American Bullfrog (Lithobates catesbeianus)
Order Anura, Family Ranidae (True Frogs), Genus Lithobates, Species L. catesbeianus. This species is the largest member of the family Ranidae in North America.
Species
American Bullfrog (Lithobates catesbeianus)
Family
Order Anura, Family Ranidae (True Frogs), Genus Lithobates, Species L. catesbeianus. This species is the largest member of the family Ranidae in North America.
Size
Adult SVL typically ranges from 3.5 to 6 inches (9 to 15 cm), though giants can reach 8 inches (20 cm). Weight ranges from 0.5 to 1.5 lbs. They exhibit sexual dimorphism, with females generally being larger than males.
Conservation
IUCN Status: Least Concern. Populations are stable/increasing. In many areas where they are introduced, they are considered a major threat to native biodiversity due to competition and predation.
Description
An iconic giant of North American wetlands, the American Bullfrog is easily recognized by its size and deep bass voice. The male in the image shows the classic yellow throat and large eardrum of a mature individual, perfectly camouflaged among the shoreline grasses.
Key Features
Large size; no dorsolateral folds on the back; ridge of skin circling the tympanum; large eardrum; yellow throat in breeding males.
Physical Description
A large, robust frog with a broad, flat head. Features include bulging eyes with horizontal pupils and a highly prominent tympanum (eardrum) located just behind the eye. It lacks dorsolateral ridges along the back; instead, a ridge of skin runs from the eye around the tympanum.
Skin Texture & Coloration
Skin is generally smooth but can be somewhat granular. Coloration ranges from olive green to brown with darker mottling. The underside is whitish to yellow. In mature males, the throat often turns a bright, vibrant yellow, as seen in the photograph.
Distinguishing Features
The most definitive field mark is the absence of dorsolateral folds (ridges) extending down the back, combined with a fold that wraps around the large tympanum. In males, the tympanum is significantly larger than the eye, whereas in females, it is roughly the same size.
Habitat
Highly aquatic; found in permanent bodies of water such as lakes, ponds, sluggish rivers, and swamps. They prefer areas with abundant aquatic vegetation for cover and are found from sea level up to moderate elevations.
Geographic Range
Native to eastern North America, from central Florida to southern Quebec. However, they have been widely introduced across the western United States, Europe, Asia, and South America, often becoming invasive.
Behavior
Primarily nocturnal and highly territorial. They use sit-and-wait ambush tactics. When threatened, they often leap into the water with a characteristic 'yip' or splash. They are known to be aggressive predators, occasionally eating other frogs.
Diet & Feeding
Generalist carnivores; they will eat almost anything they can swallow, including insects, crayfish, fish, turtles, snakes, birds, rodents, and other amphibians. They use a powerful, sticky tongue to pull prey into their mouths.
Reproduction
Breeding occurs in late spring and summer. Males congregate in choruses to attract females. Females lay up to 20,000 eggs in large, floating films or mats. Amplexus is axillary (behind the forearms).
Vocalizations
A deep, resonant, baritone 'jug-o-rum' or 'br-wum' that can be heard from a great distance. It sounds somewhat like a low-pitched bellows or a distant lowing cow.
Life Cycle
Eggs hatch in 3 to 5 days. The tadpole stage is exceptionally long, lasting 1 to 3 years depending on climate. After metamorphosis, they reach sexual maturity in 1 to 2 years. Lifespan in the wild is typically 7 to 9 years.
Conservation Status
IUCN Status: Least Concern. Populations are stable/increasing. In many areas where they are introduced, they are considered a major threat to native biodiversity due to competition and predation.
Toxicity & Defense
Not toxic to humans. They rely on size, camouflage, and powerful leaps for defense. Skin secretions may be distasteful to some predators, but they are frequently preyed upon by herons, raccoons, and large fish.
Ecological Role
Functions as an apex predator within the micro-ecosystem of a pond. Historically an 'indicator species' for water quality, though they are more tolerant of pollution than many other amphibians.
Similar Species
Green Frog (Lithobates clamitans), which possesses prominent dorsolateral folds extending at least halfway down the back. Bullfrogs lack these ridges entirely.
Observation Tips
Look for them at the water's edge on warm summer nights using a flashlight. Their eyes reflect a bright gold or silver 'eyeshine.' Listen for the 'jug-o-rum' call near permanent water sources.
Handling & Safety
Handle with wet hands to protect their permeable skin. Be cautious of their powerful kick, which can cause them to slip. They do not pose a toxic risk to humans but may carry salmonella.
Seasonal Activity
Active from spring through autumn. In colder climates, they hibernate (brumate) underwater, buried in the mud at the bottom of ponds where they can survive low oxygen levels.
Cultural Significance
Commonly used in biology classrooms for dissection and laboratory research. Historically a food source (frog legs) in many parts of the world, leading to their global introduction through aquaculture.
Interesting Facts
The Bullfrog is the state amphibian of Missouri, Ohio, and Oklahoma. They are also famous for their role in 'The Celebrated Jumping Frog of Calaveras County' by Mark Twain.