Amphibians
Green Frog
Lithobates clamitans · also called northern green frog, bronze frog
The green frog is the everyday frog of eastern North America — the one sitting in the shallows at the edge of the pond, the one that twangs like a loose banjo string on a June evening, and the one that shrieks and dives just as you notice it.
Overview
Lithobates clamitans lives along the margins of ponds, lakes, marshes, and slow streams across eastern North America. It is 5–10 cm long, green to bronze, with a pair of raised ridges running two-thirds of the way down its back. It is a sit-and-wait predator that eats almost anything it can swallow.
The call, and the ridges
The male’s call is a single low, abrupt “gunk” — like a plucked banjo string — given day or night through summer. The dorsolateral ridges are the fastest way to tell it from a young bullfrog, which has none and grows much larger. A male’s eardrum is bigger than its eye; a female’s is eye-sized.
Slow to grow
In the north the tadpoles often overwinter and take about two years to transform, and adults hibernate buried in pond-bottom mud. Startled from a bank, a green frog gives a sharp squawk and a splashing leap.
Status
Least Concern and abundant, using almost any permanent fresh water — one of the least threatened frogs on the continent.
Green Frog: common questions
How do I tell a green frog from a bullfrog?
Look for the ridges and the size. A green frog has a pair of raised skin folds running down each side of its back, from behind the eye about two-thirds of the way to the rump. A bullfrog has no such ridges; instead the fold curves down and around the back of the eardrum. Size helps too — an adult green frog is 5 to 10 cm, while a bullfrog reaches 15 to 20 cm, so a very large frog is a bullfrog. The calls are quite different as well, the green frog's single banjo twang against the bullfrog's deep, booming, three-part "jug-o-rum".
Why does the green frog call sound like a rubber band or a banjo?
The male produces the sound by forcing air across the vocal cords and inflating a single large vocal sac under the chin, and the resulting note is short, low-pitched, and slightly musical, with a quick drop in tone that the human ear reads as a "boing" or "twang". Because it is brief and does not carry far, a chorus of green frogs sounds like scattered plucks from around the pond rather than the continuous trilling or booming of many other frogs. Males call from just at the waterline, often well spaced out, each defending a small stretch of shore.
Are green frogs good to keep as pets?
They can be kept, and are sometimes sold, but they are demanding for a frog and better appreciated in the wild. They need a large tank with a big water area and a land section, cool clean water, a secure lid because they are strong jumpers, and a supply of appropriately sized live invertebrates and, for adults, the occasional pinky mouse or small fish. Wild-caught adults often settle poorly. Since the species is common and easily watched at any local pond, most people are better off leaving them where they are and enjoying the call on a summer evening.
What eats green frogs?
A great many things, which is why the species produces so many eggs and tadpoles. Adults are taken by herons, egrets, bitterns, kingfishers, water snakes, snapping turtles, raccoons, mink, otters, large fish such as bass and pike, and by bigger frogs, especially bullfrogs, which will eat any green frog that fits in the mouth. The eggs and tadpoles are eaten by fish, newts, dragonfly larvae, diving beetles, and wading birds. A green frog that survives to adulthood has beaten long odds, and even then most live only a few years in the wild.