Life Cycle of a Frog

Short answer

• The familiar life cycle of a frog runs from egg to tadpole to froglet to adult frog, with metamorphosis as the transformation in the middle.
• Eggs usually hatch into aquatic tadpoles that breathe with gills, swim with a tail, and feed mainly on algae and other small organic material in the water.
• During metamorphosis, tadpoles grow legs, develop lungs, lose their gills, and absorb the tail into the body.
• A froglet looks like a small adult frog but still has part of its tail. Once the tail is gone, the young frog spends more time on land.
• Timing varies widely. Some tadpoles transform in weeks, while American bullfrog tadpoles can take up to two years.
• The textbook sequence is not universal. Some frogs skip the free swimming tadpole stage and hatch directly as tiny froglets.

The Life Cycle in One View

A frog begins life in a form that looks nothing like an adult frog, and it ends life in a form built for a different world. That is why the frog life cycle is such a useful example in biology. It is not just growth, in which an animal gets bigger while staying roughly the same shape. It is a rebuild, in which feeding, breathing, movement, and habitat all change.

For most familiar pond frogs, the sequence has five recognizable parts: egg, tadpole, tadpole with legs, froglet, and adult frog. Metamorphosis is not one of those parts on its own. It is the process that carries the animal from the tadpole form to the frog form, and it overlaps the leg growth and froglet stages. Some summaries count three stages, egg, larva, and adult, and some count four, egg, tadpole, froglet, and adult. Those counts are not in conflict. They are different ways of grouping the same changes, with more or less detail in the middle.

Stage	What defines it	Typical timing in familiar pond species
Egg	Embryo inside a jelly coat, usually in water	Days to a few weeks, depending on species and temperature
Tadpole	Aquatic larva with gills and a swimming tail, no legs at first	Weeks to months, sometimes longer
Tadpole with legs	Back legs appear first, then front legs, while the tail shortens	Weeks within the tadpole period
Froglet	Small frog shape with a short tail still present	Days to weeks at the end of metamorphosis
Adult frog	Tail gone, lungs working, life centered on land and the water edge	Months to years to reach breeding maturity, depending on species

Stage 1: Eggs and the Start of Life

Frog reproduction in the familiar sequence begins at water. Males of many species gather at ponds, lakes, marshes, or slow streams and call to attract females. The call is often species specific, which helps a female find a mate of her own species in a pond shared with other frogs. When a female is ready, the male clasps her in a hold called amplexus while she releases eggs, and he fertilizes them externally as they are laid. Fertilization outside the body is one reason so many eggs are needed. Not every egg will be fertilized, and not every fertilized egg will survive.

The eggs themselves are easy to recognize in many pond species. Each dark embryo sits inside a clear jelly coat, and the coats stick together in a mass or string. The jelly helps hold the eggs together, keeps them moist, and gives some protection, but it is not armor. Eggs are eaten by fish, insects, birds, and other aquatic animals, and they are sensitive to drying, sudden cold, pollution, and disturbance.

Egg number varies greatly by species. The American Museum of Natural History notes that female American bullfrogs can lay up to 20,000 eggs in long strings. That very large number is not typical of every frog, and it should not be quoted as a general frog figure. It does explain a basic pattern, though. Frogs that lay huge numbers of eggs usually give their young no parental care after laying. Survival depends on numbers, on hiding places among plants, and on luck, not on guarding.

Egg placement also varies. Many pond frogs attach egg masses to submerged plants, sticks, or rocks near the surface, where the water is warmer and oxygen is available. Some frogs lay eggs in other places entirely. The Smithsonian’s National Zoo describes lemur leaf frogs laying eggs on leaves or branches over water. The embryos develop in the egg, then wiggle out, drop into the water below, and continue as tadpoles. The starting point is different, but the later aquatic stage is still present in that species. True direct developers go further, and skip the tadpole stage altogether, as described later.

How long eggs take to hatch depends on species and on water temperature. Warmer water usually speeds development, while colder water slows it. In many familiar species, hatching takes days to a couple of weeks. That range is broad on purpose. A single number for all frogs would hide the very variation that makes the life cycle interesting, and it would be wrong for species at either end of the range. Inside the egg, the embryo changes from a cluster of cells into a recognizable tadpole shape, with a tail, a head, and the beginnings of gills.

Stage 2: Hatching and the Early Tadpole

A newly hatched tadpole is an aquatic animal built for one job: eat and grow. It has a rounded body, a long tail with a fin, and gills for breathing under water. It has no legs, and it cannot yet breathe air in the way an adult frog does. Its mouth is small and suited to scraping and filtering food from surfaces and from the water, rather than catching insects.

Early tadpoles often stay close to plants or to the egg mass at first. They are weak swimmers, and they are easy prey. As they feed, they grow quickly. Many tadpoles in pond species feed mainly on algae, bacteria, and fine organic material in the water. That diet is sometimes summarized as herbivorous, but the summary needs care. Tadpoles are opportunists in many species, and some eat insect larvae, detritus, or even other tadpoles. The safe general statement is that most familiar pond tadpoles feed mainly on plantlike and organic material, while diet varies by species and by what is available.

Stage 3: The Growing Tadpole and the First Legs

After a period of feeding and growth, the tadpole begins to show the first visible sign of metamorphosis: small buds at the base of the tail that grow into back legs. The back legs appear first in the familiar sequence. They grow longer, develop joints and webbed feet, and gradually become useful for pushing through water, even while the tail is still the main swimming organ.

Front legs follow later, and their timing has a detail worth noting. In many frogs, the front legs develop under a fold of skin that covers the gills. One front leg may appear before the other as it breaks through that cover. A tadpole with back legs and one front leg is not deformed. It is in the middle of a normal, if uneven looking, transition.

While legs grow, the tadpole still lives in water and still feeds, but its body is preparing for a different life. Its eyes become more prominent, its mouth widens, and its skin and skeleton begin to change. These changes are gradual at first, then faster. The animal is still a tadpole in habitat and in feeding, but it is no longer only a tadpole in shape.

Metamorphosis, the Great Rebuild

Metamorphosis is the most dramatic part of the frog life cycle, and it is also the most misunderstood. It is not a single event, like shedding skin, and it is not a costume change. It is a coordinated rebuild of the body, driven in large part by thyroid hormones, including thyroxine. Those hormones signal tissues to grow, shrink, or be remodeled on a schedule that differs by tissue. That is why legs, lungs, gut, mouth, eyes, and tail do not all change at the same moment.

The breathing system is one of the largest changes. Gills, which extract oxygen from water, are lost, and lungs develop so the animal can breathe air. Many adult frogs also exchange gases through their thin, moist skin, which is one reason adults stay near damp places. Skin breathing does not replace lungs in most frogs, but it supplements them, especially when the frog is resting in water or in a humid place.

The digestive system changes with the diet. The long, coiled gut suited to plant material shortens and remodels for a carnivorous adult diet of insects, worms, spiders, and other small animals. The mouth widens, a tongue develops for catching prey, and the jaw strengthens. The eyes move and enlarge, giving better vision above water. The skeleton, especially the skull and limbs, is reshaped for jumping and for supporting weight on land instead of floating in water.

The tail is the most visible symbol of this rebuild, and its fate is often misstated. The tail does not fall off. Its tissues are broken down by programmed cell death and absorbed into the body, and the stored material helps fuel the final stages of transformation. During this period, the froglet often stops feeding, or feeds very little, because its mouth and gut are in transition and because it is using stored energy. That fasting period is normal in many species, and it is one reason the tail is valuable: it is not waste, it is fuel.

Stage 4: Froglet, a Small Frog With a Tail

A froglet is a young frog that has completed most of metamorphosis but still has a short tail. The name is useful, but it can mislead. A froglet is not a separate species, and it is not a baby in the sense of a helpless newborn. It is a small, nearly complete frog that is finishing one last job: absorbing the rest of its tail.

Froglets stay close to water at first. They can hop and swim, breathe air with lungs, and begin to catch small prey, but they are small, and they dry out faster than adults. Damp ground, dense vegetation, and shade help them survive. They are also still prey for a wide range of animals, from birds and snakes to larger frogs. Size is their main disadvantage. A froglet that survives its first weeks grows quickly, and growth brings better jumping ability, better prey capture, and better resistance to drying.

Stage 5: Adult Frog and the Return to Water

An adult frog is built for life at the boundary between water and land. Powerful back legs allow jumping and swimming. Lungs allow breathing air. A sticky tongue, in many species, allows quick capture of insects and other small prey. Eyes set high on the head allow the frog to see while most of its body stays low in water or vegetation. Skin that must stay moist ties the frog to damp habitats, even when it hunts on land.

Adult diet is carnivorous in most frogs. Insects are the main prey for many species, along with worms, spiders, slugs, and other small invertebrates. Larger frogs take larger prey, including small fish, other frogs, and small vertebrates, depending on species and size. Feeding is opportunistic. A frog usually takes prey it can swallow and that moves within reach, rather than hunting a single preferred food.

Breeding brings adults back to water, and the timing of that return is set by climate and species. In temperate regions, many frogs breed in spring, when warming water and lengthening days signal the season. In tropical regions, breeding often follows rain, when temporary pools fill and food becomes abundant. Males call, females choose, eggs are laid, and the cycle begins again. Some frogs breed once a year, while others breed more than once in a long season.

Why Timing Varies So Much

If the frog life cycle were fixed, a single timetable would work for every species. It does not work, because timing is a response to environment as much as to genetics. Four factors explain most of the variation.

First, species sets the baseline. The American Museum of Natural History notes that the tadpole stage can last for days or years, depending on species and weather, and that American bullfrog tadpoles can take up to two years to metamorphose. The U.S. National Park Service makes the same point in general terms: the length of time an amphibian spends as a larva depends on the species. A bullfrog in a permanent pond can afford a long tadpole life, because the pond will still be there next year. A frog breeding in a temporary pool cannot.

Second, temperature speeds or slows development. Warmer water generally increases metabolic rate and growth, while colder water slows both. That is why tadpoles in a shallow, sun warmed pond may transform faster than tadpoles of the same species in a deep, shaded pond. The U.S. Environmental Protection Agency recorded bullfrog tadpoles in a warm, shallow pond completing metamorphosis in their first season, at about three to three and a half months, in a region where bullfrog tadpoles usually take more than a year. Warmth and falling water together appeared to accelerate development.

Third, food and crowding matter. Tadpoles with plentiful food grow faster and reach metamorphosis sooner, while tadpoles in a crowded or food poor pond grow slowly and may transform at a smaller size. Smaller size at metamorphosis can mean lower survival as a froglet, so there is a trade off. Growing fast is good, but transforming too small is risky. Species differ in how they balance that trade off, and the same species may balance it differently in different ponds.

Fourth, the pond itself may force a decision. If a temporary pond is drying, tadpoles that can speed up metamorphosis have a chance to leave before the water is gone. Tadpoles that cannot speed up may die with the pond. If a pond is permanent and cold, tadpoles may overwinter and finish the next year. Neither outcome is a defect. Both are outcomes of a developmental system that responds to cues in the water, including temperature, food, crowding, and falling water level. Together, these factors explain why two ponds a short distance apart can produce froglets weeks apart, and why a species can look slow in one region and fast in another.

When the Familiar Sequence Does Not Apply

The familiar sequence, egg in water, tadpole in water, froglet, adult, describes many frogs well. It does not describe all frogs, and presenting it as universal would be a serious error. Three kinds of exception show how flexible frog development can be.

The first exception is direct development. AmphibiaWeb notes that frogs in the genus Pristimantis, a very large group found mainly in northern South America, lay eggs on land that develop directly into small froglets, bypassing the tadpole stage. Inside the egg, the embryo builds frog legs, lungs, and a frog body without ever swimming as a tadpole. When it hatches, it is already a tiny frog. AmphibiaWeb also reports a detailed study of Pristimantis latidiscus in Ecuador, in which buried eggs hatched after about 24 to 30 days as froglets, without external gills, using a specialized vascularized tail inside the egg that likely aided gas exchange. That internal tail is not a swimming tail. It is a developmental organ that is absorbed before or around hatching. Direct development frees a frog from standing water for breeding, which helps explain why Pristimantis is so diverse in mountain forests where ponds are scarce. Eggs on land face drying and land predators instead of fish, and they depend on humidity and on the yolk inside the egg for the whole of development, because there is no feeding tadpole stage to gather energy from the pond.

The second exception is parental care that changes where eggs and tadpoles spend their early life. Lemur leaf frogs, described by the Smithsonian’s National Zoo, lay eggs on leaves over water, and the hatchlings drop into the water below; in the Zoo’s reported breeding account the tadpoles completed metamorphosis over 40 to 60 days, while the Zoo’s species profile gives a longer 69 to 98 days after hatching, so timing for this species varies by account and conditions. That is still a tadpole life, but the egg stage is out of the water. In other frogs, a parent may guard eggs, carry tadpoles on its back to water, or carry eggs in a pouch or on its skin. AmphibiaWeb reports male frogs in one Bornean group guarding eggs on the forest floor and later carrying hatched larvae on their backs to slow streams or standing water, where the tadpoles develop until metamorphosis. The details differ by species, but the pattern is the same: parental behavior moves the vulnerable early stage to a safer place, or keeps it with a guard, instead of leaving eggs entirely to chance in open water.

The third exception is timing and place within the familiar sequence. Some frogs lay eggs in foam, on plants above water, or in burrows, and the tadpoles reach water later by dropping, washing in with rain, or being carried. Some tadpoles live in fast streams, tree holes, or small pools in plants rather than ponds, and their bodies reflect that habitat. Stream tadpoles may have strong mouthparts for clinging, while pond tadpoles are built for open water swimming. The stage names stay the same, but the ecology changes, and so does the risk. These exceptions do not make the familiar sequence useless. They make it a starting point. A reader who knows the familiar sequence, and who also knows that direct developers, leaf layers, and tadpole carriers exist, will not be confused by a frog that hatches as a froglet.

Survival, Predators, and Common Misunderstandings

Most frog eggs and tadpoles do not become adult frogs. That sentence is stark, but it is central to understanding frog life history. High egg numbers, in species that have them, are not a sign of waste. They are a response to high loss at every early stage. Eggs are eaten, dried out, or damaged by cold and pollution. Tadpoles are eaten by fish, insects, birds, snakes, and other frogs. Froglets are eaten by birds, snakes, and mammals, and they face drying if they cannot find damp cover.

Several misunderstandings come from the way the life cycle is taught in simplified form. A tadpole is not a baby frog in the sense that a puppy is a baby dog. A puppy grows into a dog without rebuilding its breathing or feeding systems. A tadpole rebuilds them, so the word larva is more accurate. Frogs and toads are not a scientific division. The U.S. National Park Service states this plainly: frogs and toads are common terms, not scientific distinctions, with frogs often used for smooth skinned adults near water and toads for fatter, bumpy skinned adults that spend more time away from water. The tail does not fall off. It is absorbed, and that explains how a froglet can survive a period when it feeds little. Not all frogs live in ponds, and not all frogs need a pond for every stage, as direct developers show. Finally, size does not tell age reliably. A large tadpole may be a young bullfrog tadpole that will spend another year in the pond, while a small froglet may be a fully transformed adult of a small species. Species, not size alone, sets the meaning of what you see.

Frequently Asked Questions

What are the stages in the life cycle of a frog?

In the familiar sequence, the stages are egg, tadpole, tadpole with legs, froglet, and adult frog. Metamorphosis is the process that transforms the tadpole into the frog, overlapping the leg growth and froglet stages. Some summaries group these into three or four stages, which is a difference in grouping, not a different life cycle.

How long does it take a tadpole to become a frog?

It depends on species, temperature, food, and pond type. Many familiar pond tadpoles transform within one season, over weeks to a few months. American bullfrog tadpoles can take up to two years. A single timetable for all frogs would be misleading, so always check the species when a time is given.

What do tadpoles eat?

Most familiar pond tadpoles eat mainly algae, bacteria, and fine organic material in the water. Some species eat insect larvae, detritus, or other tadpoles. Diet varies by species and by what is available, and it changes at metamorphosis, when the animal becomes a predator of insects and other small animals.

Why does a tadpole grow back legs first?

Back legs appear before front legs in the familiar sequence, and front legs develop under the skin fold that covers the gills, so one may appear before the other. Back legs grow first in part because they are the main jumping and swimming legs of the adult, and they need time to grow strong before the animal leaves the water.

What is a froglet?

A froglet is a young frog that looks like a small adult frog but still has a short tail. The tail is absorbed into the body over days to weeks. Once the tail is gone, the animal is a young frog that will keep growing until it reaches adult size and breeding maturity.

Do all frogs have a tadpole stage?

No. Most familiar frogs do, but direct developing frogs, such as many Pristimantis species, hatch from eggs laid on land as tiny froglets, with no free swimming tadpole stage. Other frogs change the egg stage, for example by laying eggs on leaves over water, while still having a tadpole stage after hatching.

Why do frogs return to water as adults?

In the familiar sequence, adults return to water to breed because eggs and tadpoles need water to survive and develop. Even adults that hunt on land usually stay near damp places, because their skin must stay moist and because breeding ties them to water. Direct developers are an exception, because their eggs develop on land.

What happens to the tadpole tail?

The tail is not shed or dropped. Its tissues are broken down and absorbed into the froglet body, providing energy during a period when feeding is reduced. This programmed breakdown is part of metamorphosis, driven by the same hormonal changes that remodel the rest of the body.

How can you tell a tadpole from a froglet?

A tadpole swims with a tail, breathes with gills, and has no legs at first, then grows legs while still mainly aquatic. A froglet has four legs, breathes air with lungs, looks like a small frog, and has only a short tail remnant. The change is gradual, so animals in the middle show features of both stages.

Sources & references

• Smithsonian's National Zoo and Conservation Biology Institute: lemur leaf frog breeding, eggs on leaves over water; Zoo breeding account 40 to 60 days for metamorphosis, species profile 69 to 98 days after hatching.
• U.S. National Park Service, Life Cycles: amphibian larval timing by species, frogs and toads as common terms rather than scientific distinctions, and the shift from gills and tail to legs and lungs.
• American Museum of Natural History, Tadpoles: tadpole stage lasting days to years by species and weather, American bullfrog tadpoles taking up to two years to metamorphose, and bullfrog egg numbers.
• AmphibiaWeb, Amphibian Facts: Pristimantis as a species rich frog genus whose eggs are laid on land and develop directly into small froglets, bypassing the tadpole stage.
• AmphibiaWeb, News of the Week: Pristimantis latidiscus egg burying, hatching after about 24 to 30 days as froglets, and male brood care and tadpole carrying in a Bornean frog group.
• U.S. Environmental Protection Agency, Science Inventory: bullfrog tadpole metamorphosis timing from about three months in a warm pond to up to three years in cooler eastern United States conditions, with temperature as a key factor.
• Lumen Learning, Biology for Majors II: amphibian life cycle, front legs formed under the gill sac, and thyroxin in tail resorption; thyroid-hormone tail-resorption mechanism as described in the peer-reviewed tail-resorption literature.