Bullfrog: Rana catesbeiana

Common name: Bullfrog
Scientific name: (Lithobates catesbeianus)
Classification name: True Frog

Description: The Bullfrog is the largest frog found in North America. Their tadpoles also grow larger than other species. The colour varies from pale green to dark greenish/brown above and is creamy white below with variable dark mottling on the back or underside. It is distinguished by its very large tympanum which is always larger than the eye, and by the lack of dorsolateral ridges. Adult males have pale to bright yellow chins during the breeding season. Adults may reach up to 17 cm long.

Call The call of the Bullfrog is deep and resonant, often described as a bass, growly “jug-o-rum”. A full chorus can be heard half a kilometre away.

Confusing Species: Subadult Bullfrogs can sometimes be confused with Green Frogs, however Green Frogs have two dorsolateral ridges that run partway down the back. An adult male Green Frog also has a large tympanum and yellow breeding colours, but is much smaller than an adult male Bullfrog.

Distributions: Bullfrogs are native to the deciduous forest zones of Ontario, Quebec, New Brunswick and Nova Scotia. It is introduced to British Columbia where it has spread along the lower mainland and Vancouver Island. It is naturally found through much of the eastern and central United States and has been introduced to numerous locations in the west and well as elsewhere in the world.

Habitat: Bullfrogs require large permanent water bodies to breed but may spend part of the summer in smaller ponds. They are usually found in water along a well vegetated shoreline.

Reproduction: Breeding is later than in most other frogs and usually occurs from mid-June to late July on warm, humid or rainy nights. Egg masses may contain up to 20,000 eggs and spread out over the surface of the water when they are first laid. Tadpoles grow for up to three years before transforming into frogs.

Natural History: Male bullfrogs reach maturity about three years after transforming while females may take five or more years to mature. In the wild, they are known to live up to nine years after transforming. Bullfrogs are known for their voracious appetite and smaller frogs (including other Bullfrogs!) make up an important part of their diet along with insects, small mammals and even occasionally small birds. In winter Bullfrogs hibernate in large, deep ponds, lakes and rivers.

Conservation Concerns: There is a problem with too few Bullfrogs in some parts of their range, such as eastern Ontario, and too many in other parts such as British Columbia where they have been introduced. Many people harvest Bullfrogs for frog’s legs either commercially or for their own use. This is now prohibited in some areas. Harvesting of large frogs for food has lead to a decline in several species around the world and Bullfrogs are no exception. The importance of Bullfrogs for human food has also lead them to be introduced to many areas where they are not native. Because Bullfrogs eat smaller frogs they may contribute to declines in some other species which are not adapted to their presence.