Amphibians
Common Frog
Rana temporaria · also called European common frog, grass frog
The common frog is the frog most Europeans picture — the smooth brown amphibian that appears in garden ponds each spring, fills them with croaking and clumps of spawn, and then spreads out through the damp grass for the rest of the year. It is the most widespread amphibian in northern Europe and a familiar barometer of the health of ponds and wet places.
Overview
Common frogs live almost everywhere in Europe with fresh water and damp ground, from lowland farmland and gardens to mountain bogs above the tree line and the Arctic coast of Scandinavia. Outside the breeding season they are largely terrestrial and nocturnal, foraging in vegetation, and they never stray far from moisture because they lose water quickly through the skin. They shelter by day under logs, stones, and leaf litter.
Skin that breathes
Like all frogs, the common frog gets oxygen three ways — through its lungs, the lining of its mouth, and its skin. The skin route becomes vital in winter: a hibernating frog on the bottom of a pond can absorb enough dissolved oxygen through its skin, at its very low winter metabolic rate, to survive for months without surfacing. That same permeable skin is why frogs are so sensitive to pollution and to drying out.
Colour and camouflage
Common frogs are extremely variable in colour — brown, grey, olive, yellow, orange, or almost brick red — usually with a dark “mask” behind the eye and dark bars on the legs. Individuals can lighten or darken over a few hours to match their surroundings and their temperature.
Breeding
Common frogs are explosive breeders. On the first mild, wet nights of late winter or early spring, adults migrate — sometimes a considerable distance, and often across roads — back to the exact pond where they hatched. Males croak from the water and grip females in “amplexus,” and each female lays a floating clump of up to 2,000 eggs. Frost can kill the earliest spawn, but laying early gives the tadpoles the longest possible time to develop before summer.
Tadpoles start as algae-grazers and become increasingly carnivorous — even cannibalistic — as they grow, transforming into tiny froglets and leaving the water in early summer.
Status
The common frog is listed as Least Concern, but its numbers are falling in parts of its range. In the UK, an introduced ranavirus has caused severe die-offs of adult frogs in garden populations since the 1990s. More broadly, the loss and pollution of ponds, the drainage of wet meadows, road deaths during migrations, pesticides, and the worldwide spread of the chytrid fungus are all pressures. Because the species is so tied to a home pond, protecting and creating small clean waterbodies is the single most effective way to help it.
Common Frog: common questions
How does a common frog survive a freezing winter underwater?
It hibernates, and for part of that time it barely breathes with its lungs at all. Sitting in mud or among leaves at the bottom of a pond, the frog takes up oxygen directly from the water through its skin, which is rich in blood vessels. Its metabolism drops so low that this is enough. If the pond ices over completely for a long time, dissolved oxygen can run out and cause "winterkill," where frogs suffocate — one reason ponds with some moving water or an unfrozen patch are better for them.
What is the difference between frogspawn and toadspawn?
Common frogs lay their eggs in a rounded, jelly-like clump that floats near the surface, often several clumps merging into a raft. Common toads lay theirs in long double strings wound around submerged plant stems. Frog tadpoles are dark gold-brown and speckled; toad tadpoles are jet black and often shoal in dense groups.
Why do frogs return to the same pond every year?
Common frogs show strong "breeding-site fidelity" — adults migrate back, sometimes over a kilometre and across roads, to the pond where they hatched, guided by memory, the smell of the water, and possibly the calls of frogs already there. This is why garden ponds fill with frogs each spring, why frog "toad patrols" help amphibians cross roads on migration nights, and why losing a single pond can wipe out a local population even if other water is nearby.
Are common frogs declining?
Across Europe as a whole the species is still classed as Least Concern, but there are real local declines. In Britain, an introduced strain of ranavirus has caused mass die-offs of adult frogs in gardens since the 1990s, and elsewhere the drainage and pollution of ponds, the loss of damp meadow and hedgerow habitat, road mortality, pesticide use, and the global amphibian chytrid fungus all take a toll.