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American Bullfrog - Lithobates catesbeianus
Other Names:  Bullfrog

Aquatic Invasive Species
Non-native Species

Global Rank: G5
State Rank: SNA
(see State Rank Reason below)

Agency Status


External Links

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Copyright by Canadian Amphibian and Reptile Conservation Network
State Rank Reason (see State Rank above)
A conservation status rank is not applicable because this species is not a suitable target for conservation activities as a result of being exotic or introduced.
General Description
Deposited in a thin film, 1-2 eggs thick, containing from 3,000 to 47,840 eggs, and spread out over a large surface area (Howard 1983, McAuliffe 1978 as cited in Bury and Whelan 1985, Maxell et al. 2009). Each ovum is black above, whitish below, and is surrounded by a single jelly layer (Maxell et al. 2009). Ovum diameters are 1.2-1.7 mm (0.05-0.07 in), but, total egg diameters, including the jelly layer, are 6.4-10.4 mm (0.25-0.41 in) (Livezey and Wright 1947).

Tadpoles that have a total length (TL) less than 25 mm (0.98 in) are black with transverse gold bands on the dorsal side of the head and body and with a patch of gold ventrally (Altig 1970, Corkran and Thoms 2006). Larger tadpoles have body and tail musculature that are olive green to yellow base with flecks of yellow and numerous round black dots. Their tail fins are clear to yellow base with flecks of yellow and round dots and flecks of black. The ventral body surface of larger tadpoles is creamy white to bright yellow (Maxell et al. 2009). Larvae have a TL of 3–178 mm (0.12-7.0 in) (Corkran and Thoms 2006, Wright and Wright 1949).

A fold of skin extends from the back of the eye, over the tympanum, down to the front leg. Mature males have tympanums twice the diameter of the eye, while mature females have tympanums about the same diameter as the eye (National Research Council, 1974). Dorsal base color varies based on size. Typically, smaller individuals are pale green to dark olive green with small dark spots, while larger individuals have dark mottling (Maxell et al. 2009). A series of black bands often extends across the legs. Ventral color is cream to bright yellow with gray to dark olive-green mottling usually present (Maxell et al. 2009). As sexual maturity approaches, the upper abdomen in males temporarily turns yellowish in color (Flores-Nava, 2005). Males are also slightly smaller than females and have darkly pigmented thumb pads in contrast to the more delicate streamlined thumb of the female (National Research Council, 1974). Snout-vent length (SVL) of 39-220 mm (1.5-8.7 in) and weighing up to 908 g (32 oz) (Lutterschmidt et al. 1996, Thomas and Wogan 1999, Maxell et al. 2009). American Bullfrogs are not native to Montana.

Males advertise breeding and defend territories with a series of deep, bellowing calls that sound like "brrrruumm" (Werner et al. 2004). Calls can be heard up to 800 meters (2,625 ft) and may be confused with the 'booming' display flight of the Common Nighthawk (Chordeiles minor) (Bryce Maxell, personal observation).

Diagnostic Characteristics
Adults of Northern Leopard Frog (Lithobates pipiens) and Columbia Spotted Frog (Rana luteiventris) have tympanums smaller than their eyes and have white stripes extending from the tip of their snout to their front leg. Both these species lack the fold of skin extending from the back of the eye, over the tympanum, down to the front leg (Maxell et al. 2009).

Northern Leopard Frog and Columbia Spotted Frog lay their eggs soon after snow melt in the spring and their egg masses are round or globular. Larvae of these two species are smaller, do not have a creamy yellow ventral color, and do not have round black dots on their dorsal surface and tail musculature. See sections on distribution to identify possible regions of co-occurrence for American Bullfrog, Columbia Spotted Frog, and Northern Leopard Frog.

Species Range
Montana Range Range Descriptions


Western Hemisphere Range


Range Comments
Native Range: Eastern United States to Minnesota and eastern Colorado south to Texas, but historically absent from the Cape Cod archipelago and associated islands off the east coast (Bury and Whelan 1985, Wiese 1990).

Introduced Range: From Washington, northern Idaho and Montana on the westslope of the Continental Divide in Colorado, New Mexico to Nevada, California and Arizona in the south.

Montana's Bitterroot River and Flathead River basin populations have been established since the 1960's (Black 1969b, 1969a, Werner and Reichel 1994, Reichel 1995b, Hendricks and Reichel 1996b, Werner et al. 1998a, Werner et al. 2004, Maxell et al. 2009), but the Yellowstone River populations have been a later introduction (2000's) with the epicenter being in Billings and expansion downstream (Sepulveda et al. 2015).

Maximum elevation: 1,203 m (3,946 ft) in Flathead County (Werner et al. 2004).

For maps and other distributional information on non-native species see:
Nonindigenous Aquatic Species Database from the U.S. Geological Survey
Invasive Species Habitat Tool (INHABIT) from the U.S. Geological Survey
Invasive Species Compendium from the Centre for Agriculture and Bioscience International (CABI)
EDDMapS Species Information EDDMapS Species Information

Observations in Montana Natural Heritage Program Database
Number of Observations: 642

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Adult and juvenile bullfrogs may migrate overland to find other suitable aquatic habitats, if their existing wetland or pond habitat dries or is undergoing desiccation.

American Bullfrogs are highly aquatic and appear to be mostly limited to warmer permanent water bodies with abundant emergent and/or aquatic vegetation (Giermakowski 1998, Maxell et al. 2009). American Bullfrogs are found in lakes, ponds, cattle tanks, bogs, oxbow wetlands and sluggish portions of streams and rivers. Individuals are rarely found more than a few meters from the edge of the water (Raney 1940, Maxell et al. 2009). So far, they seem to have been unable to invade colder waters and high elevations in Montana, but there is some evidence that they may be adapting to colder water beaver ponds at some localities (Nussbaum et al. 1983, Werner and Plummer 1995b). Adults and larvae overwinter in shallow standing or flowing permanent waters on the bottom’s surface (Stinner et al. 1994). Adults typically do not move more than a few hundred meters within a season and show strong homing abilities when displaced (McAtee 1921, Raney 1940, Durham and Bennett 1963, Currie and Bellis 1969). However, individuals have been known to move up to 2.8 km (1.74 mi) and have been found in temporary pools up to 1.6 km (1 mi) from permanent water (Ingram and Raney 1943, Willis et al. 1956, Hammerson 1999).

Ecological Systems Associated with this Species
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Food Habits
American Bullfrogs are voracious feeders and have been implicated in extirpations of native frogs and turtles and declines in waterfowl production. Tadpoles feed on a variety of algae and bacteria, are commonly coprophagous, and may feed on eggs and smaller tadpoles (Steinwascher 1978b, Ehrlich 1979, Kiesecker and Blaustein 1997b). Because of their herbivorous nature, larvae can have a significant impact upon benthic algae and have the potential to disturb aquatic community structure. Adults will eat anything smaller than themselves, including ducklings, fish, mice, frogs, small turtles, and may frequently cannibalize smaller individuals (Bury and Whelan 1985, Maxell et al. 2009). In Oklahoma, the diet in ponds was predominantly insects such as mostly Coleoptera, Orthoptera, Hemiptera (82% by weight) and crayfish (6% by weight). In streams the diet was mostly crayfish (73% by weight) and insects such as Coleoptera (25% by weight).

Found in lakes, ponds, cattle tanks, bogs, oxbow wetlands and sluggish portions of streams and rivers. American Bullfrogs may be affecting Northern Leopard Frog and Columbia Spotted Frog populations in the Bitterroot Valley. Suitable ponds are now occupied solely by American Bullfrogs. Tadpoles are commonly found with predatory fish because they are apparently not very palatable or nutritious (Lewis et al. 1961, Kirk 1964, Kruse and Francis 1977, Kats et al. 1988). Furthermore, tadpoles release chemicals that have been shown to inhibit reproduction in some fish (Boyd 1975).

Reproductive Characteristics
Breeding takes place in warmer weather from late June through late August. Their loud, deep "jug o'rum" call can be heard from a considerable distance. Females deposit eggs in a thin layer on the surface of warmer waters and can produce 10,000 to 20,000 eggs. (Maxell et al. 2009). Eggs subsequently sink onto submerged vegetation and hatch in three to five days (Bury and Whelan 1985) Tadpoles transform to adults as quickly as 4 months in warmer climates and up to 3 years in colder locations. In colder climates, bullfrogs require year-round persistence of water for tadpoles to mature and over-winter.

In Montana, American Bullfrogs breed during warm weather in late-June and July. Eggs hatch in about 4 or 5 days. The tadpole stage may last 2-3 years in Montana based on Bitterroot and Yellowstone River studies. American Bullfrogs reach sexual maturity in 4 to 5 years. Eggs were observed in western Montana in early July. Tadpoles were observed metamorphosing into juvenile frogs in early June (Maxell et al. 2009).

Current management for the Yellowstone River populations has been to try and eliminate as many populations as possible to prevent further spread. Not much management has taken place in the Bitterroot Valley where bullfrogs have virtually wiped out native amphibians from many of the low valley ponds and wetlands.

Contact information for Aquatic Invasive Species personnel:
Montana Fish, Wildlife, and Parks Aquatic Invasive Species staff
Montana Department of Natural Resources and Conservation's Aquatic Invasive Species Grant Program
Montana Invasive Species Council (MISC)
Upper Columbia Conservation Commission (UC3)

The following was taken from the Status and Conservation section for the American Bullfrog account in Maxell et al. 2009

In Montana the American Bullfrog has been documented with an almost continuous distribution in the valley bottoms along the Bitterroot River downstream of Darby, the Clark Fork River downstream of Missoula, and the Flathead River downstream of Dixon (Hendricks and Reichel 1996b, Werner and Reichel 1996, Werner et al. 1998a). In addition, reproducing populations have been reported in Laurel, Billings and Fort Peck. Individual adults have been reported in Helena, Belgrade, near Silver City northwest of Helena, and near Lake Koocanusa near the Canadian border. The impetus for American Bullfrog introduction in the western United States and in Montana seems largely to be due to their use as a recreational hunting and food item, apparently, in some cases, as a result of native frogs having already declined because of human hunting and consumption (Bury and Whelan 1985, Jennings and Hayes 1985). Unfortunately, American Bullfrogs continue to be introduced into new sites from source populations in and outside of Montana (Bryce Maxell, pers. obs.) even though unauthorized introduction or transplantation of wildlife into the natural environment is prohibited by Montana law (Levell 1995, MCA 87-5-711). American Bullfrogs represent a major predation and competition threat to native amphibians and other vertebrate and invertebrate species. American Bullfrogs have been implicated in the declines of a number of amphibian species throughout the western United States and around the world (Dumas 1966, Black 1969b, Moyle 1973, Hammerson 1982, 1999, Bury and Whelan 1985, Hayes and Jennings 1988, Schwalbe and Rosen 1988, Kupferberg 1994, Lanoo et al. 1994, Arano et al. 1995, Rosen et al. 1995, Stebbins and Cohen 1995, Kupferberg 1997a, Lawler et al. 1999, however, see Hayes and Jennings 1986, and Corn 1994). All 3 life history stages of amphibians may be subject to direct predation by adults of the American Bullfrog (e.g., Korschgen and Baskett 1963, Carpenter and Morrison 1973, Bury and Whelan 1985, Clarkson and DeVos 1986, Werner et al. 1995). Additionally, both the eggs and larvae of native amphibians may be preyed upon by larvae of American Bullfrog (e.g., Ehrlich 1979, Kiesecker and Blaustein 1997b). Furthermore, egg, larval and adult amphibians are also likely to be indirectly affected by the threat of predation due to (1) adult avoidance of oviposition sites where predators are present (e.g., Resetarits and Wilbur 1989), (2) decreased larval foraging as a result of competition or staying in refuges to avoid predators (e.g., Kiesecker 1997, Kiesecker and Blaustein 1998), and (3) decreased adult foraging and growth rates as a result of avoiding areas with American Bullfrogs. Native amphibian larvae or adults may also be subject to chemically mediated interference competition (e.g., Petranka 1989a, Griffiths et al. 1993) or exploitative competition for resources (e.g., Kupferberg 1997a). Finally, native predators such as Gartersnakes (Thamnophis species) that are dependent on larval or adult amphibians as a food source may also be impacted as a result of the loss of native amphibian larvae and the presence of larger American Bullfrog tadpoles and adults that they are unable to efficiently forage on (e.g., Kupferberg 1994). In addition to impacts on native amphibians, American Bullfrogs are known to prey on a variety of invertebrates (Carpenter and Morrison 1973) and vertebrates including young waterfowl, passerine birds, warm and cold water fishes, crayfish, snails, shrews, mice, bats, turtles, muskrat (Ondatra zibethicus), lizards, young alligators, Gartersnakes, Prairie Rattlesnake (Crotalus viridis), and a variety of plant matter (Korschgen and Moyle 1955, Lewis 1962, Korschgen and Baskett 1963, Black 1969b, Tyler and Hoestenbach 1979, Bury and Whelan 1985, Clarkson and DeVos 1986, Schwalbe and Rosen 1988, Stuart 1995, Crayon 1998). The current impact of American Bullfrogs on the native herpetofauna in Montana is not fully known. Black (1969b) reported that bullfrogs seemed to be having a negative impact on Northern Leopard Frog and Columbia Spotted Frog populations in the Bitterroot Valley with the disappearance of some Northern Leopard Frog populations apparently occurring at that time. However, Northern Leopard Frog populations have now been extirpated from virtually all of their former range in western Montana, so it is unlikely that American Bullfrogs were responsible for their declines unless they acted as a vector for disease. Native Long-toed Salamanders (Ambystoma macrodactylum), Columbia Spotted Frogs, Pacific Treefrogs (Pseudacris regilla), Painted Turtles (Chrysemys picta), western Terrestrial Gartersnake (Thamnophis elegans) and Common Gartersnake (Thamnophis sirtalis) appear not to have suffered widespread extirpation as a result of American Bullfrog introduction and many of these species are known to have breeding populations that are syntopic with breeding populations of American Bullfrogs at a few localities were fish have not been introduced in Ravalli and Sanders Counties (Werner and Plummer 1995b, Bryce Maxell, pers. obs.). Corn and Hendricks (1998) found several invertebrates in the stomachs of 21 American Bullfrogs at Lee Metcalf National Wildlife Refuge, and found only one vertebrate, an unidentified fish. Thus, while American Bullfrogs may be responsible for local declines or extirpations from isolated breeding sites, they do not appear to have caused widespread declines of the native amphibians. However, this does not mean that they are currently having no impact or will not cause extirpations of amphibians, invertebrates, or other vertebrates as they become more widespread.

Threats or Limiting Factors
Desiccation or drying of the wetland habitats before tadpoles metamorphose to adults is the limiting factor to bullfrogs. Based on a study in western Washington, conservation of ephemeral wetlands will halt range expansions of bullfrogs. Permanently inundated wetlands and man-made ponds are more likely to house the non-indigenous amphibian.

  • Literature Cited AboveLegend:   View Online Publication
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    • Arano, B., G. Llorente, M. Garcia-Paris, and P. Herrero. 1995. Species translocation menaces Iberian waterfrogs. Conservation Biology 9(1): 196-198.
    • Black, J.H. 1969a. The frog genus Rana in Montana. Northwest Science 43(4): 191-195.
    • Black, J.H. 1969b. Yes--there are bullfrogs in Montana. Montana Outdoors 1969: 4.
    • Boyd, S.H. 1975. Inhibition of fish reproduction by Rana catesbeiana larvae. Physiological Zoology 48: 225-234.
    • Bury, R.B. and J.A. Whelan. 1985. Ecology and management of the bullfrog. U.S. Department of the Interior, Fish and Wildlife Service/Resource Publication 155: 23pp.
    • Carpenter, H.L. and E.O. Morrison. 1973. Feeding behavior of the bullfrog, Rana catesbeiana, in north central Texas. Bios 44: 188-193.
    • Clarkson, R.W. and J.C. DeVos, Jr. 1986. The bullfrog, Rana catesbeiana Shaw, in the lower Colorado River, Arizona, California. Journal of Herpetology 20: 42-49.
    • Corkran, C.C. and C. Thoms. 2006. Amphibians of Oregon, Washington, and British Columbia. 2nd Edition. Vancouver, B.C.: Lone Pine Publishing. 176 p.
    • Corn, J. and P. Hendricks. 1998. Lee Metcalf National Wildlife Refuge bullfrog and painted turtle investigations: 1997. Montana Natural Heritage Program. Helena, MT. 20 pp.
    • Corn, P.S. 1994. What we know and don't know about amphibian declines in the west. p. 59-67. In W. Covington and L. DeBano (tech. coords.), Sustainable ecological systems: implementing an ecological approach to land management. USDA Forest Service, Rocky Mountain Forest and Range Experimental Station, Ft. Collins, Colorado. General Technical Report RM-247.
    • Crayon, J.J. 1998. Rana catesbeiana (bullfrog) diet. Herpetological Review 29(4): 232.
    • Currie, W. and E.D. Bellis. 1969. Home range and movements of the bullfrog, Rana catesbeiana Shaw, in an Ontario pond. Copeia 1969(4): 688-692.
    • Dumas, P.C. 1966. Studies of the Rana species complex in the Pacific Northwest. Copeia 1966(1): 60-74.
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    • Ehrlich, D. 1979. Predation by bullfrog tadpoles (Rana catesbeiana) on eggs and newly hatched larvae of the plains leopard frog (Rana blairi). Bulletin of the Maryland Herpetological Society 15: 25-26.
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    • Giermakowski, J.T. 1998. Microhabitat separation between the bullfrog (Rana catesbeiana) and the Columbia spotted frog (Rana luteiventris) in Western Montana. Undergraduate Thesis, Wildlife Biology Program, University of Montana. Missoula, Montana. 2
    • Griffiths, R.A., J. Denton, and A.L.C. Wong. 1993. The effect of food level on competition in tadpoles: interference mediated protothecan algae? Journal of Animal Ecology 62: 274-279.
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    • Petranka, J.W. 1989a. Chemical interference competition in tadpoles: does it occur outside laboratory Aquaria? Copeia 1989(4): 921-930.
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