacking, duck-like chorus, before dispersing back into the woods. Outside breeding they are terrestrial and rather secretive.

Human Interaction & Conservation

Wood frogs are harmless and widespread, and they are of great interest to scientists, whose studies of the frog's freeze tolerance and natural antifreeze inform research into preserving cells, tissues, and organs. They depend on clean woodland breeding pools and intact forest, so habitat loss, the draining of vernal pools, pollution, and disease are the main concerns, though the species remains common across much of its vast range. Consult AmphibiaWeb and the IUCN Red List for current status.

More photos of the wood frog

A wood frog on leaf litter, showing its dark eye mask.

Wood frog (Lithobates sylvaticus).

Image: Ryan Hodnett, CC BY-SA 4.0, via Wikimedia Commons.

Frequently Asked Questions — Wood Frog

Can a wood frog really freeze solid and survive?
Remarkably, yes — though 'frozen solid' is a slight exaggeration. In winter a large fraction of the water in a wood frog's body (up to around two-thirds) turns to ice, its heart stops, and it stops breathing, appearing lifeless. Natural antifreeze compounds protect its cells, and when it warms in spring the frog thaws and revives, hopping off to breed. Few vertebrates can endure anything like it.
How does the wood frog avoid dying when it freezes?
By managing where the ice forms and protecting its cells. As it cools, the frog floods its tissues with 'cryoprotectant' compounds — especially glucose released from the liver — that keep ice from forming inside its cells and limit damage, while ice forms in the spaces around them. This controlled freezing lets the frog survive being frozen for weeks at a time.
Why is the wood frog important to science?
Because of its freeze tolerance. Researchers study how the wood frog protects its cells and organs while frozen — and revives unharmed — for insights that could help with preserving human cells, tissues, and transplant organs at low temperatures. A humble frog has become a model for the science of surviving the cold.
Where do wood frogs live, and why do they breed so early?
They range across northern North America — including above the Arctic Circle, the most northerly of any frog there — living in moist woodland and breeding in temporary pools. They're 'explosive breeders' that gather at thawing ponds very early in spring, sometimes amid lingering ice, breeding in just a few days. Using short-lived, fish-free pools helps their eggs and tadpoles avoid predators.

Sources and further reading

Authoritative wildlife references used for general educational context. Conservation status should always be verified against current IUCN Red List data. External links open in a new tab.