Most folks find it difficult to like the cold-blooded members of the natural world, but frogs are an exception to that rule. Frogs (and their cousins, the toads) have endeared themselves to people who would never touch a snake or give a lizard a second glance. From fairy tales to lawn ornaments to stuffed toys, frogs are ever-present, loved by almost one and all. Perhaps the best-known frog species in North America is the American Bullfrog (Rana catesbeiana). Bullfrogs are pursued by children as pets and adults as food. They are the source of legends and folk tales, and they play an important role (not always positive) in their environment.
One of the most notable things about bullfrogs is their size. They are the largest frog in North America. Adults vary in size depending on where they live, but they can reach more than 8 inches long and weigh several pounds.
Bullfrog color runs from green to brown, usually with numerous dark splotches on the back. The throat of adult males is yellowish, and the belly is yellow or white. The exposed eardrums, or tympanums, are very large in bullfrogs. In males, the tympanums are larger than the eyes, while in females they are about the same size as the eyes. The eyes of adults are gold in color, and a distinct fold of skin extends from the eye around the ear. The front toes of adults lack webbing, while the toes of the hind feet are fully webbed.
Juvenile bullfrogs (actually all juvenile frogs and toads) are called tadpoles. Tadpoles have gills instead of lungs and are restricted to aquatic environments. As they mature, they develop legs and lungs, and lose their tails. The tadpoles of bullfrogs are also quite large, reaching up to as long as 6 inches before transforming into adults. Bullfrog tadpoles are dark green with black dots, orange eyes and yellow bellies.
Frogs and toads are very vocal animals, and each species has its own distinctive call, especially during mating season. The mating call of male bullfrogs is a deep “jug-a-rum” that can be heard up to a half mile away. When startled, both male and female bullfrogs emit a squeaking sound just before jumping into the water to escape.
Home on the range
Bullfrogs will live in just about any permanent body of fresh water with sufficient food and cover. They are generally found in farm ponds, lakes, marshes, and slow moving streams and rivers. Bullfrogs like areas with abundant vegetation, such as reeds, cattails, water lilies and floating mats of algae, both along the water’s edge and in the water itself.
When it comes to prey, bullfrogs are not picky. They will eat just about anything they are capable of swallowing. While most of their prey consists of insects and other invertebrates, bullfrogs have been known to eat small birds and mammals, snakes, and juvenile turtles. They also frequently feed on other frogs, including other bullfrogs. Bullfrogs have a sticky tongue that is hinged in front (ours is hinged in the back) that they can flip forward and catch prey, especially unwary insects. A bullfrog can also lunge at its prey, especially larger specimens, seize the hapless victim in its powerful jaws and push it down its throat with its front legs. Bullfrog tadpoles are mostly herbivorous, feeding on algae and small bits of aquatic plants, but they have been known to eat eggs and even newly hatched tadpoles.
Both adult bullfrogs and their tadpoles are in turn eaten by a wide variety of other animals (including humans), such as wading birds like herons and egrets, otters, mink, turtles, fish, snakes and alligators. Oh yeah, and other bullfrogs.
Froggie goes a courting
Male bullfrogs are highly territorial and let other males know where their territory is by croaking. This also sends a signal to females. Males try to mate with as many females as will enter their territory.
An interested female will enter the male frog’s territory to deposit up to 20,000 eggs at one time. The eggs are placed in shallow water (only a few inches deep) in large masses held together by a gelatinous material. The male bullfrog fertilizes the eggs externally by mounting the female frog, holding onto her with his front legs (this is called amplexus) and releasing his sperm onto the egg mass as it is deposited. It may take up to two years for bullfrogs to fully develop from an egg to an adult.
Both adult frogs and tadpoles hibernate during the winter by burying themselves in the mud or digging underwater burrows. During this time, their metabolism is reduced to almost nothing, although they continue to breathe through their moist skin in a state of suspended animation. When the water temperature warms up, they emerge and become active again.
A slimy plague
While bullfrogs are native to the eastern United States and southeastern Canada, they have been introduced to many western areas. As early as the 1890s, bullfrogs were introduced to the West Coast of the United States to provide a ready source of frog legs. Today, bullfrogs are found from Arizona and southern California to British Columbia and in many western states, including Hawaii. American bullfrogs have also been introduced to other parts of the world, such as Latin America, the Caribbean and Southeast Asia.
While many amphibian species around the world have declined, bullfrogs have thrived and are one of the few species of amphibians conservationists have little fear will ever go extinct. As a matter of fact, wildlife specialists from many areas outside the bullfrog’s native range are concerned about their apparent success in these new areas.
These new-to-the-bullfrog environments may lack bullfrog predators, resulting in exploding populations. The increased competition from introduced bullfrogs has decimated populations of some species, such as the red-legged frog, tree frog and leopard frog found throughout much of the western United States. Adult bullfrogs both feed on the native species and crowd them out of their habitats.
If American bullfrogs are not native to your location, do not introduce them to ponds, streams or other water bodies on your properties. This can be detrimental to many other species and may even be illegal. If you are not sure about the status of bullfrogs or hunting restrictions in your area, check with your state wildlife conservation agency.
In some areas outside their native range, the introduction of bullfrogs has turned this fascinating creature into just another pest. We can try to correct this situation by controlling bullfrogs wherever possible. Likewise, wherever bullfrogs occur naturally, we need to make sure they continue to be an integral part of an aquatic environment that can be enjoyed by all; whether you’re listenin’, lookin’ or giggin’.
John Marshall teaches in North Little Rock, Arkansas, commuting from the small town of Benton, where he lives with his wife, children, granddaughter and several pets.