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American Bullfrog (Lithobates catesbeianus)

The American Bullfrog is a prominent amphibian native to North America. During the mating season, which spans from May to July, male bullfrogs are notably vocal, their calls resonating across ponds and lakes. Typically found in shallow waters, bullfrogs are less frequently observed than Green Frog (Lithobates clamitans) but are a fascinating subject for wildlife enthusiasts.

At a Glance – American Bullfrog

How can I tell an American Bullfrog from a Green Frog?

The easiest difference is the dorsolateral fold behind the eye.

• Bullfrog fold: It wraps around the tympanum and stops.
• Green Frog fold: It continues down the back toward the hind legs.
• Extra clue: Bullfrogs are often larger and have a deeper call.

When is the best time to hear or spot American Bullfrogs in Québec?

Late spring to early autumn is best, especially May to July.

• Peak calling: Males are most vocal during the breeding season.
• Best habitat: Search warm, vegetated pond and marsh edges.
• Recorded example: A close-up Québec call recording is available on YouTube Short.
• Field behaviour: They often sit still in shallow water before diving.

Are American Bullfrogs invasive, and why does that matter?

Yes, outside their native range they can become invasive and affect local ecosystems.

• Native range: Eastern and central North America.
• Introduced areas: Western North America plus parts of Europe, Asia, and South America.
• Ecological impact: They can pressure native amphibian communities through competition and predation.

Identification and Similar Species

American Bullfrog is identified by its large body size, broad head, and deep "jug-o-rum" call. Adults are usually olive to brown, often mottled, and typically sit with only the eyes and nostrils above the waterline.

For a local sound reference, see my close-up field recording of an advertisement call: YouTube Short.

The most reliable field mark against Green Frog (Lithobates clamitans) is the dorsolateral fold: in bullfrogs, it wraps around the tympanum and stops; in Green Frogs, it continues down the back.

In breeding season, males often show a yellow throat and a tympanum larger than the eye, while females usually have a paler throat and a smaller tympanum.

Observed Behaviour - Québec (Field Recordings)

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  A close-up view of an American Bullfrog giving a resonant advertisement call at the water surface.

Best Locations and Seasons for Sightings

In southern Québec, American Bullfrogs are most often seen from late spring to early autumn, with calling activity usually strongest between May and July.

Look for them along warm, vegetated edges of ponds, marshes, and quiet lake margins, where they remain still in shallow water before dropping underwater when disturbed.

Around Greater Montréal, I observe them less frequently than Green Frog (Lithobates clamitans), but my most reliable site is Parc Bernard-Landry, with additional regular observations at Lac des Bouleaux in Parc Mont Saint-Bruno.

In my field experience, I almost never spot American Bullfrog (Lithobates catesbeianus) and Green Frog (Lithobates clamitans) in the same place, with Lac des Bouleaux in Parc Mont Saint-Bruno being an exception.

"x" indicates the species was observed, while "-" indicates no observation. Lack of observation doesn't necessarily imply that the species is absent. Data is derived from my park visit journals.

Ecology and Behaviour

Distribution

American Bullfrog is native to eastern and central North America, including southern Canada and much of the eastern to central United States.

It has been widely introduced outside its native range in western North America and across parts of Europe, Asia, and South America, where it can become invasive and affect native amphibian communities.

In Québec, it is associated with warm freshwater wetlands such as ponds, marshes, and slow, vegetated margins of lakes and streams.

Diet

American Bullfrog is an opportunistic carnivorous predator.

• Invertebrates: Beetles, flies, dragonflies, spiders, crustaceans, and other abundant prey.
• Vertebrates: Other frogs, small fish, reptiles, birds, and small mammals when available.
• Diet pattern: Prey use shifts with season, size class, and local availability, contributing to the species' ecological adaptability.

References – American Bullfrog

Most content on this page is based on my direct field observations. General species background (taxonomy, range, and broader ecology) is informed by the sources listed below.

• EOL - Taxonomy and species profile
• Wikipedia - Broad species overview and background
• AmphibiaWeb - Biology, range, and ecology summary
• IUCN Red List - Global conservation status assessment

All content on this page — including photos, videos, and field audio recordings — was created by Karl-Heinz Müller, a Montréal-based wildlife filmmaker, sound recordist, and photographer. Founder of MUUUH and Québec Sauvage, he has spent over a decade documenting Canada’s natural habitats through immersive soundscapes and wildlife films. Learn more about Karl-Heinz

Last updated: 2026-05-28