American Bull Frog (Lithobates catesbeianus)
The North American Bullfrog is a non-native species that has successfully bred in the wild in the UK. This animal is a significant threat to native amphibians and sightings should be reported immediately. These frogs are huge compared with our native frogs and will eat amphibians and other animals of similar size. Bullfrogs have a large eardrum, at least as big as the eye, and a fold of skin that runs over the top of the eardrum and down towards the flank. They were originally introduced to Britain through the pet trade and probably found their way into the countryside when owners decided to get rid of spawn or tadpoles in nearby ponds. In 1999 they bred for the first time at a site in England and have since been controlled by Natural England.
|Identification||Adults up to 25 cm in length: largest frog encountered in the UK. Green or brown skin, often with dark stripes on hind legs. Very large eardrum (tympanum): at least as large as the eye in females and twice the size of the eye in males. Fold of skin over the top of the eardrum. No ridges along the back. They have a very large single vocal sac under the chin. Bullfrog tadpoles are very large (up to 15cm).
Oval, horizontal pupil.
Call: deep, low-pitched bellow. Reminiscent of calls made by cattle. A deep bass “gr-rum” or “jug-o-rum”.
|Distribution||Non-native species. Native to North America. Probably introduced to the wild in the UK via the pet trade. Potentially very damaging to native fauna; currently controlled by Natural England. Rarely encountered in the UK.|
|Ecology||Strongly aquatic. Found near the edges of ponds and marshes. Opportunistic feeders and will eat anything smaller than themselves. Cannibalism is common. Breeding season begins in spring and lasts throughout early summer. Breed in densely vegetated shallow ponds. Very large tadpoles: up to 15 cm.
Eggs are laid on the surface of the water and one clutch can consist of up to 20,000 eggs.
|Predators and other threats||The American Bullfrog is extremely large and therefore less susceptible to predation compared to the native Common Frog. However, in the UK it is still likely to be prey for large birds and mammals such as Herons and Badgers. The tadpoles and juvenile Bullfrogs are likely to be predated upon by fish, snakes, birds and mammals. The global population of the American Bullfrog is thought to be increasing and has been extremely successful in establishing populations outside it’s natural range, aided by exportation for the pet and food trades.|
N.B. The release of exotic species into the wild is a criminal offence under the Wildlife and Countryside Act 1981.