Animal Diversity Web

Ge­o­graphic Range

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. (Co­nant and Collins, 1998)

• Biogeographic Regions
• nearctic
  • native

Habi­tat

Wood frogs in­habit a wide va­ri­ety of habi­tats in­clud­ing tun­dra, thick­ets, wet mead­ows, bogs, conif­er­ous and de­cid­u­ous forests. Wood frogs are aquatic breed­ers and re­quire fish-free sea­sonal or semi-per­ma­nent bod­ies of water to re­pro­duce, but will mi­grate from their pri­mary habi­tat to breed. These frogs seek out ter­res­trial lo­ca­tions with ample cover to hi­ber­nate which may or may not be near a breed­ing pond. (Red­mer and Trauth, 2005)

• Habitat Regions
• temperate
• polar
• terrestrial

• Terrestrial Biomes
• tundra
• savanna or grassland
• forest

• Aquatic Biomes
• temporary pools

Phys­i­cal De­scrip­tion

Wood frogs range from 3.5 to 7.6 cm. Fe­males are much larger than males. This species ex­hibits a num­ber of color morphs, usu­ally browns, tans and rust, but can also be found in shades of green and gray. In all cases how­ever, they can be dis­tin­guished by a black patch that ex­tends over the tym­pa­num to the base of the front limb. It is this char­ac­ter­is­tic that causes them to be re­ferred to as the frog with the "rob­ber's mask". They are also known to have a white out­line across the upper lip. Most spec­i­mens have a light yel­low­ish brown mid­dor­sal lat­eral fold. The un­der­parts of the frogs are white be­com­ing pale or­ange-yel­low to­wards the rear, with male frogs hav­ing more bril­liant col­ors on the ven­tral as­pect of the legs. (Dick­er­son, 1931; Mansker, 1998)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• female larger
• male more colorful

• Average mass

  7.88 g

  0.28 oz

  AnAge

• Range length

  3.5 to 7.6 cm

  1.38 to 2.99 in

• Average basal metabolic rate

  0.00416 W

  AnAge

De­vel­op­ment

The time it takes for fer­til­ized eggs to hatch is largely de­pen­dent on water tem­per­a­ture. Eggs that are laid in colder wa­ters in early March may take a month to hatch, whereas eggs laid later when water tem­per­a­tures are warmer may take only 10 to 14 days. Tad­poles are olive-brown to black in color and mea­sure 49.8 mm in length. Tad­poles un­dergo meta­mor­pho­sis when they reach 50 to 60 mm in length be­tween 65 and 130 days post-hatch. Ju­ve­niles mea­sure 16 to 18 mm in length after meta­mor­pho­sis. Ju­ve­nile males reach re­pro­duc­tive ma­tu­rity from 1 to 2 years post-meta­mor­pho­sis, whereas fe­males may not reach re­pro­duc­tive ma­tu­rity for 2 to 3 years post-meta­mor­pho­sis. Like all frogs, wood frogs ex­hibit in­de­ter­mi­nate growth. (Red­mer and Trauth, 2005)

• Development - Life Cycle
• metamorphosis
• indeterminate growth

Re­pro­duc­tion

Wood frogs ex­hibit "ex­plo­sive" breed­ing in late win­ter or early spring when the first warm rains occur. Frogs wake from hi­ber­na­tion and mi­grate to breed­ing ponds. In­di­vid­u­als show some site fi­delity year to year. Not much in­for­ma­tion is known re­gard­ing how males at­tract a mate. In an ex­plo­sive breed­ing sit­u­a­tion the suc­cess of the male in find­ing an avail­able and will­ing fe­male is strictly den­sity-de­pen­dent. (Red­mer and Trauth, 2005)

• Mating System
• polygynandrous (promiscuous)

Wood frogs are sea­sonal breed­ers that breed from early March to May. They are the first frogs to begin call­ing, often be­fore the ice is com­pletely off the breed­ing ponds. While the calls of these male frogs are very abun­dant in sea­son, once the breed­ing sea­son is over they be­come silent. Dur­ing the breed­ing sea­son how­ever, they cre­ate a cho­rus of duck-like quack­ing sounds, de­scribed by some as a "lot of chuck­ling". Once mate choice is ac­com­plished and am­plexus oc­curs, the fe­male will 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 grass, or they can be free stand­ing. After about a week or so the egg mass be­gins to flat­ten out, al­low­ing it to rest on the sur­face of the water. The jelly around the eggs be­comes green in color cre­at­ing a great cam­ou­flage. The green color of the jelly is due to the pres­ence of nu­mer­ous small green algae. The eggs hatch after 9 to 30 days and the tad­poles will un­dergo meta­mor­pho­sis when they are 2 months old. Male ju­ve­nile frogs reach re­pro­duc­tive ma­tu­rity when they are 1 to 2 years old, while fe­males take a bit longer and can­not re­pro­duce until they are 2 to 3 years old. (Co­nant and Collins, 1998; Red­mer and Trauth, 2005)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • external
• oviparous

• Breeding interval

  Wood frogs breed once yearly.

• Breeding season

  Wood frogs breed from March to May.

• Range number of offspring

  1000 to 3000

• Range time to hatching

  9 to 30 days

• Range age at sexual or reproductive maturity (female)

  2 to 3 years

• Range age at sexual or reproductive maturity (male)

  1 to 2 years

Like many frogs, wood frogs do not pro­vide any fur­ther parental care after fer­til­iz­ing and lay­ing the eggs. Eggs are sup­plied with a nu­tri­tious yolk sac to sus­tain the tad­poles dur­ing the early stages of life. The par­ents se­lect breed­ing sites with­out fish to in­crease the like­li­hood that their young will sur­vive. (Red­mer and Trauth, 2005)

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
  • protecting
    • female

Lifes­pan/Longevity

Wood frogs frogs are ex­pected to live to 4 or 5 years old for males and fe­males, re­spec­tively, liv­ing in Que­bec and south­ern Illi­nois. Stud­ies done in sev­eral other states showed wood frogs live to be 3 to 4 years old for males and fe­males, re­spec­tively. It is un­known why males con­sis­tently have shorter lifes­pans than fe­males. (Red­mer and Trauth, 2005)

• Typical lifespan
  Status: wild

  3 to 5 years

• Range lifespan
  Status: wild

  3 (high) years

  AnAge

Be­hav­ior

Wood frogs are a di­ur­nal species. These frogs per­form sea­sonal mi­gra­tions to breed­ing ponds in late win­ter or early spring. In­di­vid­ual wood frogs show sig­nif­i­cant breed­ing site fi­delity and will often mi­grate within the same area through­out their lives. Though they amass at breed­ing ponds, these frogs are mostly soli­tary.

Wood frog tad­poles have been shown to have the strongest pow­ers of kin recog­ni­tion yet dis­cov­ered in am­phib­ian lar­vae. These tad­poles can rec­og­nize kin using ma­ter­nal and pa­ter­nal fac­tors. They have been doc­u­mented (by mark­ing them with dye and re­leas­ing them into nat­ural habi­tats) to ag­gre­gate back to­gether. This may be a sur­vival mech­a­nism al­low­ing them the po­ten­tial ben­e­fit of food, ther­moreg­u­la­tion, and de­fense against preda­tors. (Blaustein and Walls, 1995; Red­mer and Trauth, 2005; Sav­age, 1961)

• Key Behaviors
• terricolous
• diurnal
• motile
• migratory
• hibernation
• solitary

Home Range

Wood frog ter­ri­tory size is cur­rently un­known. Home range for these frogs is es­ti­mated to be an av­er­age of 83.6 square me­ters. (Red­mer and Trauth, 2005)

Com­mu­ni­ca­tion and Per­cep­tion

Males ac­tively search for fe­males dur­ing the breed­ing sea­son; how­ever, they are un­able to tell males from fe­males by sight. Sex recog­ni­tion is ac­com­plished by the males em­brac­ing other frogs (re­gard­less of sex) and re­leas­ing those that are not fat enough to be fe­males full of eggs. If a male is em­braced he lets out a loud croak. A fe­male will also be let go if spawn­ing has al­ready oc­curred, be­cause of her thin body size. (Hard­ing, 1997)

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 use au­di­tory forms of com­mu­ni­ca­tion nearly ex­clu­sively dur­ing the breed­ing sea­son. (Hard­ing, 1997)

• Communication Channels
• visual
• tactile
• acoustic

• Perception Channels
• visual
• tactile
• acoustic

Food Habits

Adult wood frogs eat a va­ri­ety of ter­res­trial in­sects and other small in­ver­te­brates, es­pe­cially spi­ders (Order Araneae), bee­tles (Order Coleoptera), moth lar­vae (Order lep­i­doptera), slugs (Order Sty­lom­matophora) and snails (Order Sty­lom­matophora). Wood frog lar­vae con­sume algae, de­cay­ing plant and an­i­mal mat­ter, and eggs or lar­vae of other am­phib­ians. (Chenard, 1998; Hard­ing, 1997)

• Primary Diet
• carnivore
  • eats non-insect arthropods

• Animal Foods
• eggs
• carrion
• insects
• terrestrial non-insect arthropods
• mollusks
• terrestrial worms

• Plant Foods
• algae

Pre­da­tion

Adult wood frogs have many preda­tors in­clud­ing larger frogs, garter snakes, rib­bon snakes, water snakes, herons, rac­coons, skunks, and mink. Tad­poles are preyed upon by div­ing bee­tles, water bugs, and Am­bystoma sala­man­der lar­vae. Leeches, east­ern newts, and aquatic in­sects may eat wood frog eggs.

Wood frogs have de­vel­oped sev­eral anti-preda­tor mech­a­nisms. Older tad­poles de­velop poi­son glands that repel many preda­tors. Adult wood frogs have nox­ious skin se­cre­tions but they are only ef­fec­tive in de­ter­ring shrews. These frogs rely on their cryp­tic col­oration to cam­ou­flage into the for­est floor and es­cape preda­tors. If cap­tured, wood frogs may emit a pierc­ing cry that may star­tle the at­tacker enough to re­lease the frog. (Hard­ing, 1997)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • Garter snakes (genus Thamnophis)
  • Ribbon snakes (Thamnophis sauritus)
  • Northern water snakes (Nerodia sipedon)
  • Herons (Ardeidae family)
  • Raccoons (Procyon lotor)
  • Skunks (Mephitidae family)
  • American mink (Neovison vison)
  • Diving beetles
  • Water bugs
  • Salamander larvae (genus Ambystoma)
  • Leeches
  • Eastern newts (Notophthalmus viridescens)

Ecosys­tem Roles

Wood frogs have many preda­tors and thus pro­vide food for many an­i­mals in an ecosys­tem. They also feed on many ter­res­trial and aquatic in­ver­te­brates and there­fore con­trol in­sect pop­u­la­tions.

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Wood frogs, along with other am­phib­ians, are great in­di­ca­tors of en­vi­ron­men­tal health. Pop­u­la­tion de­clines in species of am­phib­ians should be of great con­cern. Wood frogs may also help to con­trol in­ver­te­brate pests.

• Positive Impacts
• research and education
• controls pest population

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are no known neg­a­tive ef­fects of wood frogs on hu­mans.

Con­ser­va­tion Sta­tus

The In­ter­na­tional Union for Con­ser­va­tion of Na­ture and Nat­ural Re­sources (IUCN) con­sider wood frogs to be of "Least Con­cern" as they are an abun­dant and wide­spread species. 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. Pop­u­la­tions may de­cline if breed­ing ponds are drained or for­est habi­tats are logged. Many mi­grat­ing frogs are killed while cross­ing busy roads to ac­cess breed­ing ponds. Stud­ies have shown that eggs and lar­vae may be harmed by acid rain or toxic runoff that enter breed­ing pools. (Hard­ing, 1997)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Other Com­ments

Wood frogs uti­lize a cryo­genic freez­ing process dur­ing hi­ber­na­tion. In the win­ter, as much as 35 to 45% of a frog's 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. (Red­mer and Trauth, 2005)

Con­trib­u­tors

Tanya Dewey (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor, George Ham­mond (ed­i­tor), An­i­mal Di­ver­sity Web Staff, Rachelle Ster­ling (ed­i­tor), Spe­cial Pro­jects.

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

Katie Kiehl (au­thor), Michi­gan State Uni­ver­sity, James Hard­ing (ed­i­tor), Michi­gan State Uni­ver­sity.

Ref­er­ences

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..

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

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.

Red­mer, M., S. Trauth. 2005. Am­phib­ian De­clines. Lon­don, Eng­land: Uni­ver­sity of Cal­i­for­nia Press, Ltd.

Sav­age, R. 1961. The Ecol­ogy and Life His­tory of the Com­mon Frog. Lon­don: Sir Isaac Pit­man and sons, LTD..