The largest frog species in the United States, the Bullfrog can reach lengths in excess of 20 cm, however, winter limits the size of specimens found in Minnesota. Often seen at the edges of Lake Sagatagan, this frog has green, rough skin sometimes covered in a brown web pattern on the back and sides. Bullfrog tadpoles can be seen swimming around shallow and weedy areas of the lakes year round. Males are easily distinguished by their oversized eardrum, while females’ eardrums are roughly the same size as their eyes.
The call of the Bullfrog is a loud and deep moan, usually repeated three or more times, sometimes ending with a spit-like “phoot” at the end, which is the male’s territorial call. When calling, the males' inflated vocal sacs can bee seen. As impressive as the loud, baritone breeding call is, both male and female bullfrogs give a high-pitched squeak while jumping into the water when frightened.
The natural range of bullfrogs extends up to the southeast corner of Minnesota, but they are now found in Stearns County due to introduction by humans. In many areas, presence outside of their native range has been disasterous to local aquatic diversity. Release of captive Bullfrogs in this area is strongly discouraged.