Rana temporaria, commonly known as the European common frog, is a widespread amphibian species found across Europe and parts of northwestern Asia, extending as far north as the Arctic Circle. It is one of the most recognized amphibians in the region.
Physical Characteristics and Natural Environment
The European common frog typically measures between 6 to 9 centimeters in length, with females generally larger than males. Its skin is smooth and moist, displaying varied coloration (brown, olive-green, grey, or reddish-brown), often with darker spots. A distinctive dark patch, often triangular, is usually present behind each eye, covering the eardrum.
This species possesses robust bodies with long hind legs, well-suited for powerful jumps on land and efficient swimming. Their eyes have horizontal pupils and are positioned on the sides of their head. During the breeding season, males can develop bluish patches on their throat and back, while females may show reddish hues on their sides.
Rana temporaria is highly adaptable, thriving in diverse damp habitats like woodlands, grasslands, gardens, and various freshwater bodies (ponds, lakes, swamps, ditches). They are frequently found near stagnant or slow-moving water, important for their life cycle.
Life Cycle and Breeding Habits
Breeding typically occurs in early spring, from February to March in warmer lowlands and as late as June in northern or high-altitude regions. A cold spring can initiate this behavior. Males usually arrive at breeding sites first, attracting females with low-pitched growling croaks.
Males grasp females in an embrace called amplexus, using nuptial pads on their thumbs. This embrace can last for several days until the female lays her eggs. Females deposit large clumps of eggs, known as frogspawn, containing 670 to over 4,000 eggs, often attached to submerged vegetation in shallow, still freshwater.
The eggs, enclosed in a gelatinous envelope, swell upon contact with water, providing insulation. After 10 to 40 days, depending on temperature, eggs hatch into tadpoles. Initially, tadpoles feed on the frogspawn jelly and an internal yolk-sac.
Within days, tadpoles develop mouthparts, gills, and eyes, feeding on algae and pond plants. As they grow, they develop hind legs first, then front legs around 10 to 11 weeks. During metamorphosis, gills are replaced by lungs, and tails gradually shrink and are absorbed.
Transformation into froglets is largely complete by 12 to 14 weeks, when they leave the water for nearby vegetation. Young froglets double in size by autumn and reach sexual maturity in approximately three years, returning to their birth ponds to breed.
Diet and Daily Activities
The European common frog is carnivorous, primarily feeding on small invertebrates like insects, slugs, snails, spiders, and worms. They detect worms by smell and use their long, sticky tongue to capture and swallow prey whole.
While seen during the day, especially during breeding, common frogs are generally nocturnal or crepuscular, most active during evening and nighttime. During the day, they typically seek shelter in damp, shady areas like under vegetation or rocks.
As colder months approach, Rana temporaria hibernates, usually from late October to January in the British Isles, extending longer in northern regions. They find shelter in frost-free locations like compost heaps, under logs, in stone walls, or submerged in ponds. Frogs absorb oxygen directly through their permeable skin, allowing them to breathe underwater during hibernation.
Conservation and Challenges
The European common frog is classified as ‘Least Concern’ on the IUCN Red List, indicating a stable overall population. Despite this, local populations can decline and are vulnerable to human impacts.
Challenges include habitat loss (urbanization, agricultural expansion, destruction of breeding ponds). Pollution, such as from herbicides, also affects local populations. Diseases, like the pathogenic chytrid fungus, threaten amphibian populations globally and have been found in Rana temporaria.
Road mortality is another factor in localized declines, especially during breeding migrations when frogs cross roads to reach spawning grounds. While widespread, ongoing monitoring and protection of specific habitats remain important for maintaining healthy populations.