American Bullfrog: Size, and Habits Across Continents & More

Native to North America, American bullfrogs (Rana catesbeiana) are found in the Nearctic. They can be found across the Great Plains and the Rockies, from the East Coast to Wisconsin, and from Nova Scotia to central Florida. Due to its introduction into regions as far west as California and Mexico, the species’ natural western limits are now unclear.

It is known that in the middle of the 1800s, American bullfrogs were brought to some parts of Colorado and California. Their existence in the gold fields of California at that time is attested to in Mark Twain’s well-known short story, “the Fabulous Jumping Frog of Calevaras County.” The species has also been brought to the Caribbean islands of Cuba and Puerto Rico, as well as southern Europe and South America.

American Bullfrog Description

The largest genuine frog in North America are the American bullfrogs, which may grow to a maximum length of 7.9 inches (203 millimeters) and weigh up to 17 ounces (0.5 kilograms). The typical length is between 90 and 152 millimeters, or 3.5 and 5.9 inches. Color ranges from brownish to greenish tones, frequently with darker patches or blotches across the back.

The rear feet have full webbed soles. Examining the size of the tympanum, or external ear, in relation to the eye can quickly reveal the sex of an adult American bullfrog. The round circle known as the tympanum is situated on the side of the head next to the eye in men, and it is significantly larger than the eye. In females, the tympanum is either the same size as the eye or smaller. In addition, the male bullfrog’s throat turns yellow during the breeding season whereas the female’s is white.


The spotted tadpoles break free of the floating egg mass around four days after fertilization. February through October is when breeding occurs. The females fertilize externally by laying up to 20,000 eggs in a frothy coating in calm, sheltered waters. Though it’s not always the case, one male fertilizes the egg.

After fertilization, tadpoles appear four days later. Tadpoles are characterized by their gills and tail, which eventually fall off when they become froglets. Before turning into frogs, these tadpoles could stay in the tadpole stage for nearly three years. After three to five years, adults attain sexual maturity. After the eggs are laid, the parents stop being involved with their offspring. Tadpoles that have just hatched may immediately take care of themselves.


Eastern North America is the native home of the American bullfrog. Its native range reaches the Atlantic Coast, Newfoundland in the north, and Oklahoma and Kansas in the west. It is thought to be a threat to the California red-legged frog and to be contributing to the decline of that vulnerable species.

It is extremely common on the West Coast, particularly in California. It has been discovered that American bullfrogs consume the juveniles of the giant garter snake, an indigenous species that is threatened. To urge locals to help limit the expanding population by catching the invasive frogs for food, the Utah Department of Natural Resources started tweeting tips on how to catch and cook American bullfrogs in early 2023.

Other nations and areas where the American bullfrog has been introduced are the Mexican provinces, the Caribbean, Cuba, Jamaica, Italy, the Netherlands, Belgium, and France; these are the western provinces of Canada.

American bullfrogs were brought to these nations for a variety of causes, such as purposeful releases, either as biological control agents or as a source of food; frogs escaped from breeding facilities; and frogs kept as pets either escaped or were released. Because the American bullfrog is comparatively resistant to the fungus that causes chytridiomycosis, scientists are worried that as it expands into new areas, it could help spread the deadly illness by acting as a silent carrier to more vulnerable native frog species.

Life History

American bullfrogs breed in the summertime. Large lakes or ponds are usually where they call from. Around the ponds, males establish territorial boundaries. A territorial male will attack and grapple any other male who attempts to encroach on his territory. In order to communicate with one another, males raise their bodies and show off their brilliant yellow gular sacs, or chins. Ladies don’t show off and have white chins.

Females select males based on the quality of their territories, then lay their eggs in those territories. According to one study, the presence of leeches—which eat the eggs—was a sign of a territory of poor quality. Up to 7,300 eggs can be found in the circular mass of eggs that floats on the water’s surface.

Males who ring are vulnerable to being eaten by plain-bellied and northern diamond-back watersnakes, as well as large eastern snapping turtles. In smaller ponds, young American bullfrogs are frequently seen. 

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