formerly Rana catesbeiana
Bullfrog / Ouaouaron
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, especially in
males, 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 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.
Subadult Bullfrogs can sometimes be confused with
Northern Green Frogs, however Northern Green Frogs have two dorsolateral ridges that
run partway down the back. An adult male Northern Green Frog also has a large tympanum and
yellow breeding colours, but is much smaller than an adult male Bullfrog.
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.
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
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.
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.
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 frogs' legs either commercially or for
their own use. This is now prohibited in some areas. Harvesting of large frogs for
food has led 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