The common frog (Rana temporaria) is the most widespread species of amphibian in the Clyde catchment area, encountered in both urban and rural settings.
Common frogs have smooth, moist skin. Adults can grow to 9cm (nose to vent). They are generall a shade of olive green through brown, with a dark patch (or 'mask') behind the eyes. Frogs often have bands of darker striping on the back legs. Many individuals hae irregular dark markings on the back and flanks. Colouration is extremely variable: yellow, pink, red, orange, and black individuals have been reported. The females can sometimes develop a reddish colour during the breeding season whereas males tend to turn greyish brown with a grey-blue vocal sac on their chin.
Both males and females emerge from hibernation and head straight to ponds to breed in February to March most years. Males are smaller than females and grasp the feales behind the forelimbs, remaining clasped in what is termed "amplexus" for up to several days or weeks prior to spawning taking place. Frog spawn is laid in clumps containing between 1,000-2,500 gelatinous eggs containing black embryos typically in shallow areas of water bodies. Very young tadpoles are black but as they develop they become more brown and speckled with gold colouration making them distinguishable from the very similar common toad (Bufo bufo) tadpoles which remain black throughout development. Tadpoles usually begin to emerge from their ponds between June and August but can be as late as September or October. In particularly cold years, tadpoles may overwinter and metamorphose early in the next season.
In the wild, common frogs can live for up to 8 years but they have many predators including birds of prey, herons, foxes, stoats, badgers, and others which often results in a much reduced lifespan. Tadpoles are also eaten by birds and larger aquatic fauna such as beetle and dragonfly larvae as well as older tadpoles, newts, and fish. Common frogs are largely terrestrial outside the breeding season, and can be found in a variety of damp habitats ranging from grassland and woodland to high up mountains where suitable breeding sites can be found. They breed in puddles, ponds, lochs, and canals preferring aeas of shallow water.
Common frogs do not feed all throughout the hibernation season but when they are active they will feed on any moving invertebrates of a suitable size, such as insects, snails, slugs, and worms which they catch with their long, sticky tongues. Adult frogs feed entirely on land, whereas younger frogs will also feed in the water. Tadpoles are herbivorous and feed on algae but become carnivores late on in development.
In Britain, common frogs are protected by law under Section 9(5) of the Wildlife and Countryside Act 1981 (As amended). This prohibits sale, barter, exchange, transporting for sale, and advertising to sell or to buy. Populations can be threatened in areas where breeding ponds are disturbed or polluted.
Erik Paterson, CARG Secretary