These are non-native frogs which often breed (and call) during the summer months. The term 'green frog' encompasses a complex of similar species including the marsh frog Pelophylax ridibundus, edible frog P. esculentus and pool frog P. lessonae. The pool frog is a native species which became extinct in UK and has since been reintroduced to East Anglia. Green frogs are variable in colour but often have a yellow stripe down the back; they usually lack the 'mask' behind the eye that the common frog has. The nose is relatively pointed and the eyes are closer together than the common frog. Unlike America bullfrogs, another non-native species, green frogs have a pair of conspicuous dorsolateral ridges running the length of the body. When calling, green frogs inflate a pair of vocal sacs, rather like a pair of balloons, one either side of the head; all have a loud call which is often likened to ducks quacking. Marsh frogs can be up to 15cm long but other species smaller.