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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, 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
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.
Distribution
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 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 their presence.
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