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Lithobates clamitansGreen Frog

By Merritt Gillilland

Geographic Range

Green frogs (Lithobates clamitans clamitans) are native only to the Nearctic region. They are found in the United States and Canada from Maine and the Maritime provinces of Canada through the Great Lakes region and into western Ontario and Oklahoma, south to eastern Texas, east into northern Florida and extending up the entire east coast of the United States. (Harding, 1997)

Habitat

Green frogs are found in a wide variety of habitats that surround most inland waters, such as: swamps, wooded swamps, ponds, lakes, marshes, bogs, banks of slow moving rivers and streams, oxbow lakes, sloughs, and impoundments. Juveniles may disperse into wooded areas or meadows during times of rain. Green frogs overwinter in the water usually buried in the substrate. (Harding and Holman, 1992; Harding, 1997; Tyning, 1990)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Green frogs are green, greenish brown, brownish, yellowish green and olive, with some rare individuals being blue. They are generally brighter in front with small irregular black spots. Their legs have dark transverse bands. They are yellowish or white below, and males usually have a bright yellow throat. The tympanum (eardrum) is large; in males the tympanum is much larger than the eye and females tend to have a tympanum the same size as the eye. The dorso-lateral ridge is well defined and extends from the back of the eye posteriorly down the body. The toes are well webbed and the first fingers do not extend beyond the second. The tibia and femur are equal to ½ of the body length, which is 7.5 to 12.5 cm for adults. (Harding and Holman, 1992; Jordan, 1929; Tyning, 1990)

  • Sexual Dimorphism
  • sexes shaped differently
  • Range length
    7.5 to 12.5 cm
    2.95 to 4.92 in

Development

Eggs hatch in 3 to 7 days. After hatching, green frog tadpoles are usually green with small black dots and often have yellow bellies. It can take them anywhere from 3 to 22 months to begin metamorphosis into full grown frogs. Some undergo this transition before the winter, but many tadpoles go into hibernation and wait until the spring to transform. Green frogs reach their maximum size when they are 4 to 5 years old.

Reproduction

Female green frogs choose their mates based on the desirability of their territories for egg laying. Satellite males may also be present during the breeding period of green frogs. A satellite male is described as a smaller male, unable to acquire and defend territories, and it is often found in areas protected by a larger male. The satellite male will wait for the opportunity to mate with a female that is responding to the larger more dominant male frog's vocalizations.

Breeding takes place in late spring; variations in temperature and region can influence actual breeding times. The breeding season is 1 to 3 months long and occurs in a variety of habitats, such as swamps, ponds, marshes, bogs, and slow moving streams. Once a female has chosen a male, amplexus will begin. During amplexus, 1000 to 7000 eggs may be laid. The egg masses float on the water surface or hang from emergent aquatic vegetation. Wells (1976) has shown that multiple egg clutches are possible, the second egg clutch is on average smaller, with 1000 to 1500 eggs. Eggs hatch in 3 to 7 days and will complete the tadpole stage of development in 3 to 22 months. (Harding and Holman, 1992; Tyning, 1990; Wells, 1976)

  • Breeding interval
    Green frogs can have two or more clutches per season, with the second clutch producing significantly fewer eggs.
  • Breeding season
    Green frogs breed in late spring.
  • Range number of offspring
    1000 to 5000
  • Range time to hatching
    3 to 5 days

Female green frogs nurture their eggs inside their bodies before they are laid and fertilized. Once the eggs are laid, there is no further parental involvement in their development.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female

Lifespan/Longevity

Average lifespan in the wild is unknown, but captive animals can live to 10 years.

  • Range lifespan
    Status: captivity
    10 (high) years

Behavior

Green frogs are active during the day and at night. They become dormant during cold weather. Green frogs are mainly solitary, except during the breeding season, when they congregate at breeding ponds.

  • Range territory size
    0.66 to 29.22 m^2

Home Range

Males establish breeding territories and maintain them throughout the breeding period. Territories are found in shallow water and are reported to be 0.9 to 6.1 m in diameter. Males usually sing from selected areas inside their territories while occasionally patrolling the outside edges. (Tyning, 1990)

Communication and Perception

Green frogs produce as many as six different calls. Males attracting a mate give an advertisement call and a high-intensity advertisement call. Their advertisement call has been compared to the pluck of a loose banjo string. Male frogs defending a territory from an intruding male usually give aggressive calls and growls. The release call is given by non-receptive females and by males accidentally grabbed by another male. Finally, the alert call is given by males and females when startled or attacked by a predator.

Green frogs have an excellent sense of vision and use this to detect and capture prey. (Harding and Holman, 1992; Tyning, 1990)

Food Habits

Green frogs are primarily carnivores and eat a wide variety of insects and other invertebrates from both land and water, such as slugs, snails, crayfish, spiders, flies, caterpillars, butterflies, and moths. They also eat other vertebrates, such as small snakes and frogs. Green frogs practice "sit and wait" hunting and therefore eat whatever comes within reach. Tadpoles mainly eat diatoms, algae, and tiny amounts of small animals such as zooplankton (copepods and cladocerans). (Jenssen, 1967)

  • Animal Foods
  • amphibians
  • reptiles
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • terrestrial worms
  • aquatic crustaceans
  • zooplankton
  • Plant Foods
  • algae

Predation

Green frogs are preyed upon by a variety of animals. Tadpoles and eggs are eaten by leeches, dragonfly larvae, other aquatic insects, fish, turtles, and herons. Adult frogs are eaten by larger frogs, turtles, snakes, herons, other wading birds, raccoons, otters, mink, and humans.

Green frogs often look much like mink frogs where the two species occur together. This may be a form of mimicry because mink frogs have a musky skin secretion that makes them foul tasting to many predators. Green frogs do not have a foul taste, so may be taking advantage of their resemblance to mink frogs to avoid being preyed upon.

  • Anti-predator Adaptations
  • mimic

Ecosystem Roles

Green frogs are common and abundant and serve as a food source for many other animals. They also eat large quantities of insects and other animals, thus impacting their populations.

Economic Importance for Humans: Positive

Green frogs on occasion are harvested for food consumption, generally known as "frog legs". They are used by the scientific community in research and for educational purposes in biology classrooms from both high schools and colleges. (Harding, 1997)

  • Positive Impacts
  • food
  • research and education

Economic Importance for Humans: Negative

There are no known negative effects of green frogs.

Conservation Status

Green frogs are abundant throughout all of their range. Although limb deformities and other abnomalities have been reported in green frog populations, possibly as a result of water contamination, they are still numerous and widespread.

Other Comments

One population of green frogs is known as 'bronze frogs.' They are usually bronze or brownish in color and have fairly plain markings. They also tend to be smaller than other green frogs. Bronze frogs are found in the southeastern United States.

Contributors

Allison Poor (editor), University of Michigan-Ann Arbor.

Merritt Gillilland (author), Michigan State University, James Harding (editor), Michigan State University.

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

acoustic

uses sound to communicate

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

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.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

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.

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.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sexual

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

solitary

lives alone

swamp

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

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

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

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Harding, J. 1997. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor, Michigan: The University of Michigan Press.

Harding, J., J. Holman. 1992. Michigan Frogs, Toads, and Salamanders. East Lansing, Michigan: Michigan State University Museum.

Jenssen, T. 1967. Food Habits of the Green Frog, Rana clamitans, before and during metamorphosis.. Copeia, 1967: 214-218.

Jordan, D. 1929. Manual of the Vertebrate Animals. New York: World Book Company.

Tyning, T. 1990. Stokes Nature Guides: A guide to Amphibians and Reptiles. Boston, MA: Little, Brown and Company.

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

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