Lithobates catesbeianusAmerican Bullfrog

Ge­o­graphic Range

North Amer­i­can bull­frogs (Litho­bates cates­beianus) are only na­tive to the Nearc­tic re­gion. They are found from Nova Sco­tia to cen­tral Florida, from the East coast to Wis­con­sin, and across the Great Plains to the Rock­ies. The nat­ural west­ern lim­its of this species are now con­fused due to their in­tro­duc­tion into places as far west as Cal­i­for­nia and Mex­ico. It is known that bull­frogs were in­tro­duced to areas of Cal­i­for­nia and Col­orado in the early 1900's. The species has also been in­tro­duced (ac­ci­den­tally or on pur­pose) into south­ern Eu­rope, South Amer­ica, and Asia.

Habi­tat

North Amer­i­can bull­frogs must live in water and are there­fore usu­ally found near some source of water, such as a lake, pond, river, or bog. Warm, still, shal­low wa­ters are pre­ferred. Bull­frogs are be­com­ing in­creas­ingly com­mon in areas that have been mod­i­fied by hu­mans. In­creased water tem­per­a­tures and in­creased aquatic veg­e­ta­tion, which are com­mon fac­tors of lakes pol­luted by hu­mans, favor bull­frogs by pro­vid­ing suit­able habi­tats for growth, re­pro­duc­tion, and es­cape from preda­tors.

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Phys­i­cal De­scrip­tion

North Amer­i­can bull­frogs are the largest true frog found in North Amer­ica, weigh­ing up to 0.5 kg and 203 mm in length. Typ­i­cal length ranges from 90 to 152 mm. Color varies from brown­ish to shades of green, often with spots or blotches of a darker color about the back. The hind feet are fully webbed. The sex of an adult bull­frog can be eas­ily de­ter­mined by ex­am­in­ing the size of the tym­pa­num (the ex­ter­nal ear of the frog) rel­a­tive to that of the eye. The tym­pa­num is a round cir­cle lo­cated on the side of the head near the eye, and in males it is much larger than the eye. In fe­males the tym­pa­num is as large or smaller than the eye. Also, dur­ing the breed­ing sea­son the throat of the male bull­frog is yel­low, whereas the fe­male's is white.

  • Sexual Dimorphism
  • sexes shaped differently
  • Range mass
    0.5 (high) kg
    1.10 (high) lb
  • Range length
    460 (high) mm
    18.11 (high) in
  • Average length
    100-175 mm
    in
  • Average basal metabolic rate
    0.0134 W
    AnAge

De­vel­op­ment

About four days after fer­til­iza­tion, spot­ted tad­poles emerge from the float­ing egg mass. The tad­poles have gills and a tail, which even­tu­ally dis­ap­pears as the tad­pole trans­forms into a froglet. Tad­pole de­vel­op­ment is quite slow; it may take be­tween one to three years to begin trans­for­ma­tion from the tad­pole stage into the adult stage. Adults reach sex­ual ma­tu­rity after an ad­di­tional two years.

Re­pro­duc­tion

Breed­ing takes place in May to July in the north, and from Feb­ru­ary to Oc­to­ber in the south. Fer­til­iza­tion is ex­ter­nal, with the fe­males de­posit­ing as many as 20,000 eggs in a foamy film in quiet, pro­tected wa­ters. Fer­til­iza­tion is usu­ally, but not al­ways, by one male. Tad­poles emerge about four days after fer­til­iza­tion. These tad­poles may re­main in the tad­pole stage for al­most 3 years be­fore trans­form­ing into frogs. Adults reach sex­ual ma­tu­rity after 3 to 5 years.

  • Breeding interval
    Bullfrogs breed once each year.
  • Breeding season
    May to July in the north and February to October in the south
  • Range number of offspring
    20000 (high)
  • Average time to hatching
    4 days
  • Range age at sexual or reproductive maturity (female)
    3 to 5 years
  • Range age at sexual or reproductive maturity (male)
    3 to 5 years

Fe­males pro­vide the eggs with yolk be­fore they are laid. There is no parental in­volve­ment in off­spring after the eggs are laid. Newly hatched tad­poles can take care of them­selves right away.

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

Lifes­pan/Longevity

The av­er­age bull­frog lives seven to nine years in the wild. The record lifes­pan of an an­i­mal in cap­tiv­ity is 16 years.

Be­hav­ior

North Amer­i­can bull­frogs pre­fer warm weather and will hi­ber­nate dur­ing cold weather. A bull­frog may bury it­self in mud and con­struct a small cave-like struc­ture for the win­ter. Their hunt­ing style is 'sit and wait.' Bull­frogs can wait for a long time for some type of prey to come by, then, with a flash of the tongue, they grab it and bring it back into their mouths. Bull­frogs are ac­tive both dur­ing the day and at night; they are most ac­tive when the weather is moist and warm.

Home Range

Adult males are very ag­gres­sive and de­fend their ter­ri­to­ries, which can range from 3 to 25 me­ters of shore­line, by phys­i­cally wrestling with oth­ers.

Com­mu­ni­ca­tion and Per­cep­tion

The call of a male bull­frog has a low fre­quency and can be heard for over one kilo­me­ter. The sound is often de­scribed as a low rum­bling "jug-o-rum". Bull­frogs also have a good sense of vi­sion and sense vi­bra­tions. See a video of a bull­frog call­ing here: http://​www.​midwestfrogs.​com/​.

Food Habits

Bull­frogs are preda­tors. They usu­ally eat snakes, worms, in­sects, crus­taceans, frogs, tad­poles, and aquatic eggs of fish, frogs, in­sects, or sala­man­ders. They are can­ni­bal­is­tic and will not hes­i­tate to eat their own kind. There have also been a few cases re­ported of bull­frogs eat­ing bats. Bull­frog tad­poles mostly graze on aquatic plants.

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

Pre­da­tion

Hu­mans hunt bull­frogs for frog legs, but they have a lim­ited hunt­ing sea­son in most states. Bull­frogs are also eaten by a wide va­ri­ety of other an­i­mals, de­pend­ing on the re­gion. These in­clude herons, such as great blue herons and great egrets, tur­tles, water snakes, rac­coons, and belted king­fish­ers. Most fish are averse to eat­ing bull­frog tad­poles be­cause of their un­de­sir­able taste.

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

North Amer­i­can bull­frogs help to con­trol in­sect pests. They are im­por­tant for med­ical re­search be­cause their skele­tal, mus­cle, di­ges­tive, and ner­vous sys­tems are sim­i­lar to those of other an­i­mals. They are often hunted for meat (frog legs).

  • Positive Impacts
  • food
  • research and education
  • controls pest population

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

In­tro­duced bull­frogs may be dri­ving na­tive frogs to ex­tinc­tion in some areas. Col­orado, among many other places, is ex­pe­ri­enc­ing prob­lems due to the in­tro­duced bull­frog pop­u­la­tion. Bull­frogs may have been in­tro­duced ac­ci­den­tally to trout streams and lakes dur­ing the Col­orado Di­vi­sions of Wildlife fish stock­ing op­er­a­tions. Bull­frogs oc­ca­sion­ally in­vade fish hatch­ery ponds and their lar­vae are caught along with the fishes that are rou­tinely stocked in ponds.

Con­ser­va­tion Sta­tus

Bull­frogs do well with changes in the en­vi­ron­ment that have oc­cured due to human mod­i­fi­ca­tion, and are be­com­ing in­creas­ingly com­mon in areas mod­i­fied by hu­mans. Bull­frogs have a much higher crit­i­cal ther­mal max­i­mum than most other frogs, mean­ing that they are able to thrive in higher water tem­per­a­tures. Bull­frogs have a longer breed­ing sea­son and a higher rate of pre-meta­mor­phic sur­vivor­ship, which also al­lows them to be more suc­cess­ful than other frogs. In some areas, such as Cal­i­for­nia, bull­frogs are dri­ving other frog pop­u­la­tions to ex­tinc­tion. One pos­si­ble rea­son to ex­plain why bull­frogs in Cal­i­for­nia might have an ad­van­tage over other species na­tive to that state is that bull­frogs evolved with a di­verse preda­tory fish fauna in east­ern North Amer­ica. In Cal­i­for­nia there have been at­tempts to con­trol bull­frog pop­u­la­tions by in­tro­duc­ing new fish species that are their preda­tors. Bull­frogs have evolved mech­a­nisms to avoid pre­da­tion by fish, such as less palat­able eggs and tad­poles, and tad­poles that are not ac­tive much of the time, which re­duces their ex­po­sure to preda­tors. Na­tive frog species of Cal­i­for­nia are also suf­fer­ing a de­cline be­cause bull­frogs are ef­fi­cient preda­tors of frogs and tad­poles.

Other Com­ments

Bull­frogs are well known for their enor­mous legs. They are some of the best jumpers in the world and are used in frog rac­ing in some parts of the United States.

Con­trib­u­tors

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

San­dra Bru­en­ing (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Cyn­thia Sims Parr (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor.

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

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

chemical

uses smells or other chemicals to communicate

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.

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

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.

introduced

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

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

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

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

sedentary

remains in the same area

sexual

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

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).

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

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

Ref­er­ences

"Frog­ging Abounds!!!" 1997. http://​www.​zoo.​utoronto.​ca/​-natalie/​frogpage.​html

"Michi­gan Frogs & Toads." 1997. http://​imc.​lisd.​k12.​mi.​us/​frog/​frogs.​html

"Rep­re­sen­ta­tive Species- Cana­dian Great Lakes Frogs and Toads." 1997. En­vi­ron­ment Canada. http://​www.​cciw.​ca/​glimr/​data.​habitat-rehabilitation/​hab43a.​html.​

"Med­ical Her­petol­ogy- The Med­ical and Eco­nomic Im­por­tance of Am­phib­ians and Rep­tiles." . 1997. http://​www.​worldcorp.​com/​biodiversity/​newsletter/​two/​herp.​htm.​

"Frog." 1994. Mi­crosoft En­carta. Com­puter soft­ware. Mi­crosoft.

Co­nant, Roger. 1975. A Field Guide to Rep­tiles and Am­phib­ians of East­ern and Cen­tral Amer­ica. Houghton Mif­flin Com­pany, Boston.

Ham­mer­son, G. A. 1982. Bull frog elim­i­nat­ing leop­ard frogs in Col­orado? Her­peto­log­i­cal Re­view 13(4): 115-116.

Ryan, M. J. 1980. The re­pro­duc­tive be­hav­ior of the bull­frog (Rana cates­beiana). Copeia (1): 108-114.

Cleve­land Mu­seum of Nat­ural His­tory, 2007. "Bull­frog (Rana cates­beiana)" (On-line). Frogs and Toads of Ohio. Ac­cessed Feb­ru­ary 21, 2007 at http://​www.​cmnh.​org/​site/​ResearchandCollections_​VertebrateZoology_​Research_​FamilyRanidae_​Bullfrog.​aspx.

Govin­dara­julu, P. 2000. "Sur­vey of Bull­frogs Rana cates­beiana in British Co­lum­bia" (On-line). Ac­cessed 1 Sep­tem­ber 2000 at http://​web.​uvic.​ca/​bullfrogs/​.

Ravenswood Media, Inc., 2005. "Frog calls . . . an evolv­ing "we­bu­men­tary"" (On-line). Ac­cessed July 05, 2005 at http://​www.​midwestfrogs.​com/​.