While hiking the other day, we saw the frog pictured below. The night before, the temperature had dropped to below freezing. Yet this critter seemed happy and active. Frogs never fail to surprise me.
At first glance, this looks like a young bullfrog (a very common frog in the midwest US). But this is actually a green frog (Lithobates clamitans). The bullfrog grows much larger, but a younger one looks a lot like a green frog.
How can you tell the difference? See that fold of skin extending from the frog's eye all the way down the length of its body? That's a sure sign this is a green frog. Bullfrogs only have the fold that wraps around the tympanum (the circular structure behind the frog's eye that serves as an eardrum).
By the way, the tympanum also allows you to determine if the frog is male or female. In this photo, see how the tympanum is much larger than the frog's eye? This means it's a male. If the tympanum is equal to or smaller than the eye, it's a female. This is true for green frogs and bullfrogs.
Green frog - Stan C. Smith
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