Anyone who has gone near a pond or lake during the summer has seen a green frog by the shore at some point. The caveat is that there are two different species of frogs that are green in color. Though the sound they make is different, they are very similar in appearance. One carries the name of its color, the green frog (Lithobates clamitans); the other is the bullfrog (Lithobates catesbeianus).

Green frogs are probably the most abundant frogs in the region and are two to four inches in length. Even if not breeding, their occasional “gulp” call can be heard through the summer. They usually have a green snout and head, and may have green patterns on their back. However, many individuals have a green head with a brown back. Their call is kind of a “gulp,” but sometimes can carry on into multiple notes or something like “jug-o-rum.”

Bullfrogs are abundant in the region and are the largest frogs you will see; they can grow to over eight inches long. The call of a bullfrog is a very distinct, low-pitched “rumm…rumm…rumm,” and is usually loud enough to carry across a good-sized lake. Their color patterns can vary from a green to a mottled green and brown pattern that is similar to the green frog.

The best way to tell the difference between these two species is to look at their backs, starting just behind each eye. Glandular folds of skin are present on both species; they are very prominent ridges and easily seen up close or with binoculars. The green frog has folds running from behind each eye to the base of each hind leg (these are called “dorsolateral ridges”). Bullfrogs have the glandular folds behind each eye but they only hook around the rear of each tympanum (ear).

Some frogs, especially bullfrogs, can appear to have pronounced hip bones forming what almost looks like a swayback condition in a horse, but don’t worry; you don’t have to call your equine vet for the frogs in your pond. Both species have winged sacral vertebrae and two attached ilial bones to act as underpinnings to support the thrust generated by powerful rear legs when a frog jumps clear of danger.