The American Bullfrog, Lithobates catesbeianus, is the largest true frog species native to North America. This imposing amphibian is immediately recognizable by its size and its distinctive, deep vocalization that sounds like a bull’s bellowing, which is the source of its common name. The bullfrog’s presence is a defining characteristic of many freshwater ecosystems across its native and introduced range.
Defining Features and Size
The bullfrog’s most noticeable trait is its size, typically measuring between 3.6 and 6 inches (9 to 15.2 cm) in snout-to-vent length, though some individuals can exceed 8 inches (20 cm). Mature frogs can weigh up to 1.1 pounds (0.5 kg). The skin is generally smooth and ranges from olive-green to brownish, sometimes with darker mottling or banding on the back.
A key feature distinguishing the bullfrog is the absence of dorsolateral folds, which are ridges of skin found on many other frog species. Instead, the bullfrog has a fold that extends from above the eye, curving down and around the tympanum, or eardrum. This large, circular tympanum is located behind the eye, and its size indicates the frog’s sex: in males, the tympanum is noticeably larger than the eye, while in females, it is about the same size.
Habitat and Range
The native territory of the American Bullfrog spans Eastern and Central North America, extending from Nova Scotia down to central Florida and westward to the Rocky Mountains. This species prefers permanent aquatic habitats featuring slow-moving or stagnant water. They are commonly found in ponds, lakes, marshes, reservoirs, and sluggish portions of streams.
Bullfrogs require water bodies that persist year-round because their prolonged larval stage cannot survive in temporary pools. Their tolerance for warmer water and modified environments, such as irrigation ditches and man-made ponds, has contributed to their success. Outside of its native range, the bullfrog has been widely introduced, often classified as an invasive species due to its large size and predatory nature.
Diet and Life Cycle
The bullfrog is a nocturnal, opportunistic predator with a broad diet. As a gape-limited predator, it consumes virtually any animal it can fit into its mouth. This includes insects, crayfish, and smaller amphibians, but their diet often extends to small mammals, other frogs, snakes, small birds, and bats.
The life cycle includes a long larval period, especially in colder climates. A female deposits a large, thin, floating mass of up to 20,000 eggs, which hatch in a few days. Tadpoles can remain in the water for several months up to two or three years before undergoing metamorphosis into a juvenile frog. This development allows tadpoles to grow large, sometimes reaching 6 inches (15 cm) in length, aiding their survival.
Males establish and defend territory during the breeding season using their characteristic, low-pitched “jug-o-rum” call. Due to the long larval stage, tadpoles often overwinter in the water, completing transformation after one or more full seasons. Once metamorphosis is complete, the juvenile frog takes an additional two to three years to reach sexual maturity.