The marsh frog is the largest European frog, with a body length of up to 15 centimetres. Its colouration varies. In general, it has a green back, occasionally with dark spots and/or a faint vertebral ridge. Males have prominent vocal sacs at the side of the mouth, which appear grey when inflated in contrast to the whitish appearance of the vocal sacs of other species.
Marsh frogs live in different types of wetland up to altitudes of 1,500 metres. They can be found in Central Europe as far as the Urals, and inAsia Minor and some parts of North Africa.
Aquatic and predatory, the marsh frog spends most of its time near rivers or marshes, where it hunts. The mating period is in April and May, when males call throughout the night. Females lay between 700 and 13,000 eggs in oval groups attached to water vegetation. The marsh frog hibernates under the water. It feeds mainly on insects, but also on other frogs or fish, and sometimes even on small rodents. It captures its prey with its elastic tongue.