The Bullfrog is not a native species in British Columbia. Its natural range lies in the eastern part of North America,
from Canada as far south as Florida. It was introduced to B.C. in theearly part of the twentieth century by people wanting to “farm” it for its meaty legs. It has spread through much of the
Lower Mainland and southern Vancouver Island, and is widely
distributed in the western United States, where several introductions took place.
The Bullfrog is quite distinctive in all its life stages. It is a very large, robust frog, green or brown in colour and with large golden eyes. Adult female Bullfrogs may reach 20 centimetres in length (not including legs!) and 750 grams in weight. Male Bullfrogs are somewhat smaller, as is usual for amphibians. Both sexes have a large and distinct tympanum (“ear”) just behind and below the eye. The tympanum is partly surrounded by a fold of skin that runs from the eye down to the shoulder. Males have a tympanum roughly twice the size of the eye, while females have a smaller tympanum that is about the same size as the eye. There are no dorsolateral folds (the folds of skin that run down the sides of the back of many frogs). The sexes may also be distinguished by their throat colour — adult males have yellow throats, often quite bright, while females have paler cream or white throats. Green Frogs, another introduced species, also have a conspicuous tympanum, but they do have dorsolateral folds. They do not grow as large as Bullfrogs.
Ministry of Environment, Lands and Parks. 2001. Bullfrog (frogwatch factsheet). Ministry of Environment, Lands and Parks. Frogwatch factsheet. 7