Green frog (Lithobates clamitans)
|Size||Length: 6 - 9 cm (2)|
The green frog is classified as Least Concern (LC) on the IUCN Red List (1).
The green frog (Lithobates clamitans) is a relatively abundant North American amphibian. Similar to the bullfrog (Lithobates catesbeiana) in appearance (2) (3) (4), the green frog is easily distinguished by its slightly smaller size and the presence of two distinctive ridges that run from each eardrum, down both sides of the back (2) (5) (6) (7).
The green frog is typically brownish-green, often with dark mottling under the legs and on the head, chin and chest (2) (6). There are usually dark markings on the back (2) (5), and the underside of this species is whitish (4) (7). The throat of the green frog is generally yellow in the male (2) (6) (7) and white in the female (7).
There are two recognised subspecies of the green frog, the northern green frog (Lithobates clamitans melanota) and the bronze frog (Lithobates clamitans clamitans), which differ slightly in range and colouration (5) (8). The northern green frog can be distinguished from the bronze frog by the green rather than bronze colouration on its back, and by its slightly larger size (5).
As in many other frog species, the gender of an individual green frog can be determined by the size of the frog’s eardrum, the tympanum, relative to the size of its eyes. The tympanum is located almost directly behind the eye and is often quite large and visible (5). In the male green frog the tympanum is considerably larger than the eye, while in the female the eye and the tympanum are of relatively equal size (2) (3) (5). The male can also be distinguished by the presence of enlarged pads on the thumbs during the breeding season (6), and by its paired vocal organs (2).
Green frogs call throughout the day and night, producing as many as six different calls (4). The most distinctive vocalisation of the green frog is a single loud, throaty ‘gunk’ or ‘boink’, that is often likened to the sound of a loose banjo string being plucked (2) (3) (4).
The green frog is native to North America (4). It is found throughout the Maritime Provinces in eastern Canada, and in most of the eastern United States from the Canadian border south to the Gulf of Mexico (4) (8).
The green frog occurs in a variety of habitats. It is a highly aquatic species (2), being found in most permanent water bodies, including springs, streams, ditches, and the margins of ponds and lakes (1) (4) (6). It also inhabits shallow, freshwater wetlands, fens, bogs, swamps and marshes (3) (4) (7) (8).
Adult green frogs are typically found close to dense emergent vegetation, such as sedges, cattails and rushes, and will rarely venture further than a metre from the water (8), except on rainy nights (1) (8). Juvenile green frogs are more terrestrial than the adults and tend to occur in areas of less dense vegetation (8). The green frog will seek cover under objects on land, underground, or in water when inactive (1).
The green frog is a primarily nocturnal amphibian, but may sometimes be active during the day (4). As in other frogs, the green frog has fairly well developed senses (2) (4), with highly sensitive hearing (2) and bulging eyes that give a wide range of vision, aiding in the capture of prey (4).
Like most frogs, the green frog is an opportunistic feeder (8). It is a ‘sit-and-wait’ predator, and takes any prey species that is small enough to swallow (8), including insects, worms, molluscs, crustaceans, small fish and even other frogs, as well as plant material and shed animal skins (2) (4) (8). Green frog tadpoles are feed almost continuously (9), eating mainly algae (2) (9), although they will also occasionally feed on fungi and other organisms (8).
During the non-breeding season the green frog is mostly solitary (4). During the breeding season male green frogs become territorial (2) (4) (8), and will defend their territories against other males using vocalisations, posturing and physical combat (4) (8). The male green frog will set up a territory in the shallow water of a lake, pond, ditch or stream (2), and will usually live there for between one and seven weeks (8).
The green frog generally breeds between April and July (2) (4) (7) (8), although the exact timing of breeding depends on the location and in some areas may extend into late summer (8). The female lays around 3,000 to 4,000 eggs (2) in shallow, slow-flowing water (1) (4) (8), usually among emergent vegetation (4) (8). The eggs of multiple females will often coalesce into a single floating mass on the water’s surface (4) (8).
The eggs of the green frog usually hatch into tadpoles after three to seven days (2) (4). Larval green frogs may take anywhere between 3 and 22 months to metamorphose into the adult form, with most populations overwintering as tadpoles before metamorphosing the following summer (2) (4) (8). During metamorphosis, the tadpole develops its hind legs first, before absorbing its tail, losing its gills and forming lungs and other internal organs (4).
Some populations of the green frog are threatened by habitat loss and degradation (4), particularly as shorelines throughout its range have been developed for recreational, business and domestic use (4) (8). Collisions with road vehicles may also contribute to green frog mortality (8).
In addition, frogs and other amphibians are very sensitive to toxins and pollutants within their habitat. As a result, some populations of the green frog could potentially be at risk should the level of contaminants in their environment increase in future (4).
The green frog is relatively common throughout most of its range (8), and no known conservation measures are currently in place for this species.
The green frog is classified as a ‘Game Species’ in some states, including Missouri, Mississippi, Massachusetts, New York, New Jersey and Pennsylvania, which, due to imposed bag limits and restrictions in the length of the hunting season, may provide some level of protection for this species (8).
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- Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
- Crustaceans: diverse group of animals with jointed limbs and a hard external skeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
- Emergent: aquatic plants whose stems and leaves extend beyond the water’s surface.
- Larvae: the stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Metamorphosis: an abrupt physical change from the larval to the adult form.
- Molluscs: a diverse group of invertebrates, mainly marine, that have one or all of the following: a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
- Nocturnal: active at night.
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- Territorial: describes an animal, a pair of animals or a colony that occupies and defends an area.
- Tympanum: also known as the eardrum. A thin membrane that transmits sounds from the air to the middle ear.
IUCN Red List (June, 2012)
Minnesota Department of Natural Resources - Green frog (June, 2012)
Maryland Department of Natural Resources - Northern green frog (June, 2012)
Rosamund Gifford Zoo - Northern green frog (June, 2012)
USGS Checklist of Amphibian Species and Identification Guide - Green frog (June, 2012)
Illinois Natural History Survey - Green frog (June, 2012)
Michigan Department of Natural Resources - Green frog (June, 2012)
AmphibiaWeb - Green frog (June, 2012)
- Jenssen, T.A. (1967) Food habits of the green frog, Rana clamitans, before and during metamorphosis. Copeia, 1: 214-218.