Are There Bullfrogs in Wisconsin?
Yes, bullfrogs are abundant throughout Wisconsin, thriving in lakes, marshes, and wetlands across the state. These large aquatic frogs are most active from spring through fall, and their deep bellowing calls are a signature sound of Wisconsin's wetlands. Learning where to find them and how to identify these impressive amphibians enriches any outdoor experience in the state.
By Tim, founder of Easy Street Markets. I maintain the wildlife database and verify every animal and source myself. Updated August 6, 2026.
Yes, bullfrogs are abundant throughout Wisconsin, thriving in lakes, marshes, and wetlands across the state. These large aquatic frogs are most active from spring through fall, and their deep bellowing calls are a signature sound of Wisconsin's wetlands. Learning where to find them and how to identify these impressive amphibians enriches any outdoor experience in the state.
Where Bullfrogs Are Found in Wisconsin
Bullfrogs are common throughout Wisconsin wherever suitable aquatic habitat exists. They inhabit the edges of lakes and rivers, particularly along Lake Michigan and inland waters including Green Bay and the countless lakes of northern Wisconsin. The Mississippi River backwaters in southwestern Wisconsin provide excellent habitat, and the Fox River system supports strong populations. Central Wisconsin lakes and marshes, including those near the Dells area, harbor abundant bullfrogs. Horicon Marsh, one of the state's most important wetlands, is known for its prolific bullfrog populations. Wisconsin's extensive wetland systems mean bullfrogs live from the agricultural south to the forested north. They prefer areas with emergent vegetation like cattails and lily pads along lake and river margins. Both public wildlife areas and private wetlands support bullfrogs. TheWisconsin wildlife hubprovides detailed information about all wildlife habitats, while thespecific bullfrog guideoffers more targeted local knowledge for finding them.
Season and Timing
Bullfrogs in Wisconsin are most active from April through October, with peak activity in summer months. They emerge from hibernation in spring as water temperatures rise above 50 degrees Fahrenheit. June through August is when their iconic deep bellowing calls are loudest, as males establish territories and attract mates. This mating season is when you are most likely to hear and observe bullfrogs. By fall, their calling diminishes as water temperatures drop. In November, bullfrogs move to deeper water to enter hibernation for the winter. Wisconsin winters are too cold for bullfrogs to remain active, so they spend five to six months in a dormant state at the bottom of lakes and deeper wetlands. Spring emergence depends on water temperature rather than a specific date, so timing varies by location and year. Northern Wisconsin bullfrogs may not fully emerge until late May, while southern areas see activity in April. Understanding these seasonal patterns helps predict when and where to find bullfrogs in Wisconsin. For more seasonal information about Wisconsin's native wildlife, explore theWisconsin wildlife hub.
How to Identify Bullfrogs
Bullfrogs are Wisconsin's largest frog species, reaching up to six inches in body length. They have smooth, shiny skin ranging from green to olive brown, often with darker patterns on the back. Their belly is yellowish or whitish. The tympanum, or ear area, is particularly large and prominent, appearing as a large circular disc behind the eye. Male bullfrogs are larger than females and have a yellow throat. Bullfrogs have powerful hind legs adapted for jumping and swimming, with fully webbed feet. Their call is unmistakable, a deep resonant sound resembling a human voice saying jug-o-rum or onk-onk. Tadpoles are large, greenish, and can reach four inches long, with large eyes positioned on top of the head. When startled, bullfrogs emit a loud croaking alarm call. They differ from smaller Wisconsin frogs in size and bulk alone.
Where Sightings Concentrate in Wisconsin
Bullfrogs concentrate in Wisconsin's most extensive marsh systems and shallow lake habitats. Horicon Marsh in eastern Wisconsin is renowned for massive bullfrog populations visible and audible during summer evenings. The Fox River wetlands support high concentrations of bullfrogs and offer accessible viewing opportunities. Mississippi River backwaters from La Crosse to the southern border harbor dense bullfrog populations, particularly in areas with extensive cattail beds. Door County's lakes and wetlands host abundant bullfrogs, especially in late spring and summer. Northern Wisconsin lakes with shallow, weedy edges provide ideal habitat. Inland lakes with extensive emergent vegetation, such as those in Vilas and Oneida counties, concentrate bullfrogs. Public areas like state wildlife areas and park wetlands offer the best chances for observation. Early evening at dusk is the optimal time to hear and locate them. Summer nights following warm days produce the most intense bullfrog choruses. Visiting these habitats during June or July provides the most rewarding bullfrog experiences in Wisconsin.
Typical Bullfrog Behavior
Bullfrogs are ambush predators that wait motionless for prey to approach. They eat insects, small fish, crayfish, and smaller frogs, striking quickly with their powerful jaws. At night, they rest at the water's edge or on floating vegetation. During the day, they remain mostly submerged, watching for movement. Male bullfrogs are highly territorial and aggressive, defending small areas of marsh or lake edge. Their deep calls serve both to attract mates and warn rival males to stay away. Bullfrogs are excellent swimmers using their powerful legs to pursue prey or escape danger. They spend winter dormant in deep water, emerging in spring to establish territories and breed. Males will cannibalize smaller bullfrogs without hesitation. Bullfrogs are primarily nocturnal hunters but may feed opportunistically during the day. They locate prey using vision, moving only when they detect movement.
Coexistence and Safety Notes
Bullfrogs are native to Wisconsin and fully protected as wildlife. Collecting bullfrogs for any purpose requires a Wisconsin fishing license and compliance with daily take limits set by the Department of Natural Resources. Never collect tadpoles or eggs. Bullfrogs pose no threat to humans. Their deep calls, while loud, are a natural part of Wisconsin's wetland soundscape. Bullfrogs are beneficial predators that control insect and small fish populations. They are an important food source for herons, eagles, otters, and larger fish. In areas where bullfrogs have been introduced outside their native range, they can threaten smaller native frog species through predation. Wisconsin's native frog populations have adapted to coexist with bullfrogs. No special precautions are necessary when encountering bullfrogs in nature. If you want to observe them, approach slowly and quietly during dusk. Respect private property and protected lands when seeking out bullfrogs. Thewildlife resource pagescontain information about all native amphibians.
Common Species People Confuse with Bullfrogs
The green frog is the most commonly confused species with bullfrogs, as both are large and green. However, green frogs are noticeably smaller, rarely exceeding three inches, while bullfrogs reach six inches. Green frogs have a prominent ridge running down each side of the back, which bullfrogs lack. The American bullfrog's call is a deep jug-o-rum, while green frogs produce a twangy ping sound. Pickerel frogs have distinctive square-shaped spots arranged in rows and are smaller than bullfrogs. Their call is a grating trill, completely different from bullfrog bellows. Leopard frogs, found in limited areas of Wisconsin, have round spots and are much smaller. The mink frog is small and produces a clicking call. Spring peepers are tiny frogs with distinctive cross markings and produce high-pitched peeping calls. Gray tree frogs are smaller, bumpy-textured, and gray or brown, not green. True toads like the American toad are warty and terrestrial, not smooth-skinned aquatic frogs. Thewildlife resource pagesprovide comprehensive information about Wisconsin's frog diversity.
Frequently Asked Questions
What do bullfrogs eat? Bullfrogs are carnivorous hunters that eat insects, small fish, crayfish, and smaller frogs. They use a sit-and-wait hunting strategy, lunging at prey when it comes within striking distance. Why do bullfrogs make such loud calls? Male bullfrogs call to establish territories and attract females for breeding. The deeper and louder the call, the more dominant the male. Calling is essential to reproductive success. Are bullfrogs ever found in small ponds? Yes, bullfrogs thrive in ponds, especially larger ones with adequate vegetation and depth. They need at least two to three feet of water for overwintering. Do bullfrogs eat other frogs? Yes, bullfrogs are known for consuming smaller frogs. Large bullfrogs can even cannibalize smaller bullfrogs. This predatory behavior is part of their ecological role in Wisconsin wetlands.
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