American Bullfrog (Lithobates catesbeianus, formerly Rana catesbeiana)
Order Anura, Family Ranidae (True Frogs), Genus Lithobates. Characterized by smooth skin, long powerful legs, and extensive webbing on the hind feet.
Species
American Bullfrog (Lithobates catesbeianus, formerly Rana catesbeiana)
Family
Order Anura, Family Ranidae (True Frogs), Genus Lithobates. Characterized by smooth skin, long powerful legs, and extensive webbing on the hind feet.
Size
The largest frog in North America. Adults range from 9 to 15 cm (3.5 to 6 in) SVL, but can reach 20 cm (8 in). Weight ranges from 300 to 500 grams, with large specimens exceeding 600 grams. Females are generally larger than males.
Conservation
IUCN Status: Least Concern. Population is stable or increasing. However, they are a major conservation threat in areas where they are introduced, as they outcompete and consume native amphibians.
Description
The American Bullfrog is the quintessential 'giant frog' of the wetlands. Its deep, foghorn-like call is a staple sound of summer nights. Robust and powerful, it is a master of its aquatic domain, blending into lily pads with its green and brown camouflage while awaiting any prey small enough to fit in its cavernous mouth.
Key Features
Large size (over 4 inches), green to brown dorsal color, no dorsolateral folds, skin ridge wrapping around the large tympanum, and fully webbed hind feet.
Physical Description
A very large, robust frog with a broad, flat head. Features a conspicuous circular tympanum (eardrum) behind the eye. It lacks dorsolateral folds (ridges) along the back; instead, a fold of skin wraps around the top and back of the tympanum. Hind legs are long and muscular with fully webbed toes.
Skin Texture & Coloration
Skin is generally smooth but can be slightly granular on the back. Color varies from bright green to olive-drab or brownish with darker mottling. The venter (underside) is typically white or cream, often with grey or yellow mottling. Males often have a bright yellow throat during the breeding season.
Distinguishing Features
The most diagnostic feature is the lack of dorsolateral ridges extending down the back. Instead, the ridge curves tightly around the tympanum. In males, the tympanum is significantly larger than the eye; in females, it is roughly the same size as the eye.
Habitat
Found in permanent bodies of water such as lakes, ponds, sluggish rivers, and marshes. They prefer areas with abundant aquatic vegetation for cover and are rarely found far from the water's edge.
Geographic Range
Native to eastern and central United States and parts of Canada and Mexico. Extensively introduced to the western U.S., Europe, South America, and Asia, where it is often considered a highly invasive species.
Behavior
Primarily nocturnal but often active during the day. Known for sit-and-wait predatory behavior. They are highly territorial; males will physically wrestle other males to defend breeding sites. They jump long distances into water when startled, often emitting a short 'yip' or squeak.
Diet & Feeding
Extremely opportunistic apex predators. They eat almost anything they can swallow, including insects, crustaceans, fish, snakes, turtles, birds, bats, and other frogs (including their own species).
Reproduction
Breeding occurs in late spring to summer. Males call in choruses to attract females. Amplexus is axillary. Females lay massive floating egg masses containing up to 20,000 eggs. No parental care is provided after egg-laying.
Vocalizations
The distinctive advertisement call is a deep, resonant bass 'jug-o-rum' or 'br-wum' that can be heard up to half a mile away. It is slow and repeated at intervals.
Life Cycle
Eggs hatch in 3-5 days. Tadpoles are large, olive-green with black dots, and can take 1 to 3 years to reach metamorphosis depending on the climate. Adults may live 7-10 years in the wild and longer in captivity.
Conservation Status
IUCN Status: Least Concern. Population is stable or increasing. However, they are a major conservation threat in areas where they are introduced, as they outcompete and consume native amphibians.
Toxicity & Defense
Not toxic to humans. Defense mechanisms include camouflage, their large size, and powerful leaps into deep water. They produce mild skin mucus that may be unpalatable to some predators.
Ecological Role
As larvae, they are important grazers of algae; as adults, they are top-tier predators that control insect and small vertebrate populations. In invasive ranges, they cause significant declines in biodiversity.
Similar Species
Green Frog (Lithobates clamitans) is smaller and possesses prominent dorsolateral folds that run two-thirds the length of the back. Pig Frog (Lithobates grylio) has a more pointed snout and more extensive webbing between the fourth and fifth toes.
Observation Tips
Best found on warm, humid summer nights around the edges of ponds using a flashlight. Look for the 'eye shine' reflecting from the water's surface or listen for the deep 'jug-o-rum' call.
Handling & Safety
Safe to handle, but their skin is sensitive. Use wet hands to avoid damaging their protective mucus layer and avoid using lotions/repellents before touching. Larger individuals can deliver a strong kick or a pinch if they bite.
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 absorb oxygen through their skin.
Cultural Significance
A popular cultural symbol of swamps and ponds. Historically and currently used as a food source (frog legs) and frequently used in biology classrooms for dissection and physiological research.
Interesting Facts
The American Bullfrog is the state amphibian of Missouri, Ohio, and Oklahoma. They are famous for 'jumping contests,' most notably Mark Twain’s story 'The Celebrated Jumping Frog of Calaveras County.'