Lithobates catesbeianus
The American bullfrog is named for its deep call, which sounds like a bull roaring.
Identification
General description: This is the largest frog in Minnesota both as an adult and tadpole. Bullfrogs are distinct from all other true frogs in Minnesota as no dorsolateral fold is present (a dorsolateral fold is a ridge of raised skin running along the length of many frogs’ backs). Adult males have very large tympanic membranes near the eye. Green Frogs and Mink Frogs are native species that are similar in appearance
Snout-vent Length: 3 1/2 - 8 inches (9-20.3 cm). Tadpoles up to 4¾ inches.
Color: Variable with age and temperature – green, brown and mottled skin coloration common. Adult males often have a yellow throat. Belly coloration is white with grey or yellow; brown mottling sometimes also present. Tadpoles are green with scattered black spots and mottling over upper body and tail.
Sounds: A resonant series of deep bass notes sounding like rrr-uum or jug-o-rum.
Reproduction
Bullfrogs begin to breed in wetlands, ponds, and shallow lakes between age two to five. They breed later in the year than many other frogs, typically calling in June into July. A female bullfrog may lay 2,000 to 25,000 eggs in a film on the surface of the water. It takes two to three years for bullfrog tadpoles to develop legs and emerge from the water and two to five additional years to reach maturity.
Food
Bullfrogs eat small mammals, birds, reptiles, fish and even other frogs. They will eat anything that can fit in their mouth.
Predators
Fish, birds and some mammals eat bullfrogs. Some humans hunt them for their tasty legs.
Photo: ©A.B. Sheldon.
Habitat and range
Breeding habitat: Breeding occurs in permanent bodies of water often with thick emergent vegetation. Bullfrogs coexist with other aquatic predators such as large fish.
Summer habitat: This highly aquatic frog prefers permanent bodies of water such as lakes, ponds, sluggish streams, and backwaters of rivers. This species is only native to the southeastern corner of the state though they have been introduced outside of their native range in various areas of the state.
Winter habitat: Aquatic - both adults and tadpoles overwinter underwater.
Population and management
Bullfrogs are native to the southeastern corner of Minnesota. In the past, bullfrogs have been purposefully or accidentally introduced by people to other parts of the state. Since bullfrogs have had negative impacts in other areas where they have been introduced, bullfrogs should not be purposefully moved and introduced to new areas.
Fun facts
The bullfrog provides the majority of the frog legs for gourmet restaurants. While under water, bullfrogs close their nostrils and continue to "breathe" through their skin.
Reporting
Scientists are interested in better understanding bullfrog distribution in Minnesota. If you see a bullfrog in Minnesota (especially in counties besides Houston and Winona Counties), please take photos and submit a report to iNaturalist.
Bullfrog range