North American Bull Frog

North American Bull Frog (Eng.), Rana Mugidora Sapo Toro (Sp.), Rana catesbeiana (Sci) Introduced species, Puerto Rico

© Chris Brown, San Diego State University

Information compiled by Alan Mowbray, Interpretive Media Writer, EYNF/LEF

General Information

North American bullfrogs (Rana catesbeiana) are native to the Nearctic region. They are found from Nova Scotia to central Florida, from the East coast to Wisconsin, and across the Great Plains to the Rockies. The natural western limits of this species are now confused due to their introduction into places as far west as California and Mexico. It is known that bullfrogs were introduced to areas of California and Colorado in the mid 1800's. Mark Twain’s famous short story “the Fabulous Jumping Frog of Calevaras County” attests to their existence in the California gold fields of that time. The species has also been introduced into southern Europe, South America, and the Caribbean islands of Cuba and Puerto Rico.

Description

North American bullfrogs are the largest true frog found in North America, weighing up to 17 ounces (0.5 kilograms) and measuring up to 7.9 inches (203 milllimeters) in length. Typical length ranges from 3.5 to 5.9 inches (90 to 152 millimeters). Color varies from brownish to shades of green, often with spots or blotches of a darker color about the back. The hind feet are fully webbed. The sex of an adult bullfrog can be easily determined by examining the size of the tympanum (the external ear of the frog) relative to that of the eye. The tympanum is a round circle located on the side of the head near the eye, and in males it is much larger than the eye. In females the tympanum is as large or smaller than the eye. Also, during the breeding season the throat of the male bullfrog is yellow, whereas the female's is white.

Habits

About four days after fertilization, spotted tadpoles emerge from the floating egg mass. Breeding takes place from February to October. Fertilization is external, with the females depositing as many as 20,000 eggs in a foamy film in quiet, protected waters. Fertilization is usually, but not always, by one male. Tadpoles emerge about four days after fertilization. The tadpoles have gills and a tail, which eventually disappears as the tadpole transforms into a froglet. These tadpoles may remain in the tadpole stage for almost 3 years before transforming into frogs. Adults reach sexual maturity after 3 to 5 years. There is no parental involvement in offspring after the eggs are laid. Newly hatched tadpoles can take care of themselves right away.

Habitat

North American bullfrogs are found near a source of water, such as ponds, rivers or streams. Warm, still, shallow waters are preferred.

Where to look for this animal in the EYNF

This animal is rare in the El Yunque National Forest, but may occasionally be seen in still ponds along the La Mina River nature trail.