American Bullfrog Fact File
The American bullfrog is the largest true frog species found in North America. Their skin is rough with small bumps in random locations and coloured green or brown. This is often marked with spots of brown. On the underside they are white or yellow with some individuals exhibiting dark markings. A large, dark stripe runs down the hind leg. These hind feet are fully webbed. Their eye is golden with a dark coloured, oval shaped pupil which runs horizontally.
Males and females exhibit slight physical differences. The tympanum (the ear drum which is visible as a small disc behind the eye) of the male is larger than female. Males also develop a yellow patch on the skin under their throat in the breeding season.
The larger females measure between 9 and 15cm (3.5 and 6 inches). The largest on record measured 20cm (7.9in). They may weigh as much as 0.9kg (2lbs).
The bullfrog is a carnivore. They feed upon snakes, insects, crustaceans and the eggs of aquatic animals such as fish, insects and salamanders. On a rare occasion they have been observed to eat small bats. In addition to this they are cannibalistic and do not hesitate to eat other frogs and the eggs of frogs.
As a tadpole they are herbivorous and will feed on a range of aquatic plants, insects and the tadpoles of other frogs.
Most of their prey is caught with a sit and wait method. They will relax in one spot and wait for the food to come to them.
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As their name suggests the American bullfrog is native to North America where they can be found across Canada, the USA and Mexico.
They have also been introduced to a number of countries including Argentina, Belgium, Brazil, China, Colombia, Cuba, Dominican Republic, Ecuador, France, Germany, Greece, Indonesia, Italy, Jamaica, Japan, Malaysia, Netherlands, Peru, Philippines, Puerto Rico, Singapore, Spain, Taiwan, Thailand, United Kingdom, Uruguay and Venezuela.
In addition to this they have been introduced to additional parts of the countries to which they are native to. This includes Hawaii and large parts of Mexico.
They were introduced to Costa Rica but have now been removed from this country.
They make their home in wetlands. Their habitat needs to be near water which may be in the form of ponds, swamps, lakes or rivers. They will also make use of man-made habitats such as reservoirs, dams or irrigation ditches. Typically their habitat has abundant vegetation.
Breeding takes place throughout spring and summer.
Males will form a territory at the start of the breeding season. They will prevent other males from entering this area and make a call using the vocal sac which sits under the throat. Females will be attracted to the male whose territory contains the most food.
Following a successful mating the female will deposit thousands of eggs on to the surface of the water in a clump. This clump may contain as many as 20,000 eggs. Prior to laying this can make up as much as a ¼ of their body weight.
The eggs of this species are distasteful and as such there is a low amount of predation by fish.
Their tadpoles may measure up to 15cm (5.9in) long. The tadpole is coloured green or yellow and they have small dark spots across the body.
It may take up to 4 years for metamorphosis in to an adult frog to take place. Frogs which take longer to metamorphose will be larger as adults and as such they are less likely to be eaten by predators.
A single leap can carry the frog between 1 and 2m (3 and 6ft).
In addition to the mating calls of the males females make calls to shown aggression or reciprocation.
While swimming they close off their nostril. They are still able to breed through their skin.
American bull frogs are most active in warm weather. During a period of cool weather they will undertake a hibernation.
Predators and Threats
Introduced populations in the UK made be preyed upon by badgers.
Humans hunt them as a source of frogs legs. This is one of the reasons that they have been introduced in large numbers to other countries. They were also introduced as a means of pest control. In addition they will be captured for use in frog races.
They are a carrier for the chrytid fungus which causes a lethal disease in many frog species. American bull frogs appear to be partly resistant to this and act as an effective carrier. Their spread around the well has greatly increased this problem.
The American bull frog is the largest true frog species to be found in North America.
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