Common Frog (Rana temporaria): Facts, Habitat and Life Cycle

Appearance: how to recognize a common frog

The common frog has a plump body, a rounded snout, smooth moist skin and long, powerful hind legs with webbed toes. Its color varies more than almost any other European frog. Most are olive, gray-brown or brown, but yellow, reddish, orange and almost black frogs all occur, and a single frog can turn lighter or darker within hours to match its background.

The back and legs are usually marked with irregular dark blotches, and the hind legs have dark crossbars. The most reliable field mark is the dark brown patch, often called the mask, that runs from the eye back over the round eardrum (tympanum). A ridge of skin, the dorsolateral fold, runs down each side of the back. The belly is white, cream or yellow, often speckled, and in females it can be orange.

Males are slightly smaller and have dark, rough swellings called nuptial pads on their thumbs, which help them grip females. In the breeding season they often look pale gray or faintly bluish, with a white throat. Females are larger and fuller-bodied, and are often browner or redder.

In parts of central and eastern Europe the common frog can be confused with the moor frog (Rana arvalis) and the agile frog (Rana dalmatina). The moor frog has a pointed snout and a hard spur on the hind foot, and breeding males can turn bright blue; the agile frog has even longer legs and paler markings.

How big is a common frog?

Adults usually measure 6–9 cm (2.4–3.5 in) from snout to vent, the standard frog measurement that leaves out the legs. Large females occasionally reach about 10 cm (4 in). The average weight is roughly 23 g (0.8 oz), about the weight of four sugar cubes, with egg-laden females in spring heavier than males.

Froglets are tiny when they leave the pond, often only about 1 cm (0.4 in) long, and they take two to three years to reach adult size. Frogs in cold mountain and northern populations grow more slowly but may end up just as large because they live longer.

Habitat and range

The common frog lives across most of Europe, from Ireland and Britain east to the Ural Mountains and on into western Siberia and northern Kazakhstan. It is one of very few amphibians found north of the Arctic Circle in Scandinavia and northern Russia. It is missing from most of the Iberian Peninsula, southern Italy and the southern Balkans, where summers are too hot and dry, but it occurs in the cooler mountains of northern Spain and in the Alps and Pyrenees at well over 2,000 m (6,600 ft).

On land it needs damp cover: rough grassland, hedgerows, woodland, marshes, bogs, moorland, mountain meadows and gardens. For breeding it prefers shallow, still, fish-free water that warms quickly in spring, such as small ponds, ditches, flooded meadows and the edges of lakes. In Britain, garden ponds have become one of its most important breeding sites, which is why many people meet their first frogs in their own backyard.

Diet: what do common frogs eat?

Adult common frogs are carnivores and opportunistic hunters. They eat almost any small, moving animal that fits in their mouth: beetles, flies, crane flies, caterpillars, moths, spiders, woodlice, slugs, snails and earthworms. Larger frogs take larger prey, and the diet follows the seasons, so crane flies and caterpillars are especially important in summer.

A common frog usually hunts by sitting still in damp vegetation, mostly at dusk and at night, and waiting for prey to come close. Then it flicks out its sticky tongue, which is attached at the front of the mouth, and pulls the victim in. Frogs swallow food whole and may blink while swallowing, pressing their eyeballs down to help push food toward the throat.

Tadpoles are very different. They scrape algae and soft plant material with tiny horny teeth around the mouth, and they also scavenge on dead animals. As their legs develop they become more carnivorous. Adults do not usually feed while gathered in ponds to breed.

Behavior and seasons

Outside the breeding season, common frogs are solitary and spend most of their time on land, hiding by day under logs, stones and dense plants and coming out to hunt on damp evenings. They are good swimmers and strong jumpers, and a frightened frog escapes with a series of long, zigzag hops.

In cold weather they become inactive. In Britain most frogs hibernate from about late October or November until January or February, while in the far north and high in the mountains they may be dormant for six to eight months. Some overwinter on land under logs, leaf litter, compost heaps or in burrows, and others, mostly males, spend the winter resting at the bottom of ponds, taking in oxygen through their skin. Common frogs cannot survive being frozen solid, unlike the North American wood frog, so they must find a spot that stays above freezing. Read more in Where do frogs go in winter?

Males call during the breeding season with a soft, low purring or grunting croak, quieter than the calls of many frogs. A chorus of hundreds of males can still be heard from a distance on a mild spring night.

Reproduction and life cycle

The common frog is an “explosive breeder”. When the weather turns mild and wet in late winter or spring, adults migrate to their breeding ponds, often the same ones each year, and breeding is over within a few days to two weeks. Males arrive first and grab any female they can, clasping her from behind in a mating hold called amplexus.

The female lays a rounded clump of frogspawn in shallow water, usually containing from a few hundred to about 4,000 eggs, and the male fertilizes them as they are laid. Females often lay close together, so a single pond can hold a large raft of spawn. Packing the eggs together helps them absorb the sun’s warmth, which speeds up development.

The eggs hatch after about 10 days to 3 weeks, depending on temperature. The tadpoles feed and grow through the spring, develop hind legs and then front legs, and absorb their tails. Metamorphosis usually takes 10–16 weeks, and tiny froglets leave the water in early summer, often in large numbers after rain. Frogs become able to breed at about 2–3 years old, later in cold northern and mountain populations. The full sequence is explained in How do tadpoles turn into frogs?

Lifespan

Most common frogs die young. Of the thousands of eggs a female lays, only a tiny fraction survive to become adults, because tadpoles and froglets are eaten by so many predators. Adults that do survive commonly live a few years, and some reach 8 years or more. Scientists estimate the age of frogs by counting growth rings in their bones, a method called skeletochronology, and the oldest wild common frogs found this way, in cold mountain populations, were about 14 years old. See How long do frogs live? for comparisons with other species.

Predators and threats

Frogspawn and tadpoles are eaten by fish, newts, diving beetles, dragonfly larvae, water boatmen and ducks. Adult frogs have a long list of enemies, including gray herons, storks, birds of prey, crows, gulls, otters, polecats, stoats, badgers, foxes and grass snakes. Domestic cats kill many frogs, and large numbers are run over on roads during the spring migration.

The biggest long-term threats are the loss of ponds and wetlands, farm drainage, pollution and the splitting of habitats by roads. Disease is also serious. Ranavirus, a virus that causes skin ulcers and internal bleeding, has caused repeated mass deaths of common frogs in British garden ponds since the late 1980s. To avoid spreading disease, amphibian charities advise people not to move frogspawn, tadpoles or frogs between ponds.

Conservation status

The IUCN Red List classifies the common frog as Least Concern, because it is common across an enormous range and tolerates many kinds of habitat, including gardens and farmland. The assessment dates from 2008 and notes local declines in parts of the range.

In the European Union the species is listed in Annex V of the Habitats Directive, which means countries must make sure that any taking from the wild does not harm its conservation status. In Great Britain it is protected against sale under the Wildlife and Countryside Act 1981, and many countries in continental Europe give it wider legal protection.

Myths and facts

Myth: Frogs live in ponds all year. Common frogs only visit ponds for a few weeks to breed, and some overwinter there. For most of the year they live on land, sometimes hundreds of meters from water.

Myth: Frogs and toads are the same thing. The common frog and the common toad often share ponds, but they belong to different families and differ in skin, legs, movement and spawn. See frog vs toad for the full comparison.

Fact: Frogs can change color. A common frog cannot change color as fast as a chameleon, but it can noticeably lighten or darken in a few hours depending on light, temperature and background.

Fact: Common frogs are not freeze-tolerant. Unlike the North American wood frog, a common frog dies if its body freezes solid, which is why it needs a frost-free hiding place or the bottom of a pond in winter.

Relationship with people

For many Europeans the common frog is the most familiar amphibian of all. Watching frogspawn turn into tadpoles and froglets is a classic spring activity for schoolchildren, and gardeners welcome frogs because they eat slugs and other invertebrates. Wildlife groups in Britain and elsewhere run spawn surveys and encourage people to dig wildlife ponds without fish, which has helped frogs in towns where other wetlands have disappeared.

The species has also played a large role in science. Because it is common and easy to find, it has long been used to study embryo development, hormones and the effects of climate on breeding dates. Because the first frogspawn is such an obvious sign of spring, its date is recorded by volunteer nature-calendar schemes and used to follow how the seasons are shifting.