Bullfrogs Geographic Range North American bullfrogs (Rana catesbeiana) are only native to the Nearctic region. They are found from Nova Scotia to central Florida , from the East coast to Wisconsin , and across the Great Plains to the Rockies . The natural western limits of this species are now confused due to their introduction into places as far west as California and Mexico . It is known that bullfrogs were introduced to areas of California and Colorado in the early 1900's. The species has also been introduced (accidentally or on purpose) into southern Europe, South America, and Asia Habitat North American bullfrogs must live in water and are therefore usually found near some source of water, such as a lake, pond, river, or bog. Warm, still, shallow waters are preferred. Bullfrogs are becoming increasingly common in areas that have been modified by humans. Increased water temperatures and increased aquatic vegetation, which are common factors of lakes polluted by humans, favor bullfrogs by providing suitable habitats for growth, reproduction, and escape from predators.   Physical Description North American bullfrogs are the largest true frog found in North America , weighing up to 0.5 kg and 203 mm in length. Typical length ranges from 90 to 152 mm. Color varies from brownish to shades of green, often with spots or blotches of a darker color about the back. The hind feet are fully webbed. The sex of an adult bullfrog can be easily determined by examining the size of the tympanum (the external ear of the frog) relative to that of the eye. The tympanum is a round circle located on the side of the head near the eye, and in males it is much larger than the eye. In females the tympanum is as large or smaller than the eye. Also, during the breeding season the throat of the male bullfrog is yellow, whereas the female's is white. Development About four days after fertilization, spotted tadpoles emerge from the floating egg mass. The tadpoles have gills and a tail, which eventually disappears as the tadpole transforms into a froglet. Tadpole development is quite slow; it may take between one to three years to begin transformation from the tadpole stage into the adult stage. Adults reach sexual maturity after an additional two years. Reproduction Breeding takes place in May to July in the north, and from February to October in the south. Fertilization is external, with the females depositing as many as 20,000 eggs in a foamy film in quiet, protected waters. Fertilization is usually, but not always, by one male. Tadpoles emerge about four days after fertilization. These tadpoles may remain in the tadpole stage for almost 3 years before transforming into frogs. Adults reach sexual maturity after 3 to 5 years.   Lifespan/Longevity The average bullfrog lives seven to nine years in the wild. The record lifespan of an animal in captivity is 16 years. Behavior North American bullfrogs prefer warm weather and will hibernate during cold weather. A bullfrog may bury itself in mud and construct a small cave-like structure for the winter. Their hunting style is 'sit and wait.' Bullfrogs can wait for a long time for some type of prey to come by, then, with a flash of the tongue, they grab it and bring it back into their mouths. Bullfrogs are active both during the day and at night; they are most active when the weather is moist and warm. Home Range Adult males are very aggressive and defend their territories, which can range from 3 to 25 meters of shoreline, by physically wrestling with others. Communication and Perception The call of a male bullfrog has a low frequency and can be heard for over one kilometer. The sound is often described as a low rumbling "jug-o-rum". Bullfrogs also have a good sense of vision and sense vibrations.   Conservation Status Bullfrogs do well with changes in the environment that have occured due to human modification, and are becoming increasingly common in areas modified by humans. Bullfrogs have a much higher critical thermal maximum than most other frogs, meaning that they are able to thrive in higher water temperatures. Bullfrogs have a longer breeding season and a higher rate of pre-metamorphic survivorship, which also allows them to be more successful than other frogs. Other Comments Bullfrogs are well known for their enormous legs. They are some of the best jumpers in the world and are used in frog racing in some parts of the United States .