Short description of Lithobates catesbeianus, American Bullfrog

Bullfrogs are up to twice the length of the native common frog, and draw attention by their loud, deep calls. Their ear drum is obviously larger than the eye, with a conspicuous dark outer ring. The lack of skin folds along the back, and the single vocal sac positioned beneath the chin, help to distinguish this from other non-native frogs in GB. Tadpoles grow to up to 15 cm.

Impact summary: Lithobates catesbeianus, American Bullfrog

The bullfrog is one of the most harmful invasive non-native species. It both competes with and eats native amphibians, and carries a disease that has contributed to worldwide amphibian decline and to several global extinctions.

Habitat summary: Lithobates catesbeianus, American Bullfrog

It occupies any type of still or slowly moving water, especially where aquatic and bank vegetation are abundant, in the native range from sea level to 2000m.  Calm water that will not dry out and deep pools in rivers and streams are preferred.

Overview table

Environment	Terrestrial and Freshwater
Species status	Non-Native
Native range	Eastern United States, Far East United States
Functional type	Predator
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record	Bexhill (14)
Date of first record	1996

Origin

The bullfrog is native to eastern North America but has been introduced west of the Rockies and to around 25 countries worldwide during the past two centuries. At least 25 separate introduction attempts have been made in Europe.

First Record

The first single bullfrog in GB was found in East Sussex in 1996, and breeding was first noted at the same site in 1999.

Pathway and Method

Bullfrogs have been deliberately released as unwanted pets and have escaped from garden ponds where they had been confined as tadpoles. Others have been imported accidentally with fish stocks or aquatic plants. Introductions outside GB have also been made for biological control of insect pests and as stocking for human consumption.

Species Status

The initial population was successfully eradicated by 2004, after the removal of at least 9,000 animals. In 2006, a further breeding population was discovered in Essex: 100 animals were removed in 2007 but only five in 2008, suggesting that the population had already been greatly reduced. Presence, but not breeding, has been noted at a few further sites in SE England.

Dispersal Mechanisms

Natural dispersal is both terrestrial and via rivers, covering whole water catchments. Froglets cross arid country between ponds and are known to have travelled at least six miles in a few weeks.

Reproduction

In southwest France, the breeding period lasts from May until early September. Tadpole development takes 1–2 years; because of the long development period, pools that might dry out are generally avoided.

Known Predators/Herbivores

Predators include carnivorous fishes and probably some mustelids and herons. The main source of predation, in high-density areas, appears to be cannibalism. There are no known predators of adult bullfrogs in GB.

Resistant Stages

Bullfrogs hibernate underwater between October and March.

Habitat Occupied in GB

Bullfrogs might be found in GB in any freshwater pool or backwater that is unlikely to dry out.

Breeding populations discovered in East Sussex and Essex have been removed.

Environmental Impact

This species feeds day and night on a wide range of prey, including amphibians, fishes, small mammals, ducklings and small bird species, molluscs, crustaceans and insects. Both predation and competition may adversely affect populations of native frogs, toads and newts. American bullfrogs and other non-native amphibians may carry the chytrid fungus Batrachochytrium dendrobatidis, and can spread the disease chytridiomycosis to native amphibians.

Health and Social Impact

None known.

Economic Impact

The cost so far of control measures and monitoring in GB has been estimated to be more than £100 000.

Identification

NNSS ID Sheet - https://secure.fera.defra.gov.uk/nonnativespecies/index.cfm?sectionid=47

Biology, ecology, spread, vectors

Banks, B., Foster, J., Langton, T. & Morgan, K. (2000) British Bullfrogs? British Wildlife, 11, 327–330.

Stumpel, A.H.P. (1992) Successful reproduction of introduced bullfrogs Rana catesbeiana in northwestern Europe – a potential threat to indigenous amphibians. Biological Conservation, 60, 61–62.

Management and impact

Daszak, P., Strieby, A., Cunningham, A.A., Longcore, J.E., Brown, C.C. & Porter, D. (2004) Experimental evidence that the bullfrog (Rana catesbeiana) is a potential carrier of chytridiomycosis, an emerging fungal disease of amphibians. Herpetological Journal, 14, 201–207.

Fisher, M.C. & Garner, T.W.J. (2007) The relationship between the introduction of Batrachochytrium dendrobatidis, the international trade in amphibians and introduced amphibian species. Fungal Biology Reviews, 21, 2–9.

Garner, T.W.J., Perkins, M., Govindarajulu, P., Seglie, D., Walker, S.J., Cunningham, A.A. & Fisher, M.C. (2006) The emerging amphibian pathogen Batrachochytrium dendrobatidis globally infects introduced populations of the North American bullfrog, Rana catesbeiana. Biology Letters, 2, 455–459.

Lannoo, M. ( ed) (2005) Amphibian declines - the conservation status of United States species. University of California Press, Berkeley, CA.

General

Ficetola, G.F., Coïc, C., Detaint, M., Berroneau, M., Lorvelec, O. & Miaud, C. (2007) Pattern of distribution of the American bullfrog Rana catesbeiana in Europe. Biological Invasions, 9, 767–772.

Lever, C. (2009) The Naturalized Animals of Britain and Ireland. New Holland Publishers, London.

Spitzen – van der Sluijs, A.M. & Zollinger, R. (2010) Literature review on the American bullfrog Rana catesbeiana (Shaw, 1802). Stichting RAVON, Nijmegen, the Netherlands. full text