Wood frogs range from 3.5 to 7.6 cm. They exhibit a number of different skin colors, usually browns, tans, and rust, but they can also be found in shades of green and gray. Females tend to be more brightly colored than males. In all cases, however, they can be distinguished by a black patch that extends over the tympanum (outer ear) to the base of the front leg. It is this characteristic that causes them to be referred to as frogs with the "robber's masks." They also have white spots on their upper lips. Most wood frogs have a light yellowish brown fold around their sides and mid-back. The underparts are yellowish and sometimes greenish-white, with male frogs having more bright colors on their thighs. They have two back ridges on either side that extend from behind the eye, down the side of the back, and to the legs. Males have two vocal sacs for calling. Females are much larger than males.
Wood frogs, Lithobates sylvaticus, are only native to the Nearctic region. They are found from northern Georgia and in isolated colonies in the central highlands in the eastern to central parts of Alabama, up through the northeastern United States, and all the way across Canada into Alaska. They are found farther north than any other North American reptile or amphibian. They are the only frogs found north of the Arctic Circle. (Conant and Collins, 1998)
Wood frogs are common in woodlands across their range. They are most commonly found in woodlands in the summer, under stones, stumps and leaf litter in the winter, and wood ponds in the breeding season.
The eggs have a very good tolerance of temperature and those that are laid in water that afterwards freezes are not killed. They develop once temperature rises again. The length of incubation for these eggs varies depending on temperature. If laid in cold waters, then development is slow, and lasts at least a month; if, however, the eggs are laid in waters with a higher temperature, the development is much quicker, lasting only 9 to 10 days. After about a week to a month the eggs hatch and tiny, almost black, tadpoles emerge. The tadpoles are about 38 to 48 mm in length. It can take them a further 61 to 115 days to undergo metamorphosis and become froglets. The froglets are usually very small. They develop into full grown, sexually mature, adults generally within the next 2 years.
Wood frogs breed very early in the spring. During this time males begin to call to attract females. They create a duck-like quacking sound, described by some as a "lot of chuckling". Once mates are chosen and breeding occurs, females lay a globular egg mass, most often in the deepest part of a pond. Each egg mass measures about 10 to 13 cm in diameter, and can contain from 1000 to 3000 eggs. The masses can either be attached to a twig or grasses, or they can be left afloat. After about a week the egg mass begins to flatten out, allowing it to rest on the surface of the water. The jelly around the eggs becomes green, creating a kind of camouflage. The mass then looks like a floating mass of green pond scum. The green color of the jelly is due to the presence of many small green algae. Tadpoles will undergo metamorphosis in 2 months and will reach sexual maturity in approximately 2 years.
Female wood frogs provide their eggs with yolk before laying them. Once the eggs are laid and fertilized, the parents abandon them.
No information is available on the lifespan of wood frogs.
Wood frog tadpoles have been shown to have the strongest powers of kin recognition yet discovered in amphibian young. These tadpoles can recognize their brothers and sisters using maternal and paternal factors. They have been documented (by marking them with dye and releasing them into natural habitats) to group together according to relatedness. This may be a survival mechanism allowing them the potential benefit of food, temperature control, and defense against predators.
Wood frogs tend to be very territorial. They generally occupy an area of about 100 square meters.
Wood frog males will actively search for females during the breeding season; however, they are unable to tell males from females by sight. Gender recognition is accomplished by the males embracing other frogs (regardless of gender) and releasing those that are not fat enough to be females full of eggs. If a male is embraced he will let out a loud croak. A female will also be let go if spawning has already occurred, because she is thin.
The call of a wood frog is often compared with the sound of a quacking duck or a squawking chicken. They tend to repeat the call several times in a row when trying to attract females.
Wood frogs provide important food for many animals as well as helping to control insect populations.
Wood frogs, along with other amphibians, are great indicators of environmental health. Recent population declines in species of amphibians should be of great concern. Wood frogs may also help to control pests.
Though wood frogs are fairly common in most areas of appropriate habitat, loss of habitat to agriculture and suburban development has put them on the list of "species of special concern" in some areas.
Wood frogs have perfected the cryogenic freezing process. In the winter, as much as 35-45% of the frogs body may freeze, and turn to ice. Ice crystals form beneath the skin and become interspersed among the body's skeletal muscles. During the freeze the frog's breathing, blood flow, and heart beat cease. Freezing is made possible by specialized proteins and glucose, which prevent intracellular freezing and dehydration.
Allison Poor (editor), University of Michigan-Ann Arbor.
Katie Kiehl (author), Michigan State University, James Harding (editor), Michigan State University.
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.
uses sound to communicate
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.
an animal that mainly eats meat
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
An animal that eats mainly plants or parts of plants.
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).
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.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
Living on the ground.
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
uses sight to communicate
Blaustein, A., S. Walls. 1995. Aggregation and Kin Recognition. American Naturalist, 121: 449-454.
Chenard, P. 1998. "Wood Frogs" (On-line). Accessed November 17th, 1999 at http://www.ednet.ns.ca/cgi-bin/redirmu/educ/museum/mnh/nature/frogs/wood.htm.
Conant, R., J. Collins. 1998. Reptiles and Amphibians. New York: Houghton Mifflin Company.
Dickerson, M. 1931. The Frog Book. Garden City, New York: Doubleday, Doran, and Company, Inc..
Mansker, A. 1998. "Critter of the Week: Rana sylvatica" (On-line). Accessed November 17, 1999 at http://think.ucdavis.edu/~yamara/ucdlife/traditions/critters/rana.html.
Savage, R. 1961. The Ecology and Life History of the Common Frog. London: Sir Isaac Pitman and sons, LTD..