Appearance
Adult common frogs have a body length of 6 to 9 centimetres (2.4 to 3.5 in) and their backs and flanks vary in colour, with olive green grey-brown, brown, olive-brown, grey, yellowish or rufous possible. However, common frogs are known to be able to lighten and darken their skin in order to match their surroundings. It is also not unknown for more unusual colouration- both black and red individuals have been found in Scotland, and male common frogs have been known to turn greyish blue in the mating season (video on page). Additionally, albino common frogs have been found with yellow skin and red eyes. Their average weight is 22.7 g (0.80 oz). Females are usually slightly larger than males.
Common frogs' flanks, limbs and backs are covered with irregular dark blotches and they usually sport a chevron-shaped spot on the back of their neck. Unlike other amphibians, common frogs generally lack a middorsal band, and when they have one, it is comparatively faint. In many countries the moor frogs do have a light dorsal band which easily distinguishes them from common frogs. The frogs' underbellies are white or yellow (occasionally more orange in females) and can be speckled with brown or orange. Common frogs have relatively short hind legs and possess webbed feet. The legs of the agile frog are much longer which distinguishes them from common frogs along with the agile frog's fainter colouration. Their eyes are brown with transparent horizontal pupils, and they have transparent inner eyelids to protect their eyes while underwater, as well as a 'mask' which covers their eyes and eardrums.
Males are distinguishable from females due to hard swellings (called nuptial pads) on their first finger. These are used for gripping females during mating. Also, during the mating season, males' throats often turn white. A final differentiation can be the colour—during the mating season, males are generally light and greyish in colour, whereas the female is browner, or even red.
The mating season is short, just a week in March after which the frogs move back to their terrestrial habitat.
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