American bullfrog © Joe Crowley
The bullfrog (Lithobates catesbeianus) is the largest frog in North America. The tadpoles of this species are noticeably larger than those of other species.
The bullfrog varies in colour from pale green to dark greenish brown above, is creamy white below and has variable dark mottling on the back or underside. Adult males have pale to bright yellow chins during the breeding season. This species is distinguished by its very large tympani (eardrums), which are always larger than the eyes, especially in males. Bullfrogs have lateral folds but, unlike in other frog species, these folds wrap downward around the tympani rather than trailing down the back. Adult bullfrogs may grow up to 17 centimetres long. The call of this frog is deep and resonant – a vigorous, growling “jug-o-rum.” Listen to the call of the bullfrog (courtesy of Adopt-A-Pond Wetland Conservation Programme).
Green and mink frogs have a dorsolateral fold (a fold of skin running down each side of their back). An adult male green frog also has a large tympanum and yellow breeding colours but is much smaller than an adult male bullfrog.
Bullfrogs, which require large permanent waterbodies to breed but may spend part of the summer in smaller ponds, are usually found in water along a well-vegetated shoreline. Over the winter, bullfrogs hibernate in deep ponds, lakes and rivers.
View an interactive map of the known ranges of American bullfrogs in Ontario.
Bullfrogs breed later than most other frogs, usually from mid-June to late July on warm, humid or rainy nights. The egg masses may contain up to 20,000 eggs and, when first laid, spread out over the surface of the water. Bullfrog tadpoles, which grow for up to three years before changing into frogs, eat suspended matter, organic debris, algae, plant tissue and small aquatic invertebrates.
Male bullfrogs reach maturity about three years after transforming; females may take five or more years to do so. In the wild, bullfrogs are known to live up to nine years after transforming. They are known for their voracious, indiscriminate appetite. They will eat virtually any animal they can swallow, including insects, birds, mammals, reptiles and even other bullfrogs.
Other names: bullfrog, Rana catesbeiana
Threats and Trends
The harvesting of large frogs for food has led to a decline in several species around the world, including the American bullfrog. Frog legs were popular menu items in the 1980s and early 1990s. Harvesting for both food and educational purposes (i.e., dissection) has decimated native bullfrog populations in many wetlands. In Ontario, bullfrogs are returning to some areas where their numbers had been depleted, but whether their overall numbers are increasing is unknown.
Current Status and Protection
Neither the Committee on the Status of Species at Risk in Ontario nor the Committee on the Status of Endangered Wildlife in Canada has assessed the status of the American bullfrog. The species has no protection under the Ontario Fish and Wildlife Conservation Act. The International Union for Conservation of Nature lists the global status of the American bullfrog as Least Concern. The species’ status was confirmed in 2010.
Learn more about reptile and amphibian conservation and what you can do to help these species on our Reptile and Amphibian Stewardship page.