Bullfrog (Lithobates catesbeianus)
Description and Morphological Characteristics
The American Bullfrog, the largest species of frog in North America, ranges from 3 ½ to 6 inches in length, with a record length of 8 inches. They have a broad body with skin roughened by fine tubercles. Color varies from olive, to a darker green or brown. Some may have a dark gray or brown reticulate pattern across the back. The belly is pale in color, sometimes with a yellowish tinge, and gray mottling is common. The tympanum in males is noticeably larger than their eyes. They have ridges that run from behind the eye to just below the jaw, curving around the tympanum. They lack dorsolateral ridges, which helps when distinguishing them from the similar looking Bronze Frog. All toes on the hind feet are fully webbed, except the 4th, which extends beyond the webbing.
Range
This species has a wide range, covering the majority of the eastern United States. The range extends from the Atlantic Provinces, south to the southern end of Florida, west to the Rocky Mountains, and south into the northeast corner of Mexico. The natural limits in the western portion of the range are unclear because of the many introductions of the species into western states, even as far as California. American Bullfrogs have also been introduced into Hawaii, other parts of Mexico, Cuba, Puerto Rico, and many other countries across the globe.
Habitat and Feeding
These frogs prefer larger bodies of water than most other species and are found in habitats such as ponds, lakes, bogs, swamps, sluggish portions of streams, and cattle tanks. They are most active during evening and nighttime and tend to stay near the water’s edge, taking shelter in dense vegetation or debris. Bullfrogs prey on any animal that is smaller than their own body size. Smaller bullfrogs primarily feed on invertebrates, but the larger individuals also consume fish, crayfish, smaller frogs, and even mice and small birds. Cannibalism is common within this species.
Breeding and Reproduction
Throughout the native range, breeding occurs from February to October, beginning earlier and ending later in the southern portion of its range. They breed in shallow, permanent bodies of water with ample vegetative cover. Males call while in the water or on land and they become aggressive and territorial during the breeding season. The advertisement call is a low-pitched pulsing drone, resembling the bellow of a cow or bull. Each call lasts approximately one second and they are often repeated multiple times in a row. Females lay eggs in large masses on the surface of the water which eventually drift down into the water and attach to vegetation. They can lay upwards of 20,000 eggs at one time and the length of the larval stage is heavily dependent upon temperature. The larval period is long, lasting as long as 2 years before the tadpole metamorphoses.
Conservation
The American Bullfrog is extremely abundant and common throughout its range. They are not under federal protection but are included on the Texas Parks and Wildlife White List, meaning they can be collected and used for commercial purposes. In some areas, especially where the species has been introduced, populations are so large that efforts to eradicate the species have been put in place. With their ability to quickly colonize new sites and their voracious appetites, introduced bullfrogs are a threat to native species.
Pertinent References
Casper, G. S., Hendricks, R. 2005. American Bullfrog. Pp. 540-546 in M. Lannoo (Ed.), Amphibian Declines: The Conservation Status of United States Species. University of California Press, USA.
Ficetola, G., Thuiller, W., and Miaud, C. 2007. Prediction and validation of the potential global distribution of a problematic alien invasive species: the American bullfrog. Diversity and Distributions 13:476-485.
Ortíz-Serrato, L., Ruiz-Campos, G., and Valdez-Villavicencio, J. H. 2014. Diet of the exotic American bullfrog, Lithobates catesbeianus, in a stream of northwestern Baja California, Mexico. Western North American Naturalist 74:116-122.
Saenz, D., Fitzgerald, L.A., Baum, K.A., and Conner, R.N. 2006. Abiotic Correlates of Anuran Calling Phenology: The Importance of Rain, Temperature, and Season. Herpetological Monographs 20:64-82.
Account Author: Hailey Hester
Photos: James Childress
Edited by Christopher Schalk
The American Bullfrog, the largest species of frog in North America, ranges from 3 ½ to 6 inches in length, with a record length of 8 inches. They have a broad body with skin roughened by fine tubercles. Color varies from olive, to a darker green or brown. Some may have a dark gray or brown reticulate pattern across the back. The belly is pale in color, sometimes with a yellowish tinge, and gray mottling is common. The tympanum in males is noticeably larger than their eyes. They have ridges that run from behind the eye to just below the jaw, curving around the tympanum. They lack dorsolateral ridges, which helps when distinguishing them from the similar looking Bronze Frog. All toes on the hind feet are fully webbed, except the 4th, which extends beyond the webbing.
Range
This species has a wide range, covering the majority of the eastern United States. The range extends from the Atlantic Provinces, south to the southern end of Florida, west to the Rocky Mountains, and south into the northeast corner of Mexico. The natural limits in the western portion of the range are unclear because of the many introductions of the species into western states, even as far as California. American Bullfrogs have also been introduced into Hawaii, other parts of Mexico, Cuba, Puerto Rico, and many other countries across the globe.
Habitat and Feeding
These frogs prefer larger bodies of water than most other species and are found in habitats such as ponds, lakes, bogs, swamps, sluggish portions of streams, and cattle tanks. They are most active during evening and nighttime and tend to stay near the water’s edge, taking shelter in dense vegetation or debris. Bullfrogs prey on any animal that is smaller than their own body size. Smaller bullfrogs primarily feed on invertebrates, but the larger individuals also consume fish, crayfish, smaller frogs, and even mice and small birds. Cannibalism is common within this species.
Breeding and Reproduction
Throughout the native range, breeding occurs from February to October, beginning earlier and ending later in the southern portion of its range. They breed in shallow, permanent bodies of water with ample vegetative cover. Males call while in the water or on land and they become aggressive and territorial during the breeding season. The advertisement call is a low-pitched pulsing drone, resembling the bellow of a cow or bull. Each call lasts approximately one second and they are often repeated multiple times in a row. Females lay eggs in large masses on the surface of the water which eventually drift down into the water and attach to vegetation. They can lay upwards of 20,000 eggs at one time and the length of the larval stage is heavily dependent upon temperature. The larval period is long, lasting as long as 2 years before the tadpole metamorphoses.
Conservation
The American Bullfrog is extremely abundant and common throughout its range. They are not under federal protection but are included on the Texas Parks and Wildlife White List, meaning they can be collected and used for commercial purposes. In some areas, especially where the species has been introduced, populations are so large that efforts to eradicate the species have been put in place. With their ability to quickly colonize new sites and their voracious appetites, introduced bullfrogs are a threat to native species.
Pertinent References
Casper, G. S., Hendricks, R. 2005. American Bullfrog. Pp. 540-546 in M. Lannoo (Ed.), Amphibian Declines: The Conservation Status of United States Species. University of California Press, USA.
Ficetola, G., Thuiller, W., and Miaud, C. 2007. Prediction and validation of the potential global distribution of a problematic alien invasive species: the American bullfrog. Diversity and Distributions 13:476-485.
Ortíz-Serrato, L., Ruiz-Campos, G., and Valdez-Villavicencio, J. H. 2014. Diet of the exotic American bullfrog, Lithobates catesbeianus, in a stream of northwestern Baja California, Mexico. Western North American Naturalist 74:116-122.
Saenz, D., Fitzgerald, L.A., Baum, K.A., and Conner, R.N. 2006. Abiotic Correlates of Anuran Calling Phenology: The Importance of Rain, Temperature, and Season. Herpetological Monographs 20:64-82.
Account Author: Hailey Hester
Photos: James Childress
Edited by Christopher Schalk
