American Bullfrog
Identification: Large frog. Length up to more than 20 cm, usually 10-18 cm. Pupil horizontal, elliptical. Colour on the back brown to olive green, sometimes with dark spots. In brown animals, the head usually is still greenish. No light greenish stripe over the middle of the back. Belly is whitish, mostly with grey spots. Eardrums large, in females 1 to 1.5 times as large as the eye, in males 2 times as large as the eye. No dorsolateral folds on border between flank and back, but they have an arched fold starting at the eye, curving around the eardrum (on the upper side), up to the base of the front leg. Strong webbing between the toes. Males have dark nuptial pads on the thumbs. The throat is yellowish in males and more cream coloured in females. Singular vocal sac beneath the chin.
Range: Originates from eastern north America. In the past, they were imported in large numbers to Europe as a pet, sold especially in garden centres for garden ponds. Escaped or released massively. In some places in Europe, breeding populations have been established. They form a threat for, besides others, the native frogs because they eat them, but also because they eat the same prey. In the British Isles, breeding occurred at a site on the Sussex and Kent border, and efforts were made to exterminate the species. Vigilance is still required, as there have been reports of accidental introductions of tadpoles included with consignments of aquatic plants.
Habitat: In their original range, found in all types of water. In Europe, they have a preference for larger, still, sunny, shallow waters with dense vegetation. Also the shallow edges of lakes and rivers are suitable for them.
Habits: A real aquatic frog, stays in or very close to water. Active by day and night, but most activity after dark. Newly produced clumps of spawn float as a flat mass on the water surface, but soon they sink. They contain 10,000 to 20,000 eggs. After 7-12 days, the larvae hatch, when they are 1.2-1.5 cm long. Larvae are brownish green on the back; the belly is white. The larvae often metamorphose after more than 2 years. They sometimes grow up to more than 16 cm long. Newly metamorphosed frogs are 2.5 to 6 cm long and they mature after 2-3 years. Bull Frogs feed on anything that moves and fits in their mouth, such as frogs (other species or smaller individuals of their own kind), small water snakes and chicks of water birds. Hibernates dug into the soil on land or in the mud under water.
How to find: Best chance by going towards their specific call, but usually they dive quickly under water when approached.
Call: Very loud (but not louder than, for example, the Marsh Frog). A repeated low, grunting "whrumm". Resembles the moo of cows or bulls. Very penetrating, can be heard up to more than a kilometre. They can also produce an alarm call.