The American Bullfrog (Lithobates catesbeianus) is a large true frog known for its distinctive, deep call, often described as a bellowing “jug-o-rum.” While this amphibian is widespread and familiar in many regions, its native territory contrasts sharply with its current global distribution.
Their Original Home
The American Bullfrog is indigenous to eastern North America, where it thrives across a broad expanse. Its native range primarily encompasses the eastern and central United States, extending west to states such as Idaho and Texas, and north into parts of southeastern Canada, including Nova Scotia, New Brunswick, southern Quebec, and Ontario. Within these areas, the species is commonly found in a variety of aquatic environments.
These habitats include permanent freshwater bodies such as swamps, ponds, and lakes, as well as the slower-moving sections of rivers and marshes. Bullfrogs also readily inhabit human-modified environments, including artificial ponds, canals, and ditches. This adaptability to diverse aquatic settings within its native range has contributed to its success.
Global Spread
The American Bullfrog has become established in numerous non-native regions worldwide. This expansion has occurred on multiple continents, including western North America, South America, Europe, and Asia, with populations found in countries like China, Japan, and South Korea, as well as Hawaii and Puerto Rico. The primary mechanisms driving this widespread distribution are human-mediated.
Intentional introduction for food, particularly for the frog leg trade, and for biological control, is a significant factor. Accidental escapes from aquaculture facilities and the pet trade have contributed to their dispersal. Releasing unwanted pets or tadpoles into natural waterways also facilitates the establishment of new populations.
Consequences of Introduction
The introduction of American Bullfrogs into non-native environments leads to several ecological disruptions. As a voracious, opportunistic predator, the bullfrog consumes a wide variety of native species. Their diet can include insects, fish, other amphibians, reptiles, and even small mammals and birds. This broad diet directly impacts local biodiversity by reducing native populations.
Bullfrogs also outcompete native species for resources like food and habitat. Their large size and rapid reproductive rates, with females laying up to 20,000 eggs at once, give them a competitive advantage over many native amphibian species. They also carry diseases like the amphibian chytrid fungus (Batrachochytrium dendrobatidis) and ranaviruses. While bullfrogs are often resistant to these pathogens, they can transmit them to vulnerable local amphibian populations, causing their decline.