Green Frog

Lithobates clamitans melanota
Thursday, June 13, 2013

           The two most common large frogs at the station, the green frog and the bull frog can be quite difficult to distinguish. Although the two have different life histories and anatomies and fill different ecological niches, the simplest way to differentiate them is the presence of “dorsolateral ridges”—twin folds of skin forming raised lines from the frog’s eyes ⅔ of the way down its back. Bullfrogs lack these ridges entirely, whereas in other species they continue down to the frog’s groin. However, the confusion between species could only happen with bullfrogs that were not fully grown; adult bullfrogs are commonly 9-15 centimeters in length and have been known to approach 20, whereas the record length for a green frog is only 10.8 cm.

           The dorsal coloration of green frogs can be highly variable, ranging from brown to bronze to green, often with darker spots or mottling. The ventral is typically creamy-white or grey and also mottled. Unlike many other species, the center of the tympanum (eardrum) is raised, and in males it tends to be larger than their eye, while in females it is often the same size.

           The species name clamitans is derived from the Latin clamare—“to declare, call out, or cry out.” L. clamitans certainly can produce a clamor as it proclaims its territory at breeding sites or exclaims in alarm at a disturbance before vanishing beneath the water. Its call has been compared to the prolonged, low-pitched twang of a loose banjo string, and is often repeated several times growing progressively louder. Unlike bullfrogs, green frogs rarely sing in chorus.

           In late spring or early summer, green frogs migrate from their primary habitats to breeding sites in ponds or wetlands. As soon as the males arrive, they establish a territory and begin trying to attract females. When the females arrive, they can spend several days surveying all of the calling territories before selecting a male. After mating, females lay between 1,000 and 4,000 small black-and-white eggs in a gelatinous, elliptically-shaped envelope near the surface of the water. The eggs hatch in 3-6 days, depending on the temperature. Females often lay more than one clutch per year.

           The small tadpoles also closely resemble those of bullfrogs; at this stage, the best distinguishing feature is an abrupt color change from the pale ventral to the olive-green dorsal, whereas in bullfrogs it is more gradual. Tadpoles which hatch earlier in the summer metamorphose into their adult form before the winter and hibernate buried in flowing streambeds or underwater. However, tadpoles which hatch later in the summer often spend the winter hibernating in their larval form before metamorphosing the following spring. Green frogs seem to be complete opportunists concerning their food preference; they will lie in wait for any prey they can fit in their mouths. They eat all manner of insects, crustaceans, and even their own cast-off skin.

           This frog was found on the trail near the spring. He is a fully-grown male, judging by his relatively prodigious size and large tympanum.

Article by Hazel Galloway