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American Bullfrog vs. Green Frog

Look only at the back. A ridge running down it means Green Frog; a smooth back, with the fold curving around the eardrum instead, means Bullfrog. Size decides nothing — a young bullfrog is green-frog-sized, and that is exactly when people get this pair wrong.

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American Bullfrog

Lithobates catesbeianus

Green Frog

Lithobates clamitans
American Bullfrog vs. Green Frog: comparison sheet with the differences marked

Photographs via iNaturalist under Creative Commons licences; the photographers are credited on the sheet.

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