Shapes & sizes of frogs and toads
Minnesota toads and frogs vary greatly in size. Members of the treefrog family, some less than 1 inch long, are more frequently heard than seen. The true frog family includes the largest frog in Minnesota, the bullfrog, which may measure up to 8 inches in length. In general, adult female toads and frogs are larger than males of the same species.
Characteristics useful in identifying toad and frog species:
Tympanum, Dorsolateral fold, Cranial ridge, Paratoid gland.
The presence and size of the tympanum, a round disc that covers the external ear opening, is useful in determining the sex of some species. The tympanum of male Cope's gray treefrogs, gray treefrogs, bullfrogs, green frogs, and mink frogs is larger than the eye of the frog. The females of these species have tympanums equal to the size of their eye. Distinguishing between males and females is easiest during the breeding season, when male toads and frogs have a darker throat color and male toads grow pads on their thumbs.