American Bullfrog (Lithobates catesbeianus)

Order: Anura; Family: Ranidae (True Frogs); Genus: Lithobates; Species: L. catesbeianus. This family is characterized by smooth, moist skin, large eardrums (tympana), and powerful webbed hind legs designed for swimming and jumping.

Species

Family

Size

The largest frog in North America. Adults typically range from 3.5 to 6 inches (9–15 cm) in Snout-to-Vent Length (SVL), though they can reach up to 8 inches (20 cm). They can weigh over 1 lb (0.5 kg). Females are generally larger than males, showing significant sexual dimorphism.

Conservation

IUCN Status: Least Concern. Populations are stable and expanding in non-native ranges. Major threats include habitat degradation, but they are highly resilient. In many areas, their status as an invasive species is a greater concern than their conservation.

Description

The American Bullfrog is the quintessential 'pond frog' of North America. A heavy-set titan of the shallows, it is easily recognized by its olive-green mask and booming voice that defines summer nights. In the image provided, the juvenile or sub-adult shows the classic lack of dorsolateral folds and the beginning of the characteristic large tympanum, appearing calm but ready for a powerful leap.

Key Features

Absence of dorsolateral folds; prominent tympanum with a fold of skin wrapping around it; large size; robust build; webbed hind feet.

Physical Description

A large, robust frog with a broad, blunt head and large, upwardly tilted eyes. The tympanum (eardrum) is very prominent and located just behind the eye. It possesses powerful, muscular hind limbs with extensive webbing between the toes. Notably, it lacks the dorsolateral ridges (raised skin folds) that run down the back of many other true frogs; instead, a ridge wraps around the tympanum.

Skin Texture & Coloration

Skin is generally smooth but may have small tubercles or a grainy texture, especially in older individuals. Coloration ranges from olive green to brownish-drab dorsally, often with varying degrees of dark mottling or spots. The venter (belly) is typically white or cream-colored, sometimes with greyish mottling. Aposematic coloration is absent; instead, the frog relies on camouflage to blend with aquatic vegetation.

Distinguishing Features

The most diagnostic feature is the absence of dorsolateral folds extending down the back. A distinct ridge runs from the back of the eye, curving down behind the tympanum toward the shoulder. In males, the tympanum is significantly larger than the eye, whereas in females, it is roughly the same size as the eye. The throat of breeding males is often yellow.

Habitat

Highly aquatic; found in permanent bodies of water such as lakes, ponds, sluggish rivers, swamps, and marshes. They prefer areas with abundant aquatic vegetation for cover. While they can tolerate man-made environments like cattle tanks, they require permanent water for their multi-year tadpole stage.

Geographic Range

Native to central and eastern North America, from southern Canada down to the Gulf Coast and west to the Rockies. However, they have been widely introduced to the western United States, Europe, South America, and Asia, where they are often considered a problematic invasive species.

Behavior

Primarily nocturnal but active during the day in warm weather. They are sit-and-wait predators that remain motionless for long periods. They are highly territorial, especially males during the breeding season, and will utilize aggressive physical wrestling. When startled, they often leap into the water while emitting a short 'squeak' or distress cry.

Diet & Feeding

Extremely generalist and voracious carnivores. They eat anything they can swallow, including insects, crayfish, worms, fish, turtles, snakes, birds, bats, and other frogs (including their own species). They use a powerful tongue flip to capture prey.

Reproduction

Breeding occurs in late spring and summer (May–July). Males form loud choruses to attract females. Amplexus is axillary (under the arms). Females lay up to 20,000 eggs in large, floating mass films attached to aquatic vegetation. Parental care is non-existent after egg deposition.

Vocalizations

The distinctive call is a deep, resonant, bass-like 'jug-o-rum' or 'br-wum' that can carry for over half a mile. It is a slow staccato drone. They also produce a sharp, high-pitched scream or 'chirp' when escaping a predator.

Life Cycle

Eggs hatch in 3-5 days. The tadpole stage is exceptionally long, lasting 1 to 3 years depending on climate, during which they can grow up to 6 inches long. Metamorphosis occurs in summer, followed by a juvenile stage that takes 2-3 years to reach sexual maturity. Lifespan is 7-9 years in the wild.

Conservation Status

Toxicity & Defense

Not toxic to humans. Defense mechanisms include excellent camouflage, powerful leaps into deep water, and increasing body size by inflating with air to appear larger to predators. They also secrete a slippery mucus that makes them hard to grasp.

Ecological Role

High-level predators in their native ecosystems that control insect and small vertebrate populations. However, as an invasive species, they outcompete native amphibians and can decimate local biodiversity through predation and the spread of Chytrid fungus.

Similar Species

Green Frog (Lithobates clamitans) is the most common look-alike but possesses prominent dorsolateral folds running down two-thirds of its back. Pig Frogs (L. grylio) have more pointed snouts and different hind foot webbing.

Observation Tips

Visit permanent ponds or lake edges on warm summer nights with a flashlight. Look for the 'eyeshine' (reflection) on the water's surface. They are easiest to find by listening for their low-frequency chorus.

Handling & Safety

Generally safe to handle, but large individuals can bite or scratch with their powerful legs. Always wash hands after handling to avoid Salmonella risk. Ensure hands are wet and free of chemicals (lotion/deet) to protect the frog's permeable skin.

Seasonal Activity

Active from early spring to late autumn. They hibernate (brumate) during winter by burying themselves in the mud at the bottom of ponds or in underground burrows near water.

Cultural Significance

A staple of American folklore and songs (e.g., 'Jeremiah was a bullfrog'). They are frequently used in biology classrooms for dissection to study vertebrate anatomy due to their large size and availability.

Interesting Facts

The bullfrog is the official state amphibian of Missouri, Ohio, and Oklahoma. They are the primary source of 'frog legs' in the culinary world and were intentionally introduced to many countries for farming purposes.

Identified on 7/20/2026