American Bullfrog vs. Green Frog

American Bullfrog (Lithobates catesbeianus)

Green Frog (Lithobates clamitans)

Though most experts consider these "elementary" herp ID, this duo of frogs has been tricky for new herpers and naturalists for years. While some aspects are easy, others are less simple. The two can have very similar patterns, and yes... Most Green Frogs are not green... Maybe "Green-lipped Frog" would have been a better name.

But I digress... Anyways, the truth is the two are quite easy for the trained eye to ID, and other than a few rare instances they should not be tricky for anyone. Both species are statewide, and very common. So, here are 6 simple ways to distinguish the two species (other than by call). 

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1. Green Frogs have a clear, distinct dorsolateral ridge a.k.a. coastal fold. Bullfrogs loose this fold during metamorphosis, usually as their tail reabsorbs. Only on old male Green Frogs may this ridge break-up, but they usually retain a line of "warts". 

2. Bullfrogs have huge, wide heads, while Greens have smaller pointer heads. Looking down on the two, one will notice the Green Frog has a very "V"-shaped head while Bullfrog heads are more of a pointed "U".

3. Adult Green Frogs usually have a clear ridge-line from the nostril to the "eye brow", while Bullfrogs have very smooth, domed snouts. Bullfrogs also have a wider gap between their eye and jawline. 

4. Size can sometimes be used as full-grown Bullfrogs are MASSIVE. Adult Bullfrogs will eat adult Green Frogs... Happily... If you are looing at a frog well over 4 inches snout-to-vent, and/or thicker than a soda can, you can bet your bottom dollar it is a Bullfrog.

Adult male American Bullfrog with the hind toes of a full-grown, adult Southern Leopard Frog extruding from its mouth.

​5. The webbing on the hind feet of an American Bullfrog is far more extensive than that of the Green Frog. Often it is difficult to see the webbing on a Green frog's hind foot when sitting, while that is not the normal case for the Bullfrog. In the hand, they are totally night-and-day different (as seen below).

6. If your specimen is a tadpole, Bullfrog Tadpoles are usually a tan or greenish-gold in color, with tiny, black "pin-pricks". Greens are usually a gray or dark brown with black mottling. Bulls do not have any black pattern on the lower half of their tail, while Greens do. When transitioning, Bullfrog tadpoles can have dorsolateral ridges. 

Metamorph American Bullfrog

Metamorph Green Frog

Male Green Frog (left) and a female Green Frog (right). Both Green Frogs and Bullfrogs can be sexed as adults based on how large their tympanums are. Generally, if the tympanum is about equal to the size of the eye the specimen is a female; if drastically larger, the specimen is a male. 

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All and all, though very similar, these two species are still quite different. I hope this helps you better understand these differences, and hopefully now you can keep this in your mental database for your next encounter with one of these frogs. Feeling confident? Test you ability at the button below!​

Bullfrog vs Green Frog Quiz