Rana arvalis in the context of Antifreeze protein

The common frog or grass frog (Rana temporaria), also known as the European common frog, European common brown frog, European grass frog, European Holarctic true frog, European pond frog or European brown frog, is a semi-aquatic amphibian of the family Ranidae, found throughout much of Europe as far north as Scandinavia and as far east as the Urals, except for most of the Iberian Peninsula, southern Italy, and the southern Balkans. The farthest west it can be found is Ireland. It is also found in Asia, and eastward to Japan. The nominative, and most common, subspecies Rana temporaria temporaria is a largely terrestrial frog native to Europe. It is distributed throughout northern Europe and can be found in Ireland, the Isle of Lewis and as far east as Japan.

Common frogs metamorphose through three distinct developmental life stages — aquatic larva, terrestrial juvenile, and adult. They have corpulent bodies with a rounded snout, webbed feet and long hind legs adapted for swimming in water and hopping on land. Common frogs are often confused with the common toad (Bufo bufo), but frogs are easily distinguished by their longer legs, hopping movements, and moist skin, whereas toads crawl and have a dry 'warty' skin. The spawn of the two species is also different, with frogs laying their eggs in clumps and toads in long strings. The common frog is very similar to its close relative the moor frog (Rana arvalis). Where both species occur together the most reliable way to tell them apart is by looking at their metatarsal tubercles, a small spur on the hind feet next to the innermost toe: in common frog it is soft and small, less than a third of the length of the innermost toe, while in moor frog it is hard and approximately half the length of the innermost toe. Common frog and moor frog also have different calls, and for a short period during the breeding season moor frog males may become blue in color, while common frog males at most get a faint blueish tint.