Bullfrogs transplanted out of their native range can create problems
NATURE'S NOTEBOOK
Worldwide there are about 2,700 species of frogs, but only 14 are found in Minnesota. Six are classified as true frogs, five are species of tree frogs and three are types of toads.
Bullfrogs are true frogs. Their deep call sounds like a bull roaring and can be heard on Andy Clay's recordings at www.pca.state.mn.us/sounds/bull.wav .
Bullfrogs measure up to eight inches long and are the largest frog in North America. Their coloration is a greenish-brown with a white to cream colored belly. Males have a yellow throat and females have a white throat. While under water bullfrogs close their nostrils and breathe through their skin.
Bullfrogs are the largest frog in North America and are voracious predators, eating small mammals, birds, reptiles, fish, other frogs and even their own species.
A.B. Sheldon
Bullfrogs breed in wetlands, ponds and shallow lakes between the ages of four and eight. They breed later in the year than other frogs. A female bullfrog lays 2,000 to 25,000 eggs on the surface of the water. It takes two years for bullfrog tadpoles to develop legs and emerge from the water.
Bullfrogs are voracious predators that eat small mammals, birds, reptiles, fish, other frogs and even their own species. In southern states hatchling alligators make up part of their diet. An adult bullfrog eats anything that fits into its mouth, including adult birds.
Fish, birds and some mammals eat bullfrogs. Humans are also a predator as we hunt the large amphibians for their tasty legs. I'm told they taste like chicken, which is what you hear about any exotic wild fare, from turtles to rattlesnakes.
Until recently the native range of the bullfrog in Minnesota was Winona and Houston counties, which border the Mississippi River. In the past, people have tried to introduce bullfrogs to other parts of the state. Backyard ponds, in which people place bullfrogs, have become popular. Some of these bullfrogs escape to the wild after outgrowing the site or due to season's end.
As of 2006, bullfrogs have been found in 18 counties outside their native range. This is a problem for two reasons. According the DNR, bullfrogs often will eliminate other frogs in a body of water. Research has found that introduced bullfrogs often carry a fungus that's deadly to other frog species.
It's illegal to import live frogs without a permit, to take frogs from the wild without a license or to use them for any reason other than as bait.
If you see or hear bullfrogs outside of their native range, call the DNR at (651) 259-5100.
ANDREA LEE LAMBRECHT, naturalist and outdoors photographer, may be reached at andreal@umn.edu.