Sunday, May 27, 2012

A Green Frog and a Bullfrog....and the differences between frogs and toads...

After posting the photos of the Fowler's Toad (click here for that post), I had a lot of emails from readers asking how to tell a toad and frog apart, so I thought I'd put something together quickly to explain. Let's start with two frogs I recently photographed while I was up at Magee Marsh for the Biggest Week in American Birding. After you see a couple of frogs, we'll move on to telling frogs and toads apart. The first frog is a Green Frog...

Female Green Frog (Rana clamitans melanota)
The easiest way to identify a Green Frog is to study the length of the dorso-lateral fold. Notice the fold of skin that starts just behind the eye, goes over the tympanum (ear drum disc behind the eye) and runs the length of the body. This ridge is the lateral fold. On Green Frogs, it runs the length of the body.

Green Frogs (Rana clamitans melanota) and Bullfrogs (Rana catesbeiana) are both green, and a small Bullfrog can look a lot like a Green Frog, but if you look at the lateral fold, there is no mistaking the two. On a Bullfrog, the dorso-lateral fold curls around the tympanum....

Male Bullfrog (Rana catesbeiana)
Notice how the lateral fold curls around the tympanum (eardrum disc next to the eye) and does not extend down the length of the back. Young Bullfrogs can resemble Green Frogs; however, as soon as you check out the lateral fold, you'll know which frog is which!

Telling a male frog from a female frog
There is an easy trick for determining the sex of a Green Frog and a Bullfrog. Look at the tympanum behind the eye. Female tympanums are about the same size as the eye. Male's are almost twice as big!
Note: This little trick works only for Green Frogs and Bullfrogs. The tympanum on most other frogs and toads is slightly smaller than the eye.

To determine the sex of a Green Frog or a Bullfrog compare the tympanum (ear drum) to the eye. A female's tympanum is about the same size as the eye; a male's is almost twice as large! I wish this trick worked for all frogs and toads! (Pencil sketch from my sketchbook.)


What are the differences between a frog and a toad?
Scientifically, there really is no difference between a frog and a toad--both are amphibians in the order "Anura." Morphologically, however, you can see physical differences between the two, and because of that, scientists have classified them into different families. The following characteristics separate "true frogs" (family Ranidae) from "true toads" (family Bufonidae)...
  • Skin   Frogs usually have wet and smooth skin because they rarely leave the water. Toads usually have dry and bumpy or warty skin because they prefer to live in damp locations away from the water. 
  • Legs   Frogs have long legs and feet, and they can jump far. Toads have shorter legs and can hop, but they can't jump that far. Toads tend to walk around or make little hops. 
  • Parotoid gland   Some frogs are poisonous to the touch, but only toads have the large parotoid gland behind the eyes that secretes a toxin that can burn the mouth and mucous membranes of a predator. 
  • Body shape   Frogs tend to be leaner and more streamlined for swimming. Toads are often described as being "chubby" or squat.
  • Eggs   Frogs usually lay eggs in clusters or mats. Toads tend to lay eggs in chains. 
  • Eyes   Frogs are said to have more prominent or "buggy" eyes. Toads less so (for me, the bugginess of the eyes is harder to distinguish. They all look pretty buggy to me!).
The differences between a frog and a toad become apparent when you place them side by side. Toads definitely look chubbier, but the Parotoid gland is what really separates them for me. When I see that poison pouch, I know I'm looking at a toad, and if I see a lateral fold, I know I'm looking at a frog. (Pencil sketch from my sketchbook.) 

These characteristics are generalities and blur quickly when you look at all the Anura families. For example, a Blanchard's Cricket Frog looks a little toady at first glance. He's bumpy and muddy looking and can be found away from water, but if you look for a Parotoid gland you won't find one, because he's a frog...not a toad! (Click here for a post on Cricket Frogs. Click here to learn about the Parotoid gland on a toad.) In Ohio, you can find the following Anuran families:

Ranidae ("true frogs") - Bullfrog, Green Frog, Leopard Frog, Pickerel Frog, Wood Frog
Hylidae - Gray Treefrogs, Chrous Frogs, Spring Peeper, and Cricket Frog
Bufonidae ("true toads") - American Toad, Fowler's Toad
Scaphiopodidae - Eastern Spadefoot Toad

For a complete list of Anuran families, click here.

Sources
  • Minton, Sherman A (2001). Amphibians & Reptiles of Indiana, Indiana Academy of Science. ISBN 1-883362-10-5
  • Platt, Carolyn V. (1998). Creatures of Change, An Album of Ohio Animals, The Kent State University Press. ISBN 0-87338-585-3
  • Ohio Division of Wildlife, "Amphibians of Ohio Field Guide." Click here for a free online PDF of this guide. 

11 comments:

Appalachian Lady said...

Great post. I will now look at our bullfrog a little closer to see the difference.

Kerri said...

GREAT info!!!
Great pics!

Roy said...

Interesting! On my walk through the wetlands park yesterday I also got a sound recording of the Green Frogs in the swamp barking and bellowing at each other; it really sounded like there was a regular brawl going on in there. Unfortunately the recording didn't turn out so well, so you didn't get to hear it; quality control is tough in this studio!

Randy Emmitt said...

Kelly,
I'm hearing both Green and Bullfrogs right now in our pond. Always had a time telling them apart by sight, thanks for the tips.

Adrienne in Ohio said...

Kelly, Have you thought of writing a children's book? Your illustrations are so helpful and your explanations are so well-written and easy to understand. I love your sketches!

Hilke Breder said...

Finally getting a chance to catch up with your posts, Kelly. Thanks for sharing the info on frogs and toads - very helpful when I looked at a couple of pics in my archive of bull frogs and a toad. Those warbler photos taken at the Magee Marsh are exquisite! I am green with envy! Maybe next year.....

Roy said...

Lovely drawings and lots of useful info Kelly, There is another way, "Frogs Hop, Toads Walk." {:))

Elaine said...

Beautiful photos and drawings! You've explained the differences so well and I know I will be able to tell a frog from a toad now. Of course, I won't have much chance to practice my ID skills for a while since when I see an amphibian here, whether it's in the water or in my flowerbed, I know it's a Wood Frog--because that's the only one we have here. So now we get to test my memory skills for the next time we're traveling and one of these little guys hops up to me....

Pasadena Adjacent said...

Now I have some information to arm myself when I see them. I'll need to bring a magnifying glass though. Ours are coming out in mass and they are tineeeee. Love your sketches.

Banjo52 said...

Your explanations are so clear that I might actually remember the frog-toad differences next time I see one. And yes, the sketches/diagrams are excellent. Thanks.

Jeane said...

Good job! this is indeed a very informative post. I really learned a lot about bullfrogs. Thanks!

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