This frog is the largest in North America and is distinguished by lacking dorsolateral folds and having large tympanums, larger than the eye in males. The tips of the fingers and toes are blunt. The webbing is well developed. The skin on the back of this species is rough with random tiny tubercles. There is no dorsolateral fold, but there is a prominent supratympanic fold. The mean snout to vent length for males is 152 mm (range 111-178) and for females it is 162 mm (range 120-183). The males have pigmented nuptial pads. The vocal openings are at the corner of the mouth.
The dorsum is green, with or without a netlike pattern of gray or brown on top. The venter is slightly white, sometimes mottled with gray or yellow. Coloration varies widely depending on the locality of the bullfrog (Conant and Collins 1975).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Canada, Mexico, United States. Introduced: Argentina, Belgium, Brazil, China, Colombia, Cuba, Dominican Republic, Ecuador, France, Germany, Greece, Haiti, Indonesia, Italy, Jamaica, Japan, Malaysia, Peru, Philippines, Puerto Rico, Singapore, Spain, Taiwan, Thailand, Uruguay, Venezuela.
U.S. state distribution from AmphibiaWeb's database: Alaska, Alabama, Arkansas, Arizona, California, Colorado, Connecticut, District of Columbia, Delaware, Florida, Georgia, Hawaii, Iowa, Idaho, Illinois, Indiana, Kansas, Kentucky, Louisiana, Massachusetts, Maryland, Maine, Michigan, Minnesota, Missouri, Mississippi, Montana, North Carolina, Nebraska, New Hampshire, New Jersey, New Mexico, Nevada, New York, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, Vermont, Washington, Wisconsin, West Virginia, Wyoming
Canadian province distribution from AmphibiaWeb's database: British Columbia, Nova Scotia, Ontario, Quebec
R. catesbeiana is widely distributed in eastern North America, ranging from Nova Scotia to central Florida and west to eastern Wyoming, Colorado and New Mexico. It occurs throughout most of Texas and into northwestern Mexico. It has been widely introduced for a variety of purposes, and is now common in many parts of western North America and many other countries, including those in Europe, Asia and South America (e.g., see Lever 2003). Rana catesbeiana is strongly aquatic, and can be found primarily at the edges of lakes, marshes, or cypress bays (Conant and Collins 1975).
Life History, Abundance, Activity, and Special Behaviors
Bullfrogs are often the predominant species in interspecific relationships, contributing to the decline of other amphibians and excluding them from the habitat. Bullfrog juveniles are adept at colonizing new ponds, and they are believed to disperse throughout an environment this way.
Bullfrogs are opportunistic predators, and prey on any animal smaller than themselves. While smaller bullfrogs eat mostly insects, larger bullfrogs consume aquatic species such as fish and crayfish, mice, and other frogs (for a video, see the account on Bufo californicus). Cannibalism is prevalent in a bullfrog's diet, sometimes comprising up to 80% of its food.
The breeding season begins in spring and lasts throughout early summer, but can vary according to latitude. Bullfrogs breed on the surface of shallow, permanent water covered with vegetation. Males make distinctive resonant low-pitched calls with a single note that lasts 0.8 seconds at a frequency of 1.0 kHz. Males also display aggressive territorial behavior in defending good oviposition sites. One clutch consists of up to 20,000 eggs and one quarter of the female's body weight. Duration of the larval stage varies greatly depending on the temperature. Metamorphosis is not synchronized.
For additional details on Life History, please refer to the Lannoo account (click on yellow tab above).
Trends and Threats
Argentina: Introduced populations of R. catesbeiana have been recently reported in San Juan (Sanabria et al. 2005), Misiones (Pereyra et al. 2006), Buenos Aires (Barrasso et al. 2009), and Córdoba and Salta provinces (Akmentins and Cardozo 2009). Most introductions come from intentional or incidental releases from breeding facilities, except for Misiones where the bullfrogs there are believed to be the result of the range expansion of a Brazilian population (Pereyra et al. 2006). The bullfrog's adaptive ability has allowed it to invade a diversity of environments and disperse throughout Argentina. It has been observed to prey on native vertebrates. Although it has not yet been identified as a chytrid carrier in Argentina, its negative influence as a potential disease carrier remains to be further examined. One Argentinian species greatly affected by the presence of R. catesbeiana is Leptodactylus ocellatus, a generalist predator who shares a similar diet with R. catesbeiana and whose larvae are being preyed on by bullfrogs (Barrasso et al. 2009). The increase in number of captive-breeding facilities due to a large demand for human consumption and the lack of effective governmental control thereof are serious concerns in Argentina (Akmentins and Cardozo 2009).
Belgium: Bullfrog larvae have been imported on a large scale for trade in pet shops. Many specimens were released into the wild and were able to survive to reach adulthood (Stumpel 1992). Free-ranging populations of R. catesbeiana have been observed in Belgium (Ficetola et al. 2006). Conservationists are concerned about the potential threat of R. catesbeiana to indigenous species, in particular Rana esculenta, which occupies the same niche (Stumpel 1992).
Brazil: Introductions date as early as the 1930's in association with aquaculture. Except for the coldest months of the year, R. catesbeiana reproduces continuously during warm weather such as that of Brazil (Kaefer et al. 2007). This characteristic is shared with the cane toad (Bufo marinus, another invasive species in Brazil. The degree of native population loss brought on by the introduction of bullfrogs is still being speculated, but the reproductive ability of R. catesbeiana is worrisome. Giovanelli et al. (2008) propose that the Brazilian Atlantic Forest biodiversity hotspot in southern and southeastern Brazil may be the most susceptible to invasion, based on ecological niche modeling. Furthermore, a chytridiomycosis outbreak in an Uruguayan farm with stock that originated from Brazil suggests that Brazilian rearing facilities may contain specimens that are infected by B. dendrobatidis, and could thus be harmful to native anuran species if allowed to escape (Mazzoni et al. 2003). These authors urge the Brazilian government to regulate human introductions of R. catesbeiana more strictly.
China: R. catesbeiana was first introduced to China in 1959. Since then, breeding populations have been established in most provinces of mainland China including Yunnan, Sichuan, Shanxi, and Zhejian Provinces (Wang et al. 2007). The bullfrog has been widely bred for both local consumption and for export since the 1980s (Wu et al. 2005). Escapes occur from rearing pens or in the process of transportation or trade (Wu et al. 2005; Li et al. 2006; Liu and Li 2009). R. catesbeiana poses a great threat to native anuran species due to its voracious feeding habits. Its body size is also much larger than any other native species, and it is known to consume at least 4 of the 10 native species in the Zhoushan archipelago of Zhejian Province. Wang et al. (2007) quantified the predatory impacts of R. catesbeiana and found that body size plays an important role in predator-prey interactions with native anurans of China. It has been suggested that the primary threat posed by juvenile bullfrogs is food competition, whereas the primary threat posed by adult bullfrogs is predation (Wu et al. 2005). Chytridiomycosis has also been reported from introduced bullfrogs (wild, farmed, and market-sold) in Yunnan province, as well as in native amphibians, suggesting that farmed and escaped bullfrogs may present a major threat to native species by carrying disease as well (Bai et al. 2010).
Colombia: R. catesbeiana was introduced into Colombia in the 1990s and inhabits the inter-Andean valleys (Lynch 2006a). The bullfrog was originally introduced in hopes of exploiting it for food consumption, but it is now a biological plague in the valley of the Río Cauca and in certain localities on the western slopes of the Cordillera Oriental in Cundinamarca, as well as the lowlands of the Caribbean Region (Lynch 2006b). Its diet in Colombia has been reported to consist mostly of insects (56%), whereas vertebrates constitute only 2% of the diet (Daza and Castro 1999). Many endogenous Colombian frog species have been impacted by the lethal fungal disease chytridiomycosis; R. catesbeiana is a potential vector in Colombia of the fungal pathogen Batrachochytrium dendrobatidis (Ruiz and Rueda-Almonacid 2008).
Cuba: In the 1920s, both adult and larval bullfrogs were observed in two small ponds near Rincon, a small village approximately 50 kilometers from Havana. It was not deemed a threat to the ecological system in Cuba at that time because it was thought that the bullfrog, which had a larval period of more than one year, would not be able to breed in the many temporary pools in Cuba (Hoffman and Nobel 1927). Now, bullfrogs are present throughout Cuba except the Sierra del Cristal National Park (Fa et al. 2002).
France: Acclimatized R. catesbeiana populations have been recorded in France beginning in the 1960s (Ficetola et al. 2006). It was observed to be occurring near Bordeaux in 1997, in a limited area of gravel pits (Neveu et al. 1997). Currently, southwest France is the European area where the strongest expansion of R. catesbeiana is taking place; it also represents the second largest area in Europe where R. catesbeiana is present, constituting about 2,000 square km. Only three breeding populations have been reported, but observations of isolated individuals suggest that translocations are frequent. These secondary translocations facilitated by humans can substantially increase the rate of population expansion, which may further enhance capture and translocation. A large-scale eradication plan is being carried out in southwest France, including trapping of both adults and tadpoles, and education of local people (Ficetola et al. 2006). Unfortunately, samples of introduced populations of bullfrogs in Loir et Cher are found to be infected with B. dendrobatidis (Garner et al. 2006).
Italy: R. catesbeiana was introduced to Italy in the 1930s, making it the first European country where this species was successfully introduced (Ficetola 2006). It is well established in northern Italy and breeds abundantly. Provinces affected at least since 1960 include Mantova, Pavia, and Verona (Lanza 1962). In northern Italy, the R. catesbeiana population does not appear to have expanded since the 1980's. Some populations are known to be infected by B. dendrobatidis (Ficetola 2006).
Jamaica: Twenty-two R. catesbeiana specimens were first introduced to the Great Morass of the Black River of Jamaica in 1967 for commercial purposes. During the next 4 years it has spread in all directions from the point of introduction and eventually established themselves in the Upper Morass. Although no quantitative population estimates have been conducted, R. catesbeiana appears to have established extensive populations at suitable habitat areas of the island. Its expansion in Jamaica is further facilitated by temperature and lack of competition; the frogs breed continually throughout the year and displace local anurans such as Bufo marinus through habitat competition (Mahon and Aiken 1977).
Japan: R. catesbeiana was first introduced to Japan by a professor at the Imperial University of Tokyo (now Tokyo University) around 1918 (Okada 1927). The frog was already well integrated into the Japanese herpetofauna by 1958-1959, approximately 40 years after its introduction (Telford 1960). R. catesbeiana is firmly established in at least the Kanto and Kansai Plains, the two largest lowland regions of Japan, and many local people recognize it as the "food frog" (Telford 1960). R. catesbeiana resides in freshwater habitats such as rice fields, ponds, and rivers. Studies reveal that it may negatively affect native anuran species such as the endangered Rana porosa brevipoda through predation and food competition. The removal of bullfrogs, along with other invasive exotic species, is highly recommended for conservation of local vertebrates (Hirai 2004). Studies reveal R. catesbeiana populations expanding in paddy fields prefer microhabitat with deep water; managing habitats to reduce immigration of bullfrogs may help prevent the spread of this invasive species (Minowa et al. 2008). A recent die-off of R. catesbeiana from ranavirus lasted from September through October 2008 in a 1000-m2 pond in western Japan. Infected feral populations of R. catesbeiana presents a serious threat to Japanese amphibians (Une et al. 2009). Fortunately, B. dendrobatidis does not seem to have infected introduced populations of R. catesbeiana, and no die-off from chytridiomycosis has been reported (Garner et al. 2006).
Netherlands: bullfrogs were imported for trade in pet shops in the 1980s. Many specimens are released into the wild as larvae or freshly metamorphosed juveniles. In 1991, a reproducing population since 1989 was recorded in a garden pond in the city of Breda (Stumpel 1992). Eradication programs have been carried out in the Netherlands (Scalera 2007).
Puerto Rico: in 1935, the Insular Department of Agriculture and Commerce of Puerto Rico introduced a total of 40 R. catesbeiana specimens from Florida to a specially constructed pond at Rio Piedras. The population expanded successfully, and by 1951 had invaded the neighboring towns of Mayaguez and Humacao. It did not appear to prey on other amphibians, but did consume a diversity of local insects (Perez 1951).
Taiwan: the species was introduced into Taiwan from the United States via Japan in 1924 and 1951 (Hsu et al. 1970). The country actively participates in the production of bullfrog meat, and in fact is the world's top exporter of ranids. However, its native amphibians are at risk of infection by B. dendrobatidis. Taiwan's subtropical climate also creates a suitable environment for the growth of this pathogen (Schloegel et al. 2009).
Uruguay: R. catesbeiana was first introduced in 1987 for farming purposes, but at present most of the farms have closed down. A feral population was reported in 2008 at one of the closed farms at Rincón de Pando. Establishment of the population appears to be at an early stage but is potentially dangerous, as the invaded pond exhibits significant differences from non-invaded ones. For example, R. catesbeiana seems to have some type of positive interaction with fish, because the body size of common fish species are higher in the invaded pond where aquatic vertebrate richness is also highest. Furthermore, R. catesbeiana is the highest fraction of vertebrate biomass, displacing native amphibian species such as Hypsiboas pulchellus. Other negative effects on local amphibian fitness include reducing the premetamorphic period due to competition and predation pressures. The high level of anthropogenic disturbance and large amount of suitable habitat in Uruguay may facilitate R. catesbeiana expansion (Laufer et al. 2008). Recent mass deaths occurred at a large farming facility for bullfrogs 46 km from Montevideo, Uruguay, and the cause is suspected to be chytridiomycosis (Mazzoni et al. 2003). This is potentially dangerous to native anurans if R. catesbeiana were to serve as a carrier of B. dendrobatidis. However, no control program was implemented for these closed farms. Laufer et al. (2008) recommend taking measures against the population expansion as well as searching for new invasion points.
Venezuela: the bullfrog was introduced as a food source around the 1990s, and has established dense populations in 14 natural and artificial ponds as far as 4.3 km away from the point of introduction. Examination of R. catesbeiana specimens in the Venezuelan Andes suggests that the bullfrog acts as a pathogen carrier that causes amphibian population declines in Venezuela (Hanselmann et al. 2004). 79.9% of the bullfrogs surveyed are infected with B. dendrobatidis and carrying an average of 2299 zoospores (Sánchez et al. 2008). Of the infected frogs, 96% appear otherwise healthy, making R. catesbeiana an efficient reservoir host. It is likely that year-round bullfrog breeding will heighten the impact of chytridiomycosis (Hanselmann et al. 2004). Chytridiomycosis is detected in native species occuring in pond, stream and terrestrial habitats from 80–2600 m. Dendropsophus meridensis, an endangered native species sympatric with R. catesbeiana, shows the highest infection prevalence and mean zoospore load (26.7% and 2749 zoospores). Although no clinical signs of disease were detected, environmental stress could potentially increase its vulnerability to the pathogen (Sánchez et al. 2008). B. dendrobatidis is also known to migrate through autoclaved late water to reach distant amphibian populations outside the range of R. catesbeiana dispersal (Hanselmann et al. 2004).
R. catesbeiana has been introduced worldwide, and AmphibiaWeb is in the process of editing the Trends and Threats section of this page for each country.
Introduced populations present great threats to native frogs, due to the bullfrog's voracious feeding habits and the size and competitive ability of the larvae. Although aquatic species and frogs constitute a major portion of its diet, other native species are also likely affected because bullfrogs have been reported to eat snake, birds, and small mammals as well. Furthermore, as bullfrogs are being introduced worldwide, they serve as carriers of the pathogenic fungus Batrachochytrium dendrobatidis (chytrid), which causes the lethal disease chytridiomycosis, believed to be a major factor in recent global amphibian declines (e.g., Garner et al. 2006 found that bullfrogs were consistently chytrid-infected in multiple countries). Infected bullfrogs appear to be rather resistant to chytridiomycosis, whereas the disease is lethal to many other amphibians, making the bullfrog an efficient carrier of the chytrid fungus (Daszak et al. 2004).
Relation to Humans
This large frog is widely farmed for human consumption as a source of meat, as well as for entertainment or as an agent to control pest population (Lever 2003).
The American Bullfrog may hold the key for an antidote for one of the most lethal natural toxins known, saxitoxin, which is produced by cyanobacteria and dinoflagellates and causes shellfish poisoning when there are toxic algal blooms. The frog can resist the toxin with its own protein saxiphilin which binds to saxitoxin and renders it inactive (Yen et al 2019). Understanding how bullfrogs can resist the deadly algal blooms may be important in a warming world where toxic algal blooms become more common.
This species was featured as News of the Week on 5 November 2018:
Invasive species can harm native ecosystems by providing a pathway for pathogen invasion. For amphibians, the most devastating pathogen is the chytridiomycete fungus Batrachochytrium dendrobatidis (Bd). A study by Yap et al. (2018) shows a link between the introduction of the American bullfrog (Rana catesbeiana) and the spread of Bd in western North America. Using museum records, the study found that American Bullfrogs arrived in the same year or prior to Bd in most (83%) western watersheds that had data for both species (n=603 watersheds), suggesting that Bd-GPL in North America may have originated in the eastern US, and bullfrogs may have facilitated Bd invasion in the western US. They show in a suitability model which integrates habitat suitability and host availability, that watersheds with non-native R. catesbeiana in the mountain ranges of the West Coast have the highest disease risk. More studies that use archived specimens from natural history collections are needed to test invasion hypothesis of Bd globally. Read an adaptation of this study as teaching material for high schoolers in Science Journal for Kids (pdf) (Written by Vance Vredenberg)
This species was featured as News of the Week on 6 June 2022:
The global panzootic lineage of the amphibian chytrid fungus (Bd-GPL) has triggered some of the worst disease-related wildlife declines ever documented. However, in some areas of the world, such as the eastern United States, Bd-GPL is widespread but has not caused amphibian die-offs. Byrne et al (2022) revealed a previously unknown association between Bd-GPL lineages and their host species. Specifically, they found that bullfrogs in both their native range (e.g., Pennsylvania) and in their introduced range (e.g., Nevada) carry a specific lineage of Bd-GPL while other amphibians in the same locations are often infected with a different pathogen lineage. This intriguing relationship may be due to a long history of Bd in the eastern US which could have allowed host and pathogen to coevolve. (Written by Allie Byrne)
This species was featured as News of the Week on 5 September 2022:
The American bullfrog (Rana catesbeiana) has become a globally-important invasive species over the last century, wreaking destructive impacts on the ecosystems and economies of places it invades. Though bullfrogs are native to the eastern United States, one of their invasive ranges is the western U.S., where they likely face higher pressure from Batrachochytrium dendrobatidis (Bd), a devastating pathogen of amphibians that they generally tolerate and may be responsible for spreading. LaFond et al (2022) sampled bullfrogs across the U.S. to address an important paradox in invasion biology: species invasions are frequently characterized by strong losses of genetic diversity, yet these species still adapt to diversity of new conditions. They identified the invasion as having originated from one population in the Midwest, with a possibly secondary source in the northwest, and found that the invasive population was characterized by significant losses in mitochondrial genetic diversity. Invader bullfrogs had higher Bd infection prevalence and intensity. However, balancing selection was clearly at work, resulting in invader bullfrogs maintaining diversity at the MHC locus, known to be involved in immunocompetency against Bd in other amphibians. They also found evidence for positive selection on four MHC residues involved in pathogen recognition. Perhaps focusing on adaptive loci, which should better predict evolutionary potential, will help us resolve the genetic paradox of invasion! (Written by Emma Steigerwald)
This species was featured as News of the Week on 26 September 2022:
The global pet trade and transport networks have accelerated the number of introduced amphibian and reptile species worldwide, some becoming invasive problems and have caused extirpation or declines of native species and disruptions of ecosystems. Furthermore, these invasions impact socio-economies (i.e., monetary and social impacts) and human health (i.e., spread of disease). In a first attempt to quantify the financial costs, Soto et al (2022) analyzed the global economic costs caused by invasive alien herpetofauna using a dataset of 21 herpetofauna species, six amphibian and 15 reptile invasive species. They showed the cost of invasive species generally increased over time but peaked between 2011 and 2015 for amphibians and 2006 to 2010 for reptiles. Invasive herpetofauna cost approximately a total of 17.0 billion US$ between 1986 and 2020 and was predominantly associated with the American bullfrog (Rana catesbeiana) and brown tree snake (Boiga irregularis), with 6.0 and 10.3 billion US$ in costs, respectively. Geographically, Oceania and Pacific Islands recorded 63% of total costs, followed by Europe (35%) and North America (2%). The sector most affected by amphibians was authorities-stakeholders through post-invasion species management (> 99%), while for reptiles, impacts were reported mostly through damages to mixed sectors (65%). The results from this study might suggest research biases towards well-known taxa; however, it highlights the importance of synthesizing the cost of herpetofauna invasion to provide a better framework for regulatory policies and investment in control or biosecurity measures (e.g., trade of alien pets). (Written by Umilaela Arifin)
This species was featured as News of the Week on 8 April 2023:
What compounds do amphibians taste? What role might taste play in the biology of amphibians as they develop from larvae to adults? Using comparative genomics, Hao et al. (2023) found unexpected diversity in the Tas2r taste receptors that detect bitter compounds, more than in any other vertebrate group. By looking at the differential expression of the nearly 200 Tas2r genes in the American Bullfrog, they found that tadpoles and adults differently express some genes at high levels. This suggests that variation across development in expression of these bitter receptors is related to the different foods (and presumably different preferences) between herbivorous larvae and insectivorous adults. Interesting areas for further research include how these receptors might be distributed within the mouth, including on the unusual taste “discs” of frog tongues, as well as how closely related species might differ in bitter receptors and thus preferences for different prey. (Written by David Blackburn)
See another account at californiaherps.com.
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Originally submitted by: Christine Lu and Ambika Sopory (first posted 2000-02-14)
Edited by: Kellie Whittaker, Ann T. Chang, Michelle S. Koo (2023-04-09)
Species Account Citation: AmphibiaWeb 2023 Rana catesbeiana: American Bullfrog <https://amphibiaweb.org/species/4999> University of California, Berkeley, CA, USA. Accessed Dec 5, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 5 Dec 2023.
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