Animal
Wood frog
The wood frog is a small brown frog with a dark mask around its eyes. It lives in forests from Alaska to the eastern United States. In winter, much of its body freezes, and in spring it thaws out and hops away!
The wood frog is a brown forest frog with a dark "robber's mask" across its eyes. It lives farther north than any other North American amphibian, reaching Alaska and northern Canada. To survive winter it lets much of its body freeze, protected by sugar in its cells, and in early spring it is one of the first frogs to call, with a sound like quacking ducks.
Lithobates sylvaticus is a freeze-tolerant ranid frog whose range reaches farther north than that of any other North American amphibian. Glucose acting as a cryoprotectant lets it survive months frozen in the leaf litter. It breeds explosively in fish-free ponds in early spring and is abundant, stable and Least Concern.
Photo: The Cosmonaut, CC BY-SA 2.5 CA, via Wikimedia Commons
Meet the wood frog
The wood frog is a small brown frog.
It has a dark patch like a mask across its eyes and a white line on its lip. It lives in cool forests and freezes in winter!
The wood frog is a small frog, about 3.5 to 7.6 centimeters long, and females are much bigger than males. Most are brown, tan or rusty, but some are greenish or gray. All of them have a dark patch that runs from the eye back over the eardrum, like a robber's mask, and a white line along the upper lip.
Wood frogs live in forests across Canada, Alaska and the eastern United States. They are famous for something amazing: they survive winter partly frozen.
Lithobates sylvaticus (often still called Rana sylvatica) is a true frog of the family Ranidae. Adults measure 3.5 to 7.6 centimeters, females much larger than males (Animal Diversity Web). Color morphs range from brown, tan and rust to green and gray, but all share a dark mask extending over the tympanum to the base of the forelimb, a white upper-lip stripe and usually a light dorsolateral fold.
The IUCN states that its range reaches farther north than that of any other North American amphibian. Its tolerance of freezing has been studied in detail in Interior Alaska.
Quick facts
- Group
- Amphibian
- Length
- 3.5 to 7.6 cm
- Lifespan in the wild
- 3 to 5 years
Where it lives
Wood frogs live in Canada and the United States.
They live in forests and near ponds. In winter they hide under leaves and logs on the forest floor.
Wood frogs live from Alaska across Canada to Labrador, and south to New Jersey, northern Georgia and northern Idaho, with scattered groups in the Rocky Mountains and in Arkansas and Missouri. They live farther north than any other amphibian in North America.
They live in many kinds of woodland, at the edges of ponds and streams and in willow thickets. When they are resting, they hide in logs, leaf litter and soft forest soil. In spring they lay their eggs in small ponds that have no fish.
The IUCN range runs from Alaska to Labrador and south to New Jersey, northern Georgia and northern Idaho, with a patchy distribution south to northern Colorado in the Rocky Mountains and disjunct subpopulations in Arkansas and Missouri. It occurs in every Canadian province and territory listed, from Newfoundland to Yukon and Nunavut.
Habitats include many forest and woodland types, pond and stream edges, willow thickets and grass-willow-aspen associations. Inactive frogs shelter in logs, humus and leaf litter. Breeding takes place mostly in small, fish-free ponds, temporary or permanent, usually in woods; experiments suggest adults can detect predatory fish and avoid those ponds.
Continent
Its habitats
Where can you find this animal?
- Lives here naturally · Countries and seas named by a scientific source
- Sightings recorded · Records of wild sightings (GBIF)
Lives here naturally · Countries and seas named by a scientific source
Forests, woodland ponds, stream edges and willow thickets from Alaska across Canada to Labrador, south to New Jersey, northern Georgia and northern Idaho, with scattered groups in the Rocky Mountains to northern Colorado and in Arkansas and Missouri. It does not live in the southern and western United States.
Places: Canada and United States.
Source: iucn-red-list · checked October 2026
Sightings recorded · Records of wild sightings (GBIF)
Counts of GBIF records of wild observations (human and machine) and preserved specimens. Records include introduced populations, vagrants, escaped or released animals and misidentifications, so a country with records is not necessarily part of the native range.
Wild sightings have been recorded in United States, Canada, Germany and Namibia.
Source: gbif · checked October 2026
Range maps show where scientists say an animal lives, often country by country. An animal may live in only part of a country shown, and sightings records can include animals that wandered far from home.
What it eats
Wood frogs eat bugs and other small animals.
Their tadpoles eat tiny green plants called algae and bits of old leaves.
Grown-up wood frogs eat many kinds of insects and other small invertebrates that live on the forest floor. They are active in the daytime and rely on their brown colors to blend in while they hunt.
Tadpoles eat differently. They graze on algae, nibble rotting plant and animal matter, and sometimes eat eggs. Wood frogs are food for many other animals too, from garter snakes and herons to raccoons and mink, so they are an important link in the forest food web.
Adults eat a variety of terrestrial insects and other small invertebrates, and larvae consume algae, decaying plant and animal matter and eggs (Animal Diversity Web). The species is diurnal and relies heavily on cryptic coloration on the forest floor.
As both predator and prey it links aquatic and terrestrial food webs: adults are eaten by larger frogs, garter, ribbon and water snakes, herons, raccoons, skunks and mink, while tadpoles fall prey to diving beetles, water bugs and salamander larvae. ADW notes that older tadpoles develop glands that repel many predators, and adults' skin secretions deter shrews.
Did you know?
Wood frog tadpoles know their brothers and sisters.
Wood frog tadpoles can recognize their brothers and sisters and gather together with them.
Wood frog larvae show some of the strongest kin recognition known in amphibian larvae, aggregating with siblings in natural ponds (ADW).
A frog that freezes
In winter, ice forms in much of a wood frog's body.
Sugar inside its body keeps it safe. In spring it thaws out and hops away!
Wood frogs spend winter just under the leaves and soil of the forest floor, where it freezes. They let much of their body turn to ice: scientists have measured from about a third to more than half of the body frozen.
Their trick is sugar. As the frog starts to freeze, it fills its cells with glucose, a kind of sugar, which stops the cells from drying out and being damaged. In Alaska, scientists found wood frogs that stayed frozen for more than six months, at temperatures as low as minus 18 degrees Celsius, and all of them survived.
Wood frogs overwinter in shallow hibernacula under leaf litter and duff, and tolerate the formation of ice in their bodies; a 2014 press release on research presented to the Society for Integrative and Comparative Biology described Alaskan frogs freezing upward of 60 percent of their bodies (Animal Diversity Web gives 35 to 45 percent). Glucose acts as a cryoprotectant: concentrating sugar inside cells balances the salts that build up outside as ice forms, so less water is drawn out and the cells do not desiccate (University of Alaska Fairbanks researchers, via ScienceDaily).
Larson and colleagues tracked frogs in Interior Alaska: they stayed below freezing for 193 plus or minus 11 days, with minimum temperatures of minus 8.9 to minus 18.1 degrees Celsius, and all 18 survived. Ten to fifteen freeze-thaw cycles in early October raised tissue glucose far above lab-frozen frogs (13 times higher in muscle, 10 times in heart). Earlier studies of frogs from the eastern United States and Canada had found survival only for a few weeks and to about minus 7 degrees Celsius.
From egg to frog
In early spring, wood frogs lay big clumps of eggs in ponds.
Tadpoles hatch and swim. They grow legs, lose their tails and hop out of the pond as tiny frogs.
As soon as the first warm spring rains arrive, wood frogs wake up and hurry to their ponds, often before all the ice has melted. Each female lays a round clump of 1,000 to 3,000 eggs. After about a week the clump flattens and floats, and tiny green algae living in the jelly turn it green.
The eggs hatch after 9 to 30 days, depending on how warm the water is. The olive-brown tadpoles grow for about two to four months. Then comes metamorphosis: the back legs appear first, then the front legs, lungs replace the gills, and the tail is slowly absorbed. The new froglets, only 16 to 18 millimeters long, leave the pond. Males can breed after one or two years, females after two or three.
Wood frogs are explosive breeders: in late winter or early spring, with the first warm rains, adults migrate to breeding ponds, showing strong site fidelity (in one Shenandoah study, all breeding adults returned to the pond where they first bred, while about 18 percent of juveniles dispersed to new ponds; IUCN). Each female lays a globular mass of 1,000 to 3,000 eggs, 10 to 13 centimeters across, which later flattens at the surface and turns green with symbiotic algae (ADW).
Hatching takes 9 to 30 days depending on water temperature. Tadpoles metamorphose at 50 to 60 millimeters, 65 to 130 days after hatching, into juveniles of 16 to 18 millimeters; as in other frogs, hind limbs appear before forelimbs, lungs replace gills and the tail is resorbed as an energy source (Australian Museum). Males mature one to two years after metamorphosis and females two to three. Wood frog tadpoles show unusually strong kin recognition, gathering with their siblings.
First to sing in spring
Wood frogs sing very early in spring.
Their song sounds like ducks quacking. After the eggs are laid, they go quiet again.
Wood frogs are among the very first frogs to call each year, sometimes while ice still covers part of the pond. A chorus of males sounds like a flock of quacking ducks or chuckling. Once breeding is over, after only a short time, they fall silent for the rest of the year.
The rest of the year, wood frogs live quietly on their own in the forest. If a predator grabs one, it may give a loud, piercing cry that can startle the attacker into letting go.
Males call almost exclusively during the short breeding season, producing duck-like quacking choruses, and fall silent afterward (ADW). Because males cannot tell the sexes apart by sight, they clasp any frog they meet; a clasped male gives a release croak, and females that have already spawned are released because they are thin.
Outside the breeding season wood frogs are largely solitary and diurnal. Their main defense is cryptic coloration; if seized, they may emit a piercing distress cry that can make a predator let go.
Did you know?
Wood frog eggs turn green.
Tiny green algae grow in the jelly around wood frog eggs, turning the whole clump green.
Egg masses flatten at the surface after about a week and turn green from symbiotic algae living in the jelly (ADW).
Abundant, but needs ponds and forests
There are lots and lots of wood frogs.
They need forests and small ponds without fish. Keeping those places safe helps wood frogs.
Wood frogs are abundant and widespread, and their numbers are stable, so they are listed as least concern. No big threat endangers the species as a whole.
Locally, though, wood frogs can be harmed when forests around their breeding ponds are heavily logged, because they need shade, fallen logs and leaf litter. Small spring ponds, sometimes called vernal pools, are easy to drain or fill in, so protecting them helps wood frogs and many other animals.
The IUCN assessed the wood frog in 2020 (published 2022) as Least Concern: abundant, widespread and stable, with no known significant threats to the global population and no record of use or trade.
Local threats come from intensive timber harvesting that reduces canopy closure, understory, loose forest litter and decaying woody debris around breeding sites, with negative effects reaching at least 25 to 35 meters into uncut forest. In northern Minnesota, successful breeding in acidic bog water is rare or absent. Animal Diversity Web describes wood frogs, like other amphibians, as useful indicators of environmental health.
IUCN Red List
How is the wood frog doing in the wild?
- Least Concern (this animal)
- Near Threatened
- Vulnerable
- Endangered
- Critically Endangered
- Extinct in the Wild
- Extinct
Least Concern
Not at risk of disappearing from the wild right now.
See the IUCN Red List assessment · The IUCN Red List of Threatened Species 2022.2
Listen to wood frogs
Listen to the recording at the start of this page.
That is a group of wood frogs calling in spring. Does it sound like ducks to you?
At the start of this page you can play a real recording of wood frogs, made on March 2, 2023 in West Windsor, New Jersey. That early date shows how soon in spring wood frogs begin to call.
Listen for the low, clucking, quacking sounds. Each one is a male wood frog calling at a breeding pond. Many people mistake a wood frog chorus for ducks.
The recording on this page was made by Ryan Hodnett in West Windsor, New Jersey, on March 2, 2023, early in the breeding season. Wood frog calls are short, low, clucking notes often compared to quacking ducks or chuckling (ADW), repeated several times in a row. Calls are given almost only during the brief spring breeding period, so a chorus like this is a sure sign that wood frogs have arrived at their ponds.
Did you know?
Wood frogs can stay frozen for months and still wake up in spring.
In Alaska, wood frogs stayed frozen for more than six months, at down to minus 18 degrees Celsius, and all of them survived.
Alaskan wood frogs tracked in the wild stayed below freezing for 193 plus or minus 11 days with minima to minus 18.1 degrees Celsius and 100 percent survival (Larson and colleagues, SICB 2014).
Amazing facts
-
Wood frogs can stay frozen for months and still wake up in spring.
In Alaska, wood frogs stayed frozen for more than six months, at down to minus 18 degrees Celsius, and all of them survived.
Alaskan wood frogs tracked in the wild stayed below freezing for 193 plus or minus 11 days with minima to minus 18.1 degrees Celsius and 100 percent survival (Larson and colleagues, SICB 2014).
-
Wood frog eggs turn green.
Tiny green algae grow in the jelly around wood frog eggs, turning the whole clump green.
Egg masses flatten at the surface after about a week and turn green from symbiotic algae living in the jelly (ADW).
-
Wood frogs sound like quacking ducks.
A chorus of wood frogs sounds so much like ducks that people often think a flock is on the pond.
The male advertisement call is a short, low cluck repeated several times, widely compared to a duck's quack (ADW).
-
Wood frog tadpoles know their brothers and sisters.
Wood frog tadpoles can recognize their brothers and sisters and gather together with them.
Wood frog larvae show some of the strongest kin recognition known in amphibian larvae, aggregating with siblings in natural ponds (ADW).
Words to know
- freeze-tolerant
- able to survive ice forming inside the body
- glucose
- a kind of sugar that living things use for energy
- metamorphosis
- a big change in body shape as an animal grows, like a tadpole becoming a frog
- tadpole
- the young, water-living stage of a frog
- vernal pool
- a small pond that fills in spring and may dry up in summer
- eardrum
- the round, thin skin a frog hears with, just behind its eye
Discovery challenge
-
What happens to a wood frog in winter?
How does a wood frog get through winter?
Which strategy lets wood frogs survive winter in the leaf litter?
- It flies south
- Much of its body freezes, and it thaws in spring
- It swims in warm water all winter
Show the answer
Much of its body freezes, and it thaws in spring
Much of its body freezes. In spring it thaws out and hops away!
It lets much of its body freeze, and sugar in its cells protects it until spring.
Freeze tolerance: glucose acts as a cryoprotectant while ice forms outside the cells.
-
What does a wood frog's song sound like?
What does a chorus of wood frogs sound like?
How is the wood frog's breeding call usually described?
- A roaring lion
- Quacking ducks
- A ringing bell
Show the answer
Quacking ducks
It sounds like ducks going quack, quack!
A wood frog chorus sounds like a flock of quacking ducks or chuckling.
Short, low, clucking notes, widely compared to a duck's quack.
-
What protects a freezing wood frog?
What does a wood frog fill its cells with as it freezes?
Which cryoprotectant accumulates in wood frog tissues during freezing?
- Sugar (glucose)
- Salt
- Mud
Show the answer
Sugar (glucose)
Sugar inside its body keeps it safe while it is frozen.
Glucose, a kind of sugar, stops the cells from drying out and being damaged.
Glucose; in Alaskan frogs, freeze-thaw cycles raised muscle glucose 13-fold over lab-frozen frogs.
-
Where do wood frogs lay their eggs?
What kind of pond do wood frogs choose for their eggs?
What breeding sites do wood frogs prefer?
- In the ocean
- In small ponds without fish
- In tree holes
Show the answer
In small ponds without fish
They lay eggs in small ponds that have no fish.
Small ponds in the woods with no fish, so fewer eggs and tadpoles get eaten.
Small, fish-free ponds, temporary or permanent; adults can detect predatory fish and avoid those ponds.
Places where you might see it
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Watch
Country
Canada
Canada is the second-largest country in the world, stretching across the north of North America from the Atlantic to the Pacific and up into the Arctic. It has the Rocky Mountains, thousands of islands and about 42 million people, who speak English, French and many other languages.
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Watch
Country
United States
The United States is a large country in North America made of 50 states, from icy Alaska to the warm islands of Hawaii. It has the Grand Canyon, the Mississippi River and Yellowstone, and about 342 million people live there.
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Common frog
The common frog is a familiar frog of ponds and gardens across Europe. It spends most of the year in damp grass, gardens and woods, and every spring it returns to ponds to lay clumps of frogspawn that grow into tadpoles and then little froglets.
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Canada is the second-largest country in the world, stretching across the north of North America from the Atlantic to the Pacific and up into the Arctic. It has the Rocky Mountains, thousands of islands and about 42 million people, who speak English, French and many other languages.
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American bullfrog
The American bullfrog is the largest true frog in North America. It lives in warm, still ponds and lakes, sits and waits for food to come close, and the males' deep 'jug-o-rum' call carries more than a kilometer. Its tadpoles can take years to turn into frogs.
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Amazon milk frog
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For parents & teachers
What children will learn
- Explain how wood frogs survive winter by tolerating freezing, and what glucose does.
- Describe the wood frog life cycle and metamorphosis from egg mass to froglet.
- Recognize a wood frog by its mask and its duck-like spring call.
- Understand why small fish-free ponds and nearby forests matter for frogs.
Recommended ages: 3 to 17 · About 15 minutes
Talk about it
- Why might a frog that lives in the far north benefit from freezing instead of digging deep underground?
- Why would a frog choose a pond with no fish, even if it dries up in summer?
- What could your community do to protect small spring ponds?
Try at home or in class
- Freeze two small cups of water, one plain and one with lots of sugar dissolved in it, and compare how hard and icy each becomes.
- Play the recording on this page and try to imitate the wood frog's quacking call, then listen outdoors on a warm, rainy early-spring evening with an adult.
Key vocabulary: freeze-tolerant, glucose, metamorphosis, tadpole, vernal pool, eardrum
Where these facts come from
- The IUCN Red List of Threatened Species , International Union for Conservation of Nature (IUCN terms of use (no redistribution of Red List data or range maps))
- GBIF Backbone Taxonomy and GBIF Occurrence Search , Global Biodiversity Information Facility (CC0 1.0 (backbone); occurrence counts are facts derived from records under CC0, CC BY and CC BY-NC)
- Wikimedia Commons , Wikimedia Foundation (Per file: Public domain, CC0, CC BY or CC BY-SA only (credited on each page))
- Lithobates sylvaticus (Wood Frog), IUCN Red List assessment 2022 , IUCN
- Lithobates sylvaticus (Wood Frog) , Animal Diversity Web, University of Michigan Museum of Zoology
- Wood frog adaptations to overwintering in Alaska: new limits to freezing tolerance (Larson, Middle and Barnes, abstract) , Society for Integrative and Comparative Biology
- Frozen frogs: How amphibians survive the harsh Alaskan winters , Newswise (Society for Integrative and Comparative Biology)
- Alaska wood frogs spend most of their life frozen (University of Alaska Fairbanks release) , ScienceDaily
- Frog life cycle, from egg to adult , Australian Museum
- Wikidata , Wikimedia Foundation (CC0 1.0)
Checked, not yet human-reviewed. Last updated October 27, 2026. Spotted a mistake? Tell us.