| Species | Rana catesbeiana Shaw, 1802 |
| Family | Ranidae (True Frogs) |
| Status | None |
| State Rank | SE |
| Global Rank | G5 |
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This is a large, heavy-bodied frog with a distinct fold of skin (supratympanic fold) that extends from the eye, around the posterior edge of the external ear (tympanum) to the shoulder. Adults attain sizes up to 150 mm snout-vent length. The dorsal color is tan, brown or olive-brown with varying amounts of black mottling and speckling. Adults typically have some green pigmentation in the area between the upper jaw and eyes. Ventrally the body and legs are white to cream colored with dark mottling. Juveniles resemble adults but have distinct inky black specks on the dorsal surface. Neither adults nor juveniles have dorsolateral folds or an eye mask. Mature males have a tympanum much larger than the size of the eye whereas females have a tympanum similar in size to the eye. Mature males also have a yellow-colored throat and gray swollen pads (nuptial pads) on their thumbs.
Larvae- The tadpole has an oval body with dorsal eyes. The dorsal fin terminates on the body and the tail tip is pointed. Tadpoles less than 25 mm total length are black with gold blotches and relatively short tails. Larger tadpoles are olive green with distinct inky black specks over the dorsal surface. The ventral surface is opaque cream to yellow colored with no metallic pigmentation. Tadpoles may attain a length of 110 mm total length or more before metamorphosis.
Eggs – A female lays thousands (> 6000) of eggs in a thin film at the water surface. The eggs typically cover an area greater than 30 cm in diameter. One gelatinous layer (envelope) surrounds the egg (ovum). The eggs often sink to the bottom before hatching.
Voice –The advertisement call is a loud, deep, bass call that is repeated several times in each series. The call has been described as “jug-o’-rum” and “br-rum.” The species’ common name comes from the fact that the call resembles the roar of a bull heard from a distance. When alarmed, juveniles basking on water edges produce a loud and startling “squeak” as they dive into the water.
See Photos Page.
Frogs - The American Bullfrog, a widespread exotic frog, has a distinct fold (supratympanic fold) from the posterior edge of the eye, around the top of the tympanum and ending at the shoulder. No other native Washington frog or toad has this trait. The American Green Frog (Rana [Lithobates] clamitans) has been introduced to Washington in a few places. The Green Frog has supratympanic folds but is easily distinguished from Bullfrogs by the presence of dorsolateral folds (see key identification photos). This trait is completely absent in Bullfrogs.
The American Bullfrog is North American’s largest frog. Full-sized adults are approximately two times larger than any of Washington’s native True Frogs (ranids) and about a third larger than the non-native American Green Frog.
Larvae- American Bullfrog tadpoles are easy to distinguish from all other native Washington tadpoles. Small tadpoles (less 25 cm total length) are black with gold blotches and short tails. Larger tadpoles are olive green with distinct inky black specks over the entire dorsal surface. The ventral surface is opaque cream-colored or yellow with no metallic pigmentation. American Green Frog tadpoles are similar in general appearance but have dark spots over the dorsal surface instead of inky black flecks and the belly has a coppery sheen.
Eggs – All native Washington frog species have globular egg masses. Our two toad species produce eggs in strings. The non-native American Green Frog is the only species one might encounter in Washington with an egg mass similar to the American Bullfrog. This species is currently documented from only three Washington locations. The overall size of the egg mass is less than 30 cm in diameter and the mass is only one egg layer thick. Three gelatinous layers (envelopes) surround the egg (ovum).
Both American Bullfrog and American Green Frog males produce vocalizations throughout the summer. This habit can be helpful in determining which species is breeding at a site. The Green Frog produces a low-pitched, single-note advertisement call that sounds like a low-note banjo string being plucked “Clung!” This call may be given as a single note or repeated several times in a row.
See Key Features Page.
Bullfrogs are the last anuran to become active and breed in Washington. They are rarely encountered before April and calling does not commence until May or June. Eggs are laid in June and July. In some places, breeding may extend into August. Egg development is rapid. Depending on water temperature and other site factors, time to hatching can be a few days to a week. Tadpoles grow quickly but do not metamorphose until their second or third summer. For transformed frogs, most surface activity ceases in November.
In Washington, American Bullfrogs have been reported from lower elevations in all ecoregions except the Blue Mountains Ecoregion. Most documented sites are in the Puget Trough, Columbia Plateau and Canadian Rocky Mountain ecoregions. See Distribution Map.
For information on the complete range of this species, see NatureServe Explorer.
American Bullfrogs are found in lowland permanent water bodies including wetlands, ponds, lakes, sloughs, creeks and rivers. Although they are primarily a “shore frog” they occasionally move to terrestrial sites at night and they will disperse over land, en mass, on warm rainy nights. Juvenile Bullfrogs have also been observed in road puddles at some distance from aquatic habitat. Puddles and other sources of temporary standing water may be important habitat features for dispersing individuals.
Breeding habitats include a variety of permanent still-water bodies. Bullfrogs are able to exist and breed in water bodies with exotic warm-water fish. Some studies show they may even benefit from the presence of these fishes.
Similar to its native range, Bullfrogs likely overwinter in permanent water bodies near sources of well-oxygenated water. The authors are unaware of any observations of Bullfrogs surface active during the mild winter conditions that exist in lowland western Washington.
Bullfrogs are active both day and night depending on temperature. They are alert, fast frogs that remain motionless until approached closely. When approached, basking Bullfrogs always flee into water and then dive into muck or vegetation. When scooped up in a net, captured individuals often remain completely motionless.
Males hold territories scattered around the edges of permanent water bodies. Males aggressively defend their territories by wrestling invading males out of the territory or under water. Males call sporadically throughout the day. Calling frequency increases at night and males call in synchrony (“chorusing”). Chorusing may also occur during the day at the height of breeding season. Females approach males at their calling stations. Once in amplexus, the pair moves to a different area to lay eggs. Egg development is rapid taking anywhere from a few days to a week depending on water temperatures. Tadpoles grow quickly but do not metamorphose until their second or third summer. The tadpoles can grow to surprisingly large sizes, to 110 mm total length or more, before metamorphosis.
The number of tadpoles and juvenile frogs at a pond, especially in the Columbia Basin, can be astonishing in some locations. Because the tadpoles are unpalatable to fish, they are more visible than most of our native frog tadpoles. Small tadpoles can be observed grazing on submerged portions of lily pads and other vegetation. Large tadpoles are often visible in shallow water on the edges of ponds. They will quickly retreat to vegetation in deeper water if disturbed. Larger tadpoles will also gulp air at the water surface. This behavior is helpful in determining if a pond is occupied but must be used with the knowledge that larger Great Basin Spadefoot tadpoles, larval Tiger Salamanders and some aquatic insects also breach the water surface.
American Bullfrogs are native to the eastern United States. They have been introduced throughout the west since the early part of the 1900s. The Bullfrog is now considered an invasive problematic species in Washington. Current Washington regulations prohibit transport of live Bullfrogs or Bullfrog tadpoles without a Washington Department of Fish and Wildlife permit.
In a newspaper article called “The ‘Bushman’ Frogs” from the Daily Olympian, September 3, 1972, Clara Snyder contends that her sister and brother-in-law, The Bushmans, were the first to introduce Bullfrogs to Thurston County. The Bushmans owned a farm near Offut Lake (then known as Bushman Lake, and also called Tempo Lake) and operated the M & B Bar in Centralia. The story goes that they acquired four pairs of Bullfrogs from Louisiana to put on display as an attraction to get more people to visit the M & B Bar. Other early introductions to Washington, and the West, were primarily for harvest of frog legs. In more recent times, people introduce them because they like to hear the booming call of the males during the summer. Until recently, Bullfrog tadpoles were sold in local nurseries for garden ponds. Even with regulations that limit new human introductions, the species will continue to spread by natural dispersal.
Research efforts involving this species have focused on the impact Bullfrogs have on native species, particularly True Frogs (ranids). The authors are unaware of any Bullfrog natural history research for Washington.
None at this time.
Bullfrogs in their native range are important in structuring amphibian communities. Bullfrogs have been suggested to have negative impacts on native Washington species, especially the Oregon Spotted Frog, Leopard Frog, and Western Pond Turtles. Others have suggested that exotic warm-water fishes may actually be the main culprit in the decline of some native True Frogs (ranid) in the West and/or that Bullfrogs and exotic warm-water fishes interact in a way that results in a negative impact on native amphibians. In addition to predation and competition, there are also concerns that Bullfrogs may be vectors for diseases that can infect native frog populations.
Adams (2000), Adams et al. (2003), Garner et al. (2006), Harding and Holman (1992), Hayes and Jennings 1986, Hallock and Leonard (1997), Hecnar and M’Closkey (1996), Kruse and Francis (1977), Lardie (1963), Leonard et al. (1993), McAllister and Leonard (1997), McAllister et al. (1999), Nussbaum et al. (1983), Pearl et al. (2004), Stebbins (2003), Washington Dept. of Wildlife (1993).
Hallock, L.A. and McAllister, K.R. 2009. American Bullfrog. Washington Herp Atlas. http://www1.dnr.wa.gov/nhp/refdesk/herp/
Last updated: May 2009