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The northern green frog is a protected species whose range extends throughout most of eastern North America, east of central Oklahoma. It belongs to a group of amphibians, called anurans, which includes frogs and toads. Rana clamitans melanota inhabit ponds, lakes and permanent streams throughout the Bay watershed. Their familiar breeding call-a pronounced twanging sound like the pluck of a banjo string-can be heard from early spring through August along the quiet margins of ponds, streams and rivers.

Background

Photo by Mike Land

Rana clamitans melanota, the green frog common to the Chesapeake Bay, is one of more than 4,000 species of frogs that scientists have identified thus far. More species are being discovered every year, mostly in tropical zones. Frogs and toads are descended from salamander-like animals with elongated bodies, tails and short legs. The first species probably date to the Jurassic Period, from 206 million to 144 million years ago. Their antiquity and physiology have prompted biologists to study their habits and embryonic stages. Frogs are important bioindicators-the health of a given species can indicate or predict the status of its ecosystem.

Frogs have been found on every large landmass in the world except Antarctica. Species diversity increases in warmer climates; more species, for example, have been located in a single rain forest in South America than have been counted throughout North America. The largest species of frog is the West African goliath frog, which matures to a length of 12 inches and can weigh more than 7 pounds; the smallest frog yet identified is native to Brazil and weighs barely one ounce. The green frog native to the Chesapeake Bay is a medium-sized frog, usually 2 to 3.5 inches long.

Frog species usually require a moist habitat and have no scales to protect their delicate skin. They secrete a protective coating of mucus through their skin glands, and otherwise rely on acute vision and hearing to survive. Their protuberant eyes give them a wide range of vision, and their tympanums-large external eardrums-are sensitive.

Frogs breathe on land with their lungs, which they inflate using the movements of their throat, but oxygen also enters through their thin skin, which is netted with a system of blood vessels. While underwater, frogs breathe only through the skin. Their hearts have three chambers, two atria and one ventricle, which pumps oxygen-rich blood to the frog's lungs and the rest of the body.

Life Cycle and Habitat

The green frog looks something like a small bullfrog, with two parallel ridges or folds along its back. It can range in color from green or bronze to olive-brown (although blue specimens have been found), with a white underside and dark blotches on the back. Some males have bright yellow throats, and their tympanums are larger than those of females.

It's common for the green frog's mating period to extend from early spring to late August, with intense periods of mating during May and June. Although by habit both sexes are nocturnal, solitary, shy animals, males defend their territories actively at the edges of ponds and streams, and may physically or vocally attack intruders. A first mating takes place when the frog is usually between the age of 1 and 2 years. Females lay clutches of about 3,000 eggs in a filmy clump that floats on the water's surface. After fertilization, larvae take several months to hatch and transform into tadpoles and mature frogs, but some may overwinter if their habitat is a permanent body of water, not a ditch or puddle.

Tadpoles have dark coloration, usually brown to gray, with some darker spots. During metamorphosis the tadpole develops hind legs first, absorbs its tail, then loses gills and begins to form lungs and other internal organs. The tadpole's mouth, adapted for consuming algae, begins to develop a sticky, projecting tongue for catching insects. Once the transformation is complete, a mature frog may live in the wild for a couple of years. Bullfrogs live a few more years, and one species, native to Africa, has produced specimens that have lived as long as 35 years in captivity.

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Last modified: 03/01/2003