General Adult Description: The American Bullfrog is the largest frog species found in South Dakota and the United States. Adults often measure from 4–6 inches (10–15 cm) in length but may exceed this size. Adult American Bullfrogs are usually an olive green color, with occasional black mottling and bars on the thighs. A small dorsolateral fold starts behind the eyes are curves above and around a large, conspicuous tympanum. Adult males will often be darker than females and can develop a yellow throat during the breeding season. Adult males often have a larger tympanum and enlarged first digits on their forelimbs that are used to help grasp females during amplexus (breeding).
General Larval Description: Tadpoles are usually a greenish or brown color with distinct small black spots. The ventral surface is usually white, with a reticulated patterning of light grayish brown and the eyes on tadpoles are dorsally positioned. Tadpoles can grow to be quite large and are commonly found around 4 inches (10 cm) in length. Larvae are slow to develop (see Reproduction below), but during metamorphosis morphological changes are rapid.
Call Description: Male American Bullfrogs have a very distinctive call. Their breeding call is a series of loud, resonant bass notes often sounding like “rumm… rumm…” or “jug-o-rum”. Additionally, this species often emits an alarm call as it jumps into the water from along the shore that is described as a high pitched squeak.
Behavior: Adult males are territorial and can be aggressive in defending their territory. This species is nocturnal and a generalist predator that consumes a wide range of prey, including invertebrates, snakes, small mammals, and even birds. Unlike most other tadpoles, American Bullfrog tadpoles can secrete toxins from their skin that makes them distasteful, and as such, can be found in habitats where fish are abundant.
Reproduction: This species is considered a late breeder in South Dakota, usually breeding from June to July. Males have a deep call that they utilize especially during mating season. Females lay up to 20,000 eggs on the surface of a body of water and the eggs hatch in four to five days. Tadpoles are slow growing and take multiple years before metamorphosing into terrestrial juveniles.
Habitat: American Bullfrogs are highly aquatic and are restricted to large, permanent bodies of water including large, deep lakes and backwaters of large rivers. Because larvae take multiple years to complete metamorphosis, these habitats cannot freeze solid during the winter.
Species Range: American Bullfrogs are native to the eastern and central regions of the United States. It has been introduced in western states and across the globe often due to commercialization and food trade.
South Dakota Range: The American Bullfrog is restricted to the southern border of the state.
South Dakota Status: This species is not listed by South Dakota Game, Fish and Parks and is managed as a game species and hunted for their meat (hind legs).
Account written by Drew R. Davis and Jacob J. Heumiller