Wisconsin Sea Grant Frogs: Field Guide

(Rana catesbeiana)

Call: Males give a distinctive, deep "bur-rum"

Size: 9-20 cm in length (3.5-8 inches)

Green, olive, or brown with brownish spots on back and dark bands on upper legs; belly is white or cream-colored. Males have yellow throats, females white throats.

Any still, permanent body of water; bullfrogs are found throughout the Great Lakes region except along northern Lake Superior. They are common in golf course ponds in the upper Midwest.

Confusing Species:
Green Frogs have distinct dorsolateral folds extending at least partway down the back, and their adult size is smaller. The smaller, darker Mink Frog of the far north may lack dorsolateral folds but has rounded spots or lengthwise blotches on the upper surface of the hind legs and a musky, mink-like odor when handled.

Breeding: Mid-May into July

Did you know?

Bullfrogs are the largest frog species in North America, with adults growing up to eight inches long.

The bullfrog tadpole is big too - up to six inches long, including its tail! These tadpoles can take two years to mature into frogs. In fact, large bullfrog tadpoles sometimes can be seen through the ice in frozen ponds in winter.

Male bullfrogs are territorial and defend their home turf by calling out to warn intruders. If that doesn't work, a shoving or wrestling match may follow!

From May to July the male bullfrog's deep "bur-rum" call attracts females, who lay eggs in large, jelly-like masses that can measure a yard across. Smaller males that cannot compete with large males for territories have evolved a trick. They hide out near the large calling male and intercept females attracted to the big male. By this strategy, the small males are able to occasionally mate and pass on their genes.

Bullfrogs are famous for their big appetites. As tadpoles, they eat mostly algae, but adults eat just about anything they can catch and cram in their mouths, including other frogs. Some of the more unusual items on their menu include insects, garter snakes and even ducklings.

Bullfrogs themselves are eaten by birds, turtles, raccoons and snakes. Humans also have developed a taste for bullfrogs -- you might even see bullfrog legs on a restaurant menu.


copyright 2001 University of Wisconsin Sea Grant Institute


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