American Bullfrog (Lithobates catesbeianus)

Order Anura, Family Ranidae, Genus Lithobates, Species Lithobates catesbeianus. True frogs (Ranidae) are characterized by strong, long hind legs for leaping, smooth or slightly rough skin, and webbed feet.

Species

Family

Size

Adults range from 90 to 152 mm (3.5 to 6 inches) in snout-to-vent length, occasionally exceeding 200 mm. Females are typically larger than males. Weight can range from 300 to 500 grams or more, making it North America's largest frog.

Conservation

IUCN Red List status is Least Concern, with a stable or increasing global population due to high adaptability and widespread introductions outside its native range. However, it is considered an invasive species in regions where it has been introduced.

Description

The American Bullfrog is an iconic resident of wetlands, recognized instantly by its deep, resonant call echoing across summer waters. With its stout body, watchful golden eyes, and impressive size, it sits comfortably at the top of the aquatic food web as an opportunistic predator.

Key Features

Absence of dorsolateral folds, very large circular eardrums (tympanum), robust green-to-brown body, and massive adult size.

Physical Description

The American Bullfrog is a large, robust, and stocky frog with a broad, flat head. It has large, prominent eyes with a golden-bronze iris and horizontal pupils, a very distinct circular tympanum (eardrum) behind the eye, powerful hind limbs, and fully webbed toes. It lacks dorsolateral folds (ridges) along its back, which easily distinguishes it from many other ranid frogs.

Skin Texture & Coloration

The skin is relatively smooth to slightly granular, particularly on the back and legs. Coloration ranges from olive-green to dark brown or mottled grey on the dorsal side, often featuring dark spots or blotches. The underbelly is typically white or yellowish, sometimes marbled with grey. Mature males often exhibit a bright yellow or bright green throat during the breeding season.

Distinguishing Features

Key field marks include the complete absence of dorsolateral folds along the back, a very large tympanum (larger than the eye in mature males), and a fold of skin that curves from behind the eye around the tympanum to the foreleg.

Habitat

Inhabits permanent bodies of fresh water, including large ponds, lakes, swamps, and slow-moving streams. Prefers areas with abundant emergent vegetation, warm shallow water, and soft muddy substrates for diving and escaping predators.

Geographic Range

Native to eastern and central North America, ranging from southern Canada down to the Gulf of Mexico and east of the Rocky Mountains. It has been widely introduced across western North America, South America, Europe, Asia, and various islands.

Behavior

Primarily nocturnal and crepuscular, though often active by day. They are solitary and territorial. Locomotion involves powerful leaps or swimming. When threatened, they emit a startled shriek or leap into deep water, diving to the muddy bottom.

Diet & Feeding

Voracious apex predators in aquatic food webs. Diet includes insects, spiders, worms, crayfish, fish, snakes, birds, and small mammals. They use a sit-and-wait ambush strategy, snapping up prey with a sticky tongue and overpowering larger prey with strong jaws.

Reproduction

Breeds from late spring to mid-summer. Males establish territories and emit loud, booming calls to attract females. Females deposit egg masses containing up to 20,000 eggs that float as a surface film on the water. No parental care is provided after egg deposition.

Vocalizations

The advertisement call is a deep, resonant, foghorn-like 'jug-o-rum' or low-pitched drone that can carry over a kilometer across water. Males call chorally from the shallows during warm summer nights.

Life Cycle

Eggs hatch in 3 to 5 days into tadpoles. The larval stage is unusually long, typically lasting one to two years before metamorphosis into froglets. Sexual maturity is reached in 2 to 3 years. Total lifespan can exceed 7 to 10 years in the wild.

Conservation Status

Toxicity & Defense

Non-toxic to humans, though their skin secretions contain mild distasteful compounds that deter some predators. Primary defenses include explosive leaps into water, cryptic camouflage, and sudden loud alarm calls.

Ecological Role

Acts as an apex predator in aquatic ecosystems, controlling insect and vertebrate populations while serving as a food source for wading birds, large fish, and mammals. In introduced regions, they can outcompete native amphibians.

Similar Species

Green Frog (Lithobates clamitans), which possesses prominent dorsolateral folds extending down the back, and Pig Frog (Lithobates grylio), which has a more pointed snout and is restricted to the southeastern United States.

Observation Tips

Best observed at night near the edges of permanent ponds or lakes using a flashlight. Search the shallows where they sit motionless near emergent vegetation or logs.

Handling & Safety

Safe to handle with clean, wet hands, though large individuals can deliver a powerful grip or scratch. Care must be taken not to harm their delicate skin or introduce harmful chemicals from human hands.

Seasonal Activity

Active from spring through autumn. They undergo brumation during the winter months, burying themselves in the mud at the bottom of ponds or streams until water temperatures rise in spring.

Cultural Significance

Frequently featured in folklore, literature (such as Mark Twain's famous short story about the jumping frog of Calaveras County), and popular culture. They are also farmed commercially for frog legs.

Interesting Facts

Bullfrogs are capable of swallowing prey almost as large as themselves, including other frogs, small turtles, and ducklings. Their booming call can be heard from up to a mile away.

Identified on 9/9/2026