The Differences in a Green Frog & a Bull Frog

The bull frog and green frog belong to the same genus in the ranidae, or true frog family of amphibians. This close relationship means the two species look somewhat alike, but they have a number of differences which help to distinguish them. Both species are common and widespread in their home ranges and are found coexisting in some areas.

  1. Description

    • The main physical difference between bull and green frogs is size, with the bull frog growing up to 8 inches and the green only up to 5 inches. Both frogs are often green in color, but green frogs have a wider variation and can be browner or more yellowish than bullfrogs. The sex in both species can be determined by the ear disc, known as a tympanum, just behind the eyes. In the males of both species this disc is much larger than the eye. In green frog females it is the same size as the eye and in bull frog females it can be smaller.

    Range

    • Green and bull frogs are common to the eastern and central U.S., as far north as southeast Canada and west to Texas and Oklahoma. The bull frog has also managed to establish invasive populations further to the west in California and Colorado. It has also made it into places outside the U.S, including southern Europe, Asia and South America.

    Diet

    • Like all frogs, both species are carnivores and will eat any living thing they can fit into their sizable mouths. Being generally larger, the bull frog can handle larger prey, including smaller green frogs, if given the chance. Insects, small reptiles and other amphibians are the main diet of both frogs. As tadpoles bull frogs mainly feed on aquatic plants, while green frog tadpoles eat algae and small amounts of zooplankton.

    Lifecycle

    • Green frogs breed during late spring and can produce up to two clutches in a season. Bull frogs breed during the warmer summer months and lay only one clutch per season. Bullfrogs produce more eggs per clutch with up to 20,000, while green frogs max out at around 5,000. Green frogs mature more quickly than bull frogs, reaching sexual maturity at around two years, while bull frogs mature at three- to five- years-old. Neither species cares for their eggs once they are laid.

    Vocalizations

    • The two frogs make different noises when they croak, which can help identify the species sight unseen. Bull frogs produce a booming vocalization described as sounding like jug-o-rum. The green frog produces a vocalization like a banjo string being plucked described as a boink or gunk sound.