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Lithobates clamitansGreen Frog

By Greg Porter

Geographic Range

Green frogs (Lithobates clamitans) are native to much of the eastern United States as well as southeastern areas of Quebec, Ontario, New Brunswick, and Nova Scotia, Canada. In the U.S., they range from central Florida, northwards along the eastern seaboard, and as far west as central Minnesota, Iowa, Oklahoma, Texas, and all but the northeastern corner of Missouri. Green frogs have been introduced throughout Newfoundland, Vancouver Island, and isolated areas of Washington, Utah, Arizona, Montana, the Bahamas, and the Netherlands. (Dodd Jr., 2013; Shepard, 2004; Wilson, 1995)

Habitat

Green frogs inhabit various bodies of freshwater, including lakes, ponds, streams, springs, wetlands, and ephemeral pools. The land surrounding the bodies of water that they inhabit is usually thick with vegetation, such as reeds, grasses, sedges, small shrubs, and trees. Green frogs spend most of their time along shoreline ecotones, where they can hunt for terrestrial prey and still quickly access water to avoid terrestrial predators. Green frogs infrequently inhabit areas of cities and suburbs, and, very rarely, cave openings. During especially rainy periods, green frogs occasionally travel farther away from large bodies of water to forage. The abundance of certain insects that arise during or after rain is what drives this movement into new areas.

As green frogs mature, they generally move from shallow areas near the shore into deeper waters. However, the presence of American bullfrogs (Lithobates catesbeianus) in a given area often deters green frogs. As a result, green frogs may select suboptimal habitat in areas where American bullfrogs also occur. Activity time depends on the seasonal weather patterns and the overall climate of the geographical area. (Dodd Jr., 2013; Wilson, 1995)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • temporary pools

Physical Description

Green frogs are divided into two subspecies, which can be distinguished by their overall coloration: northern green frogs (Lithobates clamitans melanota) in the northern portion of their range and bronze frogs (Lithobates clamitans clamitans) in the southern portion of their range.

Northern green frogs have abdomens that are dark green, brown, or sometimes black in color. Some individuals also have black spots on the dorsal side of their abdomens and legs. Some northern green frogs are such a dark color in the northern part of their range that they are called black frogs. Northern green frogs have large dorsolateral folds that go from their eyes halfway down their bodies. Their heads are lighter green compared to their bodies and they have bright yellow throats and light-colored bellies. They also have a dark band along each of their sides, which transitions into a pattern of multiple dark stripes on their legs.

Bronze frogs have more bronze coloration over most of their bodies and they lack the black spotting that some northern green frogs have. Their heads and bellies are nearly the same as northern green frogs, but their throats are paler yellow. There are rare observations of albino individuals, or individuals with orange or blue coloration. Most of these observations are of northern green frogs, although these color morphs are also possible in bronze frogs.

Adult green frogs throughout their range measure 56 to 105 mm in snout-vent length (SVL). However, northern green and bronze frogs vary in body size, with bronze frogs being smaller and thinner than northern green frogs. Bronze frogs measure 60 to 70 mm in SVL while northern green frogs reach 80 to 85 mm. Weights vary wildly with factors such as the amount of time a frog is active throughout the year and food availability. These numbers may be as low as 28 g, but usually do not exceed 85 g. Tadpoles are thin, but very long at an average of 90 mm.

Green frog tadpoles are dark green on the dorsal side of their bodies, with tails that are dark green or brown with dark spots. Their throats are white and the ventral side of their bodies white or cream. Adult males and females are generally the same size, though they do exhibit sexual dimorphism in features such as their tympanums, thumbs, and forearms. Males have much larger tympanums relative to the size of their eyes, whereas females have tympanums that are nearly equal in size to their eyes. Males also have much larger thumbs and forearms than females, which is important for mating purposes.

The dorsolateral folds that green frogs have distinguish them from other frogs of similar size and color, such as American bullfrogs (Lithobates catesbeianus), and mink frogs (Lithobates septentrionalis). (Dodd Jr., 2013)

  • Sexual Dimorphism
  • sexes shaped differently
  • Range mass
    28 to 85 g
    0.99 to 3.00 oz
  • Range length
    56 to 106 mm
    2.20 to 4.17 in

Development

Female green frogs lay eggs that hatch 3 to 6 days after fertilization. Newly hatched larva, also called tadpoles, generally remain in their larval stage for around 3 months before metamorphosis occurs. During metamorphosis, tadpoles gradually lose their tails and develop front and back legs, at which point they are considered juveniles. Newly metamorphosed juveniles measure 25 to 35 mm in snout-vent length (SVL) and will grow the most over their first year, reaching around 60 mm in SVL. After their first year, their growth rate slows to an average of 17 mm a year. Upon reaching an SVL of 60 to 70 mm, green frogs are considered sexually mature adults. Green frogs exhibit indeterminate growth, but their annual growth rate slows to 2 mm per year upon reaching sexual maturity, with some individuals reaching 90 to 105 mm in SVL. (Dodd Jr., 2013; Lannoo, 1998; Martof, 1956)

Reproduction

Male green frogs call more frequently during the mating period. This calling becomes even more frequent if they have failed to mate between July and September. When selecting a mate, females take male size and territory into account. Larger males make calls with lower frequencies, which provides an indication of male body condition before females see them. Better quality male territories usually have more dense foliage, and larger males generally inhabit these territories more often than smaller males. Some smaller males, referred to as "satellite" males, stay near but not in the territories of other males until those territories are vacated. Large males with larger, more dense territories mate more often than smaller males. However, mating is not guaranteed regardless of body size or territory quality. Both males and females may mate multiple times over the course of a single mating season.

Mating occurs in shallow areas of bodies of water. Mating pairs engage in amplexus, a mating position in which males mount females, using their enlarged thumbs and forearms to clasp females from behind. At some point during amplexus, females lay their eggs and males fertilize eggs externally. After eggs are fertilized, males use their back legs to push them away. Total mating time ranges from 10 to 25 minutes, depending on the number of eggs that females produce. When a pair finishes mating, they give off warning calls to let other frogs know they are temporarily unavailable to mate. (Dodd Jr., 2013; Lannoo, 1998)

Male green frogs call most often during the mating period. This calling becomes even more frequent if they have failed to mate between July and September. When selecting a mate, females take male size and territory into account. Larger males make calls with lower pitches, which provides an indication of male body size and fitness before females see them. Better quality male territories usually have denser vegetation, and larger males generally inhabit these territories more often than smaller males. Some smaller males, referred to as "satellite" males, stay near but not in the territories of other males until those territories are vacated. Large males with larger, more dense territories mate more often than smaller males. However, mating is not guaranteed regardless of body size or territory quality. Both males and females may mate multiple times over the course of a single mating season.

Mating occurs in shallow areas of bodies of water. Mating pairs engage in amplexus, a mating position in which males mount females, using their enlarged thumbs and forearms to clasp females from behind. At some point during amplexus, females lay their eggs and males fertilize eggs externally. After eggs are fertilized, males use their back legs to push them away. Total mating time ranges from 10 to 25 minutes, depending on the number of eggs that females produce. When a pair finishes mating, they give off warning calls to let other frogs know they are temporarily unavailable to mate. (Dodd Jr., 2013; Lannoo, 1998)

Green frogs have a breeding season that usually runs from April to July, but may last until September in southern portions of their range. While females typically reach sexual maturity by 1 year following metamorphosis, males usually require another 6 months before reaching full maturity. Males can mate up to 5 times in one breeding season. Most females only mate once per year, although some mate a second time depending on how early in the breeding season they lay their first egg clutch. Egg clutch size ranges from 1,000 to 7,000 eggs; females that mate a second time lay an additional clutch of 1,000 to 1,500 eggs. Occasionally, clutches from multiple females merge together, creating masses of nearly 20,000 eggs. Eggs hatch 3 to 6 days after they are laid and newly hatched tadpoles are immediately independent from their parents. Females leave the breeding areas around a week after mating, whereas males may remain for up to 2 months. Males likely remain in mating areas to defend their territories rather than protect their offspring. (Dodd Jr., 2013; Lannoo, 1998)

  • Breeding interval
    Green frogs generally mate once per year, but some females may mate twice and males may mate up to five times.
  • Breeding season
    April to September
  • Range number of offspring
    1,000 to 8,500
  • Range time to hatching
    3 to 6 days
  • Average time to hatching
    5 days
  • Range time to independence
    0 (low) days
  • Range age at sexual or reproductive maturity (female)
    1.25 to 2 years
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Range age at sexual or reproductive maturity (male)
    1.5 to 2 years

Green frogs exhibit no known parental investment beyond the act of mating. (Dodd Jr., 2013; Lannoo, 1998)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

A study on green frogs in south-central Indiana reported population turnovers every 5 to 6 years. In captivity, green frogs are reported to live up to 10 years. (Lannoo, 1998; Partners in Amphibian and Reptile Conservation, 2011)

  • Range lifespan
    Status: captivity
    10 (high) years
  • Typical lifespan
    Status: wild
    5 to 6 years
  • Average lifespan
    Status: wild
    5 years

Behavior

Green frogs are more active during the day, though they also hunt at night. Male green frogs are aggressively territorial. Encounters usually start with intimidation in which a male defending its territory will display its bright yellow throat to deter approaching males. If an intruding male persists despite this warning, the two males grapple with each other for anywhere from a few minutes to almost an hour, until one surrenders and leaves the disputed territory. Other territory defense behaviors include kicking, biting, head-butting, and making aggressive calls that resemble growls. Occasionally, small communes of males work together to collectively hold a territory much larger than normal.

Although uncommon, large male green frogs may attempt to hold anywhere from 1 to 5 territories at once. They move throughout their territories, remaining in each for a few weeks throughout the year. Larger males usually stay in their home territory during breeding season, rather than venturing for a temporary breeding ground. Green frogs exhibit more territorial aggression during the breeding season, especially if males remain stationary. Outside of breeding season, however, males generally move about as needed, without opposition from other males.

Green frogs enter brumation at some point in nearly all phases of their life cycle. Most tadpoles brumate and wait for warm weather before they undergo metamorphosis. However, in southern parts of their geographic range, tadpoles may remain active year round, depending on the local climate. Adults and juveniles brumate on land, often in light soil or organic matter cover, or in water. Aquatic brumation is more common, but green frogs require specific conditions at aquatic sites. Namely, aquatic sites must not freeze completely and must have sufficient levels of oxygen for green frogs to breathe throughout brumation. (Dodd Jr., 2013; Lannoo, 1998; Owen and Perrill, 1998; Shepard, 2004; Wells, 1977)

  • Range territory size
    4 to 6 m^2

Home Range

A typical territory size for a male green frog is between 4 and 6 m^2. Males occasionally travel away from their specific territory to hunt, though they usually move no more than 50 m away. (Dodd Jr., 2013; Lannoo, 1998)

Communication and Perception

Green frogs communicate mostly by producing acoustic calls. The sound of their call is most commonly compared to the plucking of a loose banjo string. There are generally 4 call types that frogs will use in various situations: short single calls, aggressive short calls, small burst calls, and prolonged single calls. Short, single calls are most common, and are used more frequently as mating season progresses. Males produce calls that vary in pitch depending on their body size, with larger frogs producing deeper calls. Females use this difference in call pitch to discern the size and fitness of potential mates, while males listen to the calls of other males to delineate territory boundaries. In non-combative territory disputes, males produce short single calls, but typically with a slightly lower tone in an attempt to intimidate or deter approaching males. Green frogs may produce groups of 3 to 4 calls in a row during times of stress or as warning calls. After combative territory disputes between two males, the winner often produces a call that is similar to their normal call, but slightly deeper and more prolonged. Green frogs use a special call after they finish mating to inform nearby frogs that they have already mated.

Green frogs likely perceive colors well and also have good hearing. Evidence for color perception comes from observations of their strong reactions to colors in the blue spectrum over others. Their eyes are also sensitive to both sun and moonlight. This allows them to move around and hunt diurnally or nocturnally, identify prey easily, and find bodies of water. (Bee and Perrill, 1996; Dodd Jr., 2013; Owen and Perrill, 1998)

Food Habits

Green frogs have a varied diet that consists mainly of moths, snails, and small fish. They opportunistically consume other animals that fit in their mouths, including arthropods, mollusks, amphibians, and reptiles. While adult frogs tend to go for large prey, juveniles will eat organisms much smaller than themselves. Tadpoles mainly eat diatoms, but also eat other algae, protozoans, and microcrustaceans. (Dodd Jr., 2013; Jenssen and Klimstra, 1966)

  • Animal Foods
  • amphibians
  • reptiles
  • fish
  • eggs
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • terrestrial worms
  • Plant Foods
  • algae

Predation

Northern green frogs exhibit Batesian mimicry to deter predators. Their color and patterning closely resembles that of mink frogs (Lithobates septentrionalis), which occur in the same areas and emit a foul odor resembling rotting onions when threatened. The foul smell that mink frogs produce deters many predators, so northern green frogs may benefit from their close resemblance to mink frogs where the two species are sympatric. Green frogs can also swell their throats to appear larger than normal when threatened. They also produce loud, sharp squawks when fleeing predators. Such calls may startle predators and give green frogs a better chance to escape.

Known predators of green frogs include American bullfrogs (Lithobates castbeianus), crows (genus Corvus), herons (family Ardeidae), American minks (Neovison vison), river otters (Lontra canadensis), raccoons (Procyon lotor), common snapping turtles (Chelydra serpentina), Blanding's turtles (Emydoidea blandingii), cottonmouths (Agkistrodon piscivorus), northern water snakes (Nerodia sipedon), common garter snakes (Thamnophis sirtalis), ribbon snakes (Thamnophis sauritus), catfishes (genus Ictalurus), black basses (genus Micropterus), rock bass (Ambloplites rupestris), crayfishes (infraorder Astacidea), diving beetles (genus Dytiscus), water beetles (family Hydrophylidae), whirligig beetles (family Gyrinidae), giant water bugs (family Belostomatidae), water scorpions (family Nepidae), backswimmers (family Notonectidae), humans (Homo sapiens), and ostracod species including Dolerocyprts sinensis, Cypridopsis vidua, Eucypris fuscatus, and members of the genus Physocypria. (Dodd Jr., 2013; Fracker, 2010; Lannoo, 1998)

  • Anti-predator Adaptations
  • mimic
  • cryptic

Ecosystem Roles

Green frogs are predators of many aquatic and terrestrial insect species, and likely play a role in controlling their populations. Green frogs also serve as prey for crustaceans and other vertebrates, both as tadpoles and as adults.

Green frogs are affected by the fungal disease chytridiomycosis, caused by the fungus Batrechochytrium dendrobatidis. They are also affected by flukes (Glypthelmins quieta), digeneans (subclass Gorgoderina), tapeworms (family Proteocephalidae), thorny- or spiny-headed worms (phylum Acanthocephala), trypanosomes (Trypanosoma rotatorium), and nematodes (phylum Nematoda). One family of parasitic protozoans, Opilinidae, is most common in tadpoles. Additional protozoan parasites include species in the genera Octomitus and Nyctotherus. Additionally, mosquitoes such as Culex territans feed on the blood of green frogs. (Fortner, 1923; Hazard, 1941; Lannoo, 1998; Longcore, et al., 2007)

Commensal/Parasitic Species
  • Fungus Batrechochytrium dendrobatidis
  • Flukes (Glypthelmins quieta)
  • Digeneans (subclass Gorgoderina)
  • Tapeworms (family Proteocephalidae)
  • Thorny- or spiny-headed worms (phylum Acanthocephala)
  • Trypanosomes (Trypanosoma rotatorium)
  • Nematodes (order Nematoda)
  • Protozoa (family Opilinidae)
  • Protozoa (genus Octomitus)
  • Protozoa (genus Nyctotherus)

Economic Importance for Humans: Positive

Green frogs are a source of frog legs for human consumption. They are not toxic and are considered very palatable. (Dodd Jr., 2013)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known adverse effects of green frogs on humans.

Conservation Status

Green frogs have stable population sizes throughout their range. They are listed as a species of "Least Concern" on the IUCN Red List and have no species status on the CITES appendices or any other international or national conservation list. However, in Kansas, green frogs are listed as a threatened species in a limited area. Missouri, Mississippi, Massachusetts, New York, New Jersey, and Pennsylvania have listed green frogs as game animals, which gives them extra protection regarding hunting regulations and restrictions. (Hammerson, 2004; Lannoo, 1998)

Contributors

Greg Porter (author), Radford University, Karen Powers (editor), Radford University, April Tingle (editor), Radford University, Emily Clark (editor), Radford University, Cari Mcgregor (editor), Radford University, Jacob Vaught (editor), Radford University, Genevieve Barnett (editor), Colorado State University, Galen Burrell (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

insectivore

An animal that eats mainly insects or spiders.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

marsh

marshes are wetland areas often dominated by grasses and reeds.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

Bee, M., S. Perrill. 1996. Responses to conspecific advertisement calls in the green frog (Rana clamitans) and their role in male-male communication. Behaviour, 133/(3-4): 283-301.

Dodd Jr., C. 2013. Frogs of the United States and Canada. Baltimore, Maryland: Johns Hopkins University Press.

Fortner, H. 1923. The distribution of frog parasites of the Douglas Lake region, Michigan. Transactions of the American Microscopical Society, 42/2: 79-90.

Fracker, M. 2010. Risk assessment and anti-predator behavior of wood frog (Rana sylvatica) tadpoles: A comparison with green frog (Rana clamitans) tadpoles. Journal of Herpetology, 44/3: 390-398.

Gray, E., S. Nunziata, J. Snodgrass, D. Ownby, J. Havel. 2010. Predation on green frog eggs (Rana clamitans) by Ostracoda. Copeia, 2010/3: 452-456.

Hammerson, G. 2004. "The IUCN Red List of Threatened Species. Version 2014.3" (On-line). Lithobates clamitans. Accessed March 20, 2015 at http://www.iucnredlist.org/details/58578/0.

Hazard, F. 1941. The absence of Opalinids from the adult green frog, Lithobates clamitans clamitans. The Journal of Parasitology, 27/6: 513-516.

Jenssen, T., W. Klimstra. 1966. Food habits of the green frog, Lithobates clamitans clamitans, in Southern Illinois. American Midland Naturalist, 76/1: 169-182.

Lamoureux, V., J. Maerz, D. Madison. 2002. Premigratory Autumn foraging forays in the green frog, Lithobates clamitans clamitans. Journal of Herpetology, 36/2: 245-254.

Lannoo, M. 1998. Status and conservation of midwestern amphibians. Iowa City, Iowa: University of Iowa Press.

Longcore, J., J. Longcore, A. Pessier, W. Halteman. 2007. Chytridiomycosis widespread anurans of Northeastern United States. The Journal of Wildlife Management, 71/2: 435-444.

Marino, Jr., J., E. Werner. 2013. Synergistic effects of predators and trematode parasites on larval green frog (Rana clamitans) survival. Ecology, 94/12: 2697-2708.

Martof, B. 1956. Growth and development of the green frog, Lithobates clamitans clamitans, under natural conditions. American Midland Naturalist, 55/1: 101-117.

Muzzall, P., M. Gillilland, III, C. Summer, C. Mehne. 2001. Helminth communities of green frogs Rana clamitans Latreille, from southwestern Michigan. The Journal of Parasitology, 87/5: 962-968.

Owen, P., S. Perrill. 1998. Habituation in the green frog. Behavioral Ecology and Sociobiology, 44/3: 209-213.

Partners in Amphibian and Reptile Conservation, 2011. "Partners in Amphibian and Reptile Conservation" (On-line). Accessed April 02, 2015 at http://www.parcplace.org/.

Schulte-Hostedde, A., C. Schank. 2009. Secondary sexual traits and individual phenotype in male green frogs (Rana clamitans). Journal of Herpetology, 43/1: 89-95.

Shepard, D. 2004. Seasonal differences in aggression and site tenacity in male green frogs, Lithobates clamitans clamitans. Copeia, 2004: 159-164.

Southworth, G., G. Mason, J. Seed. 1968. Studies on frog Trypanosomiasis. I. A 24-hour cycle in the parasitemia level of Trypanosoma rotatorium in Rana clamitans from Louisiana. The Journal of Parasitology, 54/2: 255-258.

St-Amour, V., T. Garner, A. Schulte-Hostedde, D. Lesbarreres. 2010. Effects of two amphibian pathogens on the development stability of green frogs. Conservation Biology, 24/3: 788-794.

Wells, K. 1976. Multiple egg clutches in the green frogs (Rana clamitans). Herpetologica, 32/1: 85-87.

Wells, K. 1977. Territoriality and male mating success in the green frog (Rana clamitans). Ecology, 58/4: 750-762.

Wilson, L. 1995. The Land Managers Guide to the Amphibians and Reptiles of the South. Chapel Hill, North Carolina: The Nature Conservancy.

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