Taxonomy
Lithobates catesbeianus | American Bullfrog | Tarbhfhrog Meiriceánach
Distribution
Status
Conservation status
Least concern
Legal status
Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted).
Regulated invasive species of Union concern under the European Regulation on the prevention and management of the introduction and spread of invasive alien species [1143/2014].
Invasiveness
Invasive species - risk of High Impact
Introduction pathways - 1
Escape from Confinement, Transport Contaminant, Transport Stowaway, Corridor, Unaided
Introduction pathways subclass - 1
Pet/aquarium species
Introduction pathways - 2
Transport Contaminant
Introduction pathways subclass - 2
Other means of transport
Invasive score
18
NAPRA Ireland risk assessed
Yes. This species underwent a Non-native species APplication based Risk Analysis in 2014.
Overall risk of this species to Ireland is categorised as: MAJOR with a MEDIUM level of confidence.
Overall conclusion summary: Entry is only moderately likely as importing the species into Europe has been prohibited since 1997. However, it occurs in large numbers in other EU member states, from which smuggling is possible. The species is occasionally kept in captivity and escapes are possible. The species also occurs in close proximity with fish traded internationally, and unintentional releases may be possible via this pathway.
Establishment is likely once the species arrives in the wild under the following conditions: at least one frog of each sex in founder stock; suitable breeding pond present nearby; low vigilance toward invasive amphibians in the local area. Least likely in areas where there are few ponds or ponds are very small and fragmented by large areas of built land.
Lithobates catesbeianus is known to spread rapidly when habitat conditions are favourable. Much of lowland Ireland outside highly urbanised areas could be at risk.
Most important potential environmental impacts are reduction in
abundance and diversity of amphibian fauna, and possibly other fauna,
through predation, competition and disease transmission. Economic and
social harm is likely to be minimal.
View the full risk assessment: http://nonnativespecies.ie/wp-content/uploads/2014/03/Lithobates-catesbeianus-American-Bullfrog.pdf
Species Biology
Identification
Adults
Large green, olive green or brownish frog that can be up to 20cm long and weigh 0.5kg (EEA, 2012). Legs banded or covered in dark patches (CABI, 2014). Has a large tympanum (eardrum) with a dark outer rim (Marchant, 2012) and smooth skin with few wrinkles or warts (CABI, 2014). Curved ridge of skin from the eye around the back of the tympanum and extending to the shoulder (NNSS, undated). The female's tympanum is the same size as the eye and the throat is a cream colour. In males the throat is yellow and the tympanum is larger than the eye (NNSS, undated).
The male makes a loud call that is reminiscent of cattle bellowing (NNSS, undated).
Tadpoles
Tadpoles are brown or olive green with black spots (CABI, 2014). Can be 15cm long (NNSS, undated).
Ecology
The bullfrog is a voracious feeder consuming anything that will fit in its mouth including insects, molluscs, amphibians, reptiles, birds and small mammals (EEA, 2012). They compete with native amphibians for scarce resources, particularly at the tadpole stage (EEA, 2012) and may reduce biodiversity by preying on a wide range of small mammals (NNSS, undated). Perhaps their biggest impact on native amphibians may be as a vector of the fungus Bactrachocytrium dendrobatidis, which is often fatal to native frogs but is asymptomatic in bullfrogs (EEA, 2012). Tadpoles consume algae and macroinvertebrates (NNSS, 2011). In the Western United States Lithobates catesbeianus is often found in association with another non-native species, the bluegill fish (Lepomis macrochirus), which preys on one of the only predators to eat the bullfrog tadpole, an indigenous dragon-fly nymph (EEA, 2012). The main predators though for tadpoles are adult bullfrogs (Marchant, 2012). In Ireland, herons (Ardea cinerea) may predate adult bullfrogs(Marchant, 2012).
Reproduction
Eggs are laid June to July (NNSS, undated). Females lay 1000 – 40, 000 eggs which hatch in 3-5 days (Snow & Witmer, 2010). Tadpoles metamorphose within 1-2 years (Marchant, 2012).
Pathway and vector description
Has been introduced to some areas of the world, such as Spain and Italy, to be farmed for frog-leg production (Adriaens et al., 2013). The most likely method of introduction to Ireland is either through the pet trade or as a contaminant in fish stocks imported for aquaculture (O'Rourke & O'Flynn, 2014). Once established the species spreads rapidly when conditions are right (NNSS, 2011; O'Rourke & O'Flynn, 2014). Froglets can travel long distances in search of new water, up to 6 miles in a few weeks (Marchant, 2012).
Mechanism of impact
Competition, Predation, Disease transmission
Management approach
There is currently an EU wide ban on the sale of this species and personal and zoo ownership is being phased out (European Commission, 2017).
There is a very high rate of reproduction in favourable conditions and this combined with high numbers, difficulty in detection and lack of effective control methods make eradication difficult (CABI, 2014).
Removal
Various methods are used with some level of success including frogging (rifles, nightlights, electrofishing, rigs, multicapture nets), netting or destruction of eggs (Snow & Witmer, 2010).Double fyke nets (8mm mesh) with a closed empty plastic bottle in the terminal compartment to prevent drowning of adults has shown success also. This method is less labour intensive and allows the return of non-target species to the environment (Louette et al., 2012). Captures are humanely dispatched with an overdose of benzocaine (Louette et al., 2012).
Water draw-down
This method can be effective if timed correctly and a frog proof perimeter is installed (EEA, 2012). Should be carried out between metamorphosis and the start of the breeding season. However, it may have a detrimental effect on non-target species (Adriaens et al., 2013).
Holistic
A combination of removal and habitat restoration such as the reintroduction of native predators e.g. The pike (Esox lucius) may give the best chance of success (Adriaens et al., 2013).
Broad environment
Freshwater
Habitat description
Suited to a wide range of wetland types, particularly those created by human activity e.g. reservoirs, ponds, canals, ditches with plentiful bank-side vegetation but they will colonise any type of permanent still or slow-moving waterbody including lakes, marshes, bogs, rivers and streams. Man's activities therefore may favour the establishment of this species (EEA, 2012).
Species group
Vertebrate
Native region
North America
Similar species
Common frog (Rana temporaria). The common frog has a dark mask behind the eye and the tympanum is smaller or equal in size to the eye. The bullfrog lacks the dorsolateral ridges of the common frog. Bullfrog tadpoles (15cm long) are typically much larger than those of the common frog (4cm long) (NNSS, undated).
Distribution
World distribution(GBIF)
Introduced in western USA and to more than 40 countries internationally (EEA, 2012). In Europe it is established in Belgium, France, Crete (Greece) and Italy but it is also found to be breeding in Germany, the Netherlands and Spain (EEA, 2012).
Native distribution
Eastern North America
Temporal change
Records submitted to Data Centre in 2024
The following map is interactive. If you would prefer to view it full screen then click here.
How can you help
Report any sighting to the National Biodiversity Centre.
Do not purchase or keep as a pet.
Do not release in the wild.
References
Publications
Adriaens, T., Devisscher, S. & Louette, G. (2013). Risk analysis of American bullfrog Lithobates catesbeianus (Shaw). Risk analysis report of non-native organisms in Belgium. Rapporten van het Instituut voor Natuur- en Bosonderzoek 2013 (INBO.R.2013.41). Instituut voor Natuur- en Bosonderzoek, Brussel. https://purews.inbo.be/ws/files/819598/Adriaens_Devisscher_etal_2013_RiskAnalysisNonNativeOrganismsBelgiumAmericanBullfrogLithobatesCatesbeianus.pdf Site accessed 29 September 2017.
CABI. (2014). Rana catesbeiana (American bullfrog) [original text by Marta Stéfani] [Online]. Invasive Species Compendium: Wallingford, UK: CAB International. Available: www.cabi.org/isc Accessed 28 September 2017.
European Commission. (2017). Invasive Alien Species of Union Concern. European Union, Luxembourg.
European Environment Agency (EEA) (2012). The impacts of invasive alien species in Europe. Technical report No 16/2012. EEA, Copenhagen. 114 p. https://www.eea.europa.eu/publications/impacts-of-invasive-alien-species Site accessed 6 October 2017.
Louette, G & Devisscher, S & Adriaens, T (2012) Control of invasive American bullfrog Lithobates catesbeianus in small shallow water bodies. European Journal Wildlife Research (2013) 59:105–114 https://link.springer.com/content/pdf/10.1007%2Fs10344-012-0655-x.pdf Site accessed 29 September 2017.
Marchant, J (2012) American bullfrog, Lithobates catesbeianus. Factsheet. Non-native Species Secretariat (NNSS) http://www.nonnativespecies.org/factsheet/downloadFactsheet.cfm?speciesId=2040 Site accessed 6 October 2017.
Non-native Species Secretariat (NNSS) (2011) Rick assessment for North American Bullfrog – Rana catesbeiana. Risk assessment carried out for Great Britain. http://www.nonnativespecies.org/index.cfm?pageid=143 Site accessed 6 October 2017.
Non-native Species Secretariat (NNSS). (undated). Species Description – North American bullfrog. Identification sheet. http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesId=2040 Site accessed 6 October 2017.
O'Rourke, E & O'Flynn, C (2014) Risk assessment for Lithobates catesbeianus. Risk assessment carried out for Ireland. http://nonnativespecies.ie/wp-content/uploads/2014/03/Lithobates-catesbeianus-American-Bullfrog.pdf Site accessed 6 October 2017.
Snow N.P. & Witmer G. (2010). American Bullfrogs as invasive species: a review of the introduction, subsequent problems, management options,and future directions. Proceedings of the 24th Vertebrate Pest Conference, University of California. https://naldc.nal.usda.gov/download/49725/PDF Site accessed 29 September 2017.
Relevant links
Alien Encounters Species Information
Bullfrog sounds on californiaherps.com
Additional comments
Was previously classified as Rana catesbeiana.
It is regarded by the International Union for Conservation of Nature (IUCN) as one of the world's worst 100 invaders.