North American Bullfrogs
Bullfrogs are the largest real frog found in North America. They grow to an average of to be about 3 1/2 to 6 inches long in body length (although some on record are as large as 8 inches!!), legs add another 7 to 10 inches. Their color varies from brownish to shades of green, often with spots or blotches of a darker color around their backs. Their back feet are fully webbed.
How do you tell the boys bullfrogs from the girl bullfrogs?Well thats easy. When looking at an adult bullfrog examine the size of the external ear of the frog and compare to the size of their eye. The ear 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 ear is as large or smaller than the eye. Also, during the breeding season the throat of the male bullfrog is yellow, and the female's is white.
Where Do American Bullfrogs Live?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.
What kind of habitat do they live in?North American bullfrogs need to live in water and are therefore usually found near some source of water, like a lake, pond, river, or bog. Warm, calm, shallow waters are their favorite places. Bullfrogs are becoming much more common in areas that have been changed by humans. Increased water temperatures and increased amounts of water plants, which are common signs of lakes that have been polluted by humans, favor bullfrogs by providing good habitats for growth, having tadpoles, and escaping from predators.
How do they grow?It takes about 4 days for spotted tadpoles to 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 full maturity and are able to have tadpoles after an additional two years.
How long do bullfrogs live?The average bullfrog lives seven to nine years in the wild. The record lifespan of an animal in captivity is 16 years.
How do Bullfrogs behave?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. Adult males are very aggressive and defend their territories, by physically wrestling with others.
How do they communicate with eachother?The call of a male bullfrog has a low frequency and can be heard for over a distance. The sound is often described as a low rumbling "jug-o-rum". Bullfrogs also have a good sense of vision and sense vibrations. See a video of a bullfrog calling here: http://www.midwestfrogs.com.
What do Bullfrogs eat?Bullfrogs are predators. They usually eat snakes, worms, insects, crustaceans, frogs, tadpoles, and aquatic eggs of fish, frogs, insects, or salamanders. They are cannibalistic and will not hesitate to eat their own kind. There have also been a few cases reported of bullfrogs eating bats. Bullfrog tadpoles mostly graze on aquatic plants.
What eats Bullfrogs, and how do they avoid being eaten?Humans hunt bullfrogs for frog legs, but they have a limited hunting season in most states. Bullfrogs are also eaten by a wide variety of other animals, depending on the region. These include herons, turtles, water snakes, raccoons, and belted kingfishers. Most fish are averse to eating bullfrog tadpoles because of their undesirable taste.
Do they cause problems?Introduced bullfrogs may be driving native frogs to extinction in some areas. Colorado, among many other places, is experiencing problems due to the introduced bullfrog population. Bullfrogs may have been introduced accidentally to trout streams and lakes during the Colorado Divisions of Wildlife fish stocking operations. Bullfrogs occasionally invade fish hatchery ponds and their larvae are caught along with the fishes that are routinely stocked in ponds.
How do they interact with us?North American bullfrogs help to control insect pests. They are important for medical research because their skeletal, muscle, digestive, and nervous systems are similar to those of other animals. They are often hunted for meat (frog legs).
Are they endangered?Bullfrogs are dealing fairly well with the changes in the environment that have occurred due to human influences, and they are becoming increasingly common in areas that have been 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 high rate of surviving through the tadpole stage, which allows them to be more successful than other frogs. In many areas, such as California and Colorado, bullfrogs are driving other frog populations to extinction. An interesting reason to explain why bullfrogs in California might have an advantage over other species that are native to that state is that bullfrogs evolved with many different kinds of fish in eastern North America. For many years in California people have been introducing new fish species that are predators of frogs. Bullfrogs have evolved ways to avoid being eaten by fish, such as tadpoles that are not active much of the time which reduces their exposure to predators. Native frog species of California are also suffering a decline because bullfrogs are intense predators on frog populations.