Frogs: Skin Breathing, Freezing & Survival

A frog is, in a real sense, two animals living one life. It starts as a gilled, fully aquatic larva and ends as an air-breathing adult that can climb trees, burrow underground, or in a few cases survive being frozen solid through a Northern winter. That transformation, metamorphosis, is only the beginning of what makes frogs biologically strange: many species breathe partly through their skin, some derive lethal poisons entirely from what they eat rather than producing it themselves, and as a group they're currently at the center of one of the largest disease-driven extinction events ever documented in a vertebrate group.

With roughly 8,000 recognized species, frogs make up the vast majority of living amphibians, and understanding a handful of their shared adaptations explains why they show up almost everywhere from rainforest canopies to the Arctic Circle, and why so many of them are now disappearing.

Quick Facts About Frogs

Fact	Information
Common name	Frog (includes toads, which are not a separate formal taxonomic group)
Scientific classification	Order Anura, class Amphibia
Number of species	About 8,000 recognized species (AmphibiaWeb, September 2026), making up roughly 88% of all living amphibians
Size	From under 1 cm (some Paedophryne species) to about 32 cm body length (Goliath frog)
Diet	Mostly carnivorous as adults — insects, other invertebrates, and, in larger species, small vertebrates; tadpoles are often herbivorous or omnivorous
Habitat	Freshwater wetlands, rainforests, grasslands, deserts, mountains, and even the Arctic tree line
Geographic range	Every continent except Antarctica
Lifespan	Commonly 2–10 years in the wild for most species, though some can live considerably longer
Activity pattern	Mostly nocturnal or crepuscular, though many species are active by day
Conservation status	Highly variable by species — from Least Concern to Extinct in the Wild
Population trend	Overall declining as a group, driven largely by habitat loss and disease

What Actually Separates a Frog From a Toad?

"Frog" and "toad" aren't separate scientific categories. All toads are frogs, biologically speaking; "toad" is a common name usually applied to species with drier, warty, glandular skin and shorter hind legs suited to walking or hopping short distances, versus the smoother, moister skin and long, powerful legs of frogs built for leaping. Every species in the order Anura shares a tailless adult body plan (the name Anura literally means "without a tail"), a shortened, fused vertebral column called a urostyle that stiffens the body during jumps, and elongated ankle bones that function as an extra lever segment in the hind legs, extending jump distance well beyond what the leg length alone would suggest. That leg architecture is a large part of why frogs are such disproportionately powerful jumpers relative to body size, and why the same basic skeletal blueprint shows up whether the species in question spends its life in a treetop, a desert burrow, or a pond.

How Frogs Breathe Through Their Skin

Adult frogs have lungs, but lungs are only part of the story. Frog skin is thin, richly supplied with blood vessels close to the surface, and kept constantly moist by mucus glands, which together let oxygen and carbon dioxide diffuse directly across it a process called cutaneous respiration. This is why frog skin has to stay damp to function properly, and why so many species are tied to humid microhabitats even when they're not actively swimming. 

Cutaneous respiration becomes especially important during long underwater periods, including winter dormancy, when a frog submerged in cold, oxygen-containing water can meet much of its basic metabolic needs through its skin alone, without ever surfacing to use its lungs. It's a trade-off rather than a superpower: skin gas exchange is far less efficient than lung ventilation, particularly in warm or oxygen-poor water, which is why frogs still rely on lungs during activity and only lean heavily on skin breathing when their metabolic demands are low, such as during hibernation.

Why Some Frogs Can Freeze Solid and Survive

The North American wood frog takes winter survival further than almost any other vertebrate: it allows up to 65–70% of the water in its body to freeze solid, with breathing, heartbeat, and detectable brain activity all stopping for months at a time. What keeps this from being fatal, the way it would be for most animals, is a rapid biochemical response triggered the moment ice begins forming. The wood frog's liver dumps large amounts of glucose into the bloodstream, and this glucose acts as a cryoprotectant, limiting how much ice forms inside individual cells and reducing the cell shrinkage and membrane damage that freezing would otherwise cause. Research on Alaskan wood frog populations near the northern edge of the species' range has found even more extreme tolerance, with some individuals surviving core body temperatures well below what southern populations can withstand, tied to larger glycogen reserves and greater cryoprotectant production. Once temperatures rise in spring, the frog thaws from the inside out and resumes normal function within hours, with no lasting organ damage from an event that would kill nearly any mammal.

The Diet-Toxicity Secret Behind Poison Dart Frogs

Poison dart frogs don't manufacture their own poison. Research led by scientists including those at the Smithsonian's National Zoo has confirmed what's known as the diet-toxicity hypothesis: these frogs sequester alkaloid toxins directly from the ants, mites, and beetles they eat in the wild, storing the compounds unchanged in skin glands rather than synthesizing anything themselves. This explains a phenomenon well documented in captivity poison dart frogs raised on a "clean" diet of crickets and fruit flies, which don't carry the relevant alkaloids, grow up essentially non-toxic, no matter how brightly colored their warning patterns remain.

Conservationists working on reintroduction programs have specifically studied whether adding alkaloid-rich prey back into captive frogs' diets can restore toxicity before release, since a poison frog without poison loses the chemical defense its bright coloration evolved to advertise in the first place. The vivid colors themselves are a separate, related adaptation called aposematism warning coloration that lets a genuinely toxic frog be active in the open during the day, since most predators quickly learn to avoid anything that bright.

From Gilled Larva to Air-Breathing Adult: Why Metamorphosis Matters

Frog metamorphosis is a more complete transformation than the term "growing up" suggests. A tadpole hatches with external or internal gills, a long finned tail for swimming, and mouthparts typically built for scraping algae or filtering organic material, functioning essentially as a different animal from what it will become. Triggered by thyroid hormone, metamorphosis dismantles gill structures, grows lungs and limbs, reshapes the digestive tract from a long herbivore-style gut to a shorter one suited to a mostly carnivorous adult diet, and eventually resorbs the tail entirely. This life-history split matters ecologically as much as biologically: it lets frogs exploit two very different food webs across a single lifespan, grazing algae and detritus as aquatic larvae before switching to hunting insects and other invertebrates as terrestrial or semi-aquatic adults, and it's also the reason frog populations are vulnerable to problems at two entirely separate habitat stages a polluted pond can wipe out a generation of tadpoles even if the surrounding terrestrial habitat is intact for adults.

Calling and Reproduction

Male frogs of most species attract mates with calls amplified by one or more vocal sacs, elastic pouches of skin that inflate with air pushed back and forth from the lungs, acting as a resonating chamber that projects sound far beyond what the vocal cords alone could produce. Calls are typically species-specific, letting females identify and locate a suitable mate even in a chorus made up of several overlapping species at once. Fertilization in the large majority of frog species is external: a male grips a female from behind in a mating clasp called amplexus, and as she releases eggs into water he releases sperm over them simultaneously. 

Clutch sizes and strategies vary enormously by species, from a handful of eggs guarded closely by a parent to thousands of eggs released with no further care, and a smaller number of species have evolved direct development, skipping the free-swimming tadpole stage entirely and hatching as miniature versions of the adult.

Conservation: The Chytrid Fungus Crisis

Frog conservation status has to be read against a specific, well-documented catastrophe: the amphibian chytrid fungus, Batrachochytrium dendrobatidis, which infects and disrupts the very skin function frogs depend on for both respiration and water balance. A comprehensive global assessment published in Science in 2019 found the fungus has caused documented population declines in at least 501 amphibian species, roughly one in every 16 known to science at the time, and has driven at least 90 species to extinction or presumed extinction in the wild, with another 124 species declining by more than 90%. The fungus spreads through water and direct contact, has been detected on every continent where amphibians live, and appears to have originated in Asia before spreading globally, likely aided by the international pet and food trade. Beyond chytrid, individual frog species face the more familiar threats of wetland habitat loss and fragmentation, pollution and agricultural runoff affecting sensitive breeding ponds, and, for a smaller number of species, overcollection for the pet trade or traditional medicine. Conservation status therefore varies enormously by species rather than following a single global trend: many widespread frogs remain Least Concern, while numerous range-restricted species, particularly mountain-stream specialists in Latin America and Australia, are Critically Endangered or already gone. Responses include captive assurance colonies for the most at-risk species, habitat protection for remaining wetlands, and ongoing research into probiotic skin treatments and selective breeding for chytrid resistance.

Ecological Importance

Because frogs sit in the middle of the food web, both as predator and prey, and because they cycle between aquatic and terrestrial habitats across their lifetimes, they function as an unusually efficient link moving energy and nutrients between water and land. Tadpoles graze algae and process organic matter in ponds and streams, while adult frogs consume large numbers of insects, helping to regulate populations of mosquitoes and crop pests in the habitats they occupy.

In turn, frogs and their larvae are a major food source for fish, birds, snakes, and mammals, meaning a local decline in frog numbers can ripple outward to species that depend on them. Their permeable skin also makes frogs unusually sensitive to water and air pollution, which is why researchers frequently use frog population health as a bioindicator a practical early-warning signal for broader environmental degradation that might not yet be visible in less sensitive species.

Fascinating Facts About Frogs

Frog skin absorbs water directly rather than drinking it. Most frogs don't drink through the mouth at all; instead, they absorb water through a specialized patch of skin on the belly and thighs, sometimes called a "drinking patch," while sitting in damp soil or shallow water.

Some species skip the tadpole stage entirely. In direct-developing frogs, mostly found in tropical regions, eggs hatch directly into fully formed miniature frogs, with the tadpole stage occurring entirely inside the egg.

A frog's eyes help it swallow. Frogs retract their large eyeballs downward into the roof of the mouth when swallowing, using the pressure to help push food down the throat — a behavior visible as a distinct blink each time a frog eats.

The Goliath frog is large enough to eat small vertebrates. As the largest living frog species, it has been documented preying on other frogs, small fish, and even small birds or bats, in addition to the insects that make up most frog diets.

Captive breeding can strip a species of its most famous trait. As described above, poison dart frogs raised without access to their natural alkaloid-bearing prey grow up largely non-toxic, showing that the poison is entirely diet-derived rather than an inherent trait of the animal itself.

Frog calls can be identified almost like fingerprints. Because calls are species-specific and often frequency-distinct even among closely related species calling in the same pond, researchers use acoustic monitoring, sometimes with automated recorders, to survey frog populations without needing to physically capture individuals.

Some frogs change color with temperature or mood, not just for camouflage. A number of species show measurable color shifts tied to temperature, humidity, or stress, a physiological response distinct from the more familiar background-matching camouflage seen in many amphibians.

Frequently Asked Questions

Are toads a different species from frogs?
No. "Toad" is a common name, not a formal taxonomic rank, generally applied to frogs with drier, warty skin and shorter legs adapted for walking rather than leaping. Every toad is scientifically classified within the order Anura, the same order that includes every other frog.

Can frogs really breathe entirely through their skin?
Not entirely, but substantially. Cutaneous respiration supplements lung breathing and becomes especially important during extended submersion, such as winter dormancy, when a frog's oxygen demand is low enough that skin gas exchange alone can sustain it for long periods.

Is it true that a frog can be frozen and still survive?
Yes, in certain species. The wood frog is the best-documented example, tolerating the freezing of most of its body water for months at a time through a glucose-based cryoprotectant system, then thawing and resuming normal activity in spring with no lasting organ damage.

Why are so many frog species declining if habitat loss isn't the main issue everywhere?
The chytrid fungus is a major additional driver independent of habitat quality — it has caused documented declines even in protected, pristine habitat, because it spreads through water and direct contact and specifically disrupts the skin function frogs rely on, something habitat protection alone can't prevent.

Are all brightly colored frogs poisonous?
No, and the reverse assumption can be dangerous when applied backward, since some non-toxic frogs mimic the bright warning colors of genuinely toxic species without producing or sequestering any toxin themselves. Toxicity in true poison frogs specifically comes from a diet of particular alkaloid-bearing arthropods, not from color alone.

How can I tell if frog populations in my area are healthy?
Because frogs are sensitive to water quality and often the first species to disappear from degraded habitat, consistent presence and calling activity during breeding season is generally a reasonable sign of local wetland health, while sudden silence in a historically active breeding pond is often an early indicator worth investigating.

Sources & Further Reading

• AmphibiaWeb — Amphibian Species by the Numbers
• National Geographic — "Amphibian 'apocalypse' caused by most destructive pathogen ever" (reporting on Scheele et al., Science, 2019)
• Smithsonian's National Zoo and Conservation Biology Institute — "After An Insect Detox, Can Once-Poisonous Frogs Get Their Spice Back?"
• PeerJ — Gerber, Wijenayake & Storey, "Anti-apoptotic response during anoxia and recovery in a freeze-tolerant wood frog" (Carleton University)
• Wildlife Conservation Society — "The Frog That Can Freeze"
• AccessScience (McGraw Hill) — "Anura" overview
• Georgia Aquarium — Wood Frog species profile