i l l i n o i s frogs & toads - vetmed.illinois.edu · illustrations by mark sabaj, illinois...

PhotographsbyMichaelRedmer©. Frogsandtoadsarenotshowninequalproportiontoactualsize.

F rogs and toads are the most conspicuous members of a very

secretivegroupofanimalscalledamphibians.Frogsandtoadsare

wellknownfortheirmatingcallandlong,insect-catchingtongue.

They are excellent gauges of environmental health because of their close

contactwithaquatic,wetland,andterrestrial*environments.Theyhavemoist,

sensitive skin that allows chemicals in the environment topass into their

bodies.Furthermore,theireggslackahardshellsotheirdevelopingyoung

also aredirectly exposed to the environment.Thepuzzlingdisappearance

of some frog and toad species in remote, pristine parts of the world has

scientists concerned about overall planetaryhealth.

*see glossary

1. woodfrog, Rana sylvatica 2. northernleopardfrog,Rana pipiens 3. chorusfrogcomplex,Pseudacris triseriata-maculata* 4. Fowler’stoad,Bufo fowleri 5. greentreefrog,Hyla cinerea 6. greenfrog,Rana clamitans 7. springpeeper,Pseudacris crucifer 8. graytreefrogcomplex,Hyla chrysoscelis-versicolor* 9. cricketfrog,Acris crepitans10. southernleopardfrog,Rana sphenocephala11. Americantoad,Bufo americanus12. plainsleopardfrog,Rana blairi13. bullfrog,Rana catesbeiana14. easternspadefoot,Scaphiopus holbrookii15. easternnarrowmouthtoad,Gastrophryne carolinensis16. Illinoischorusfrog,Pseudacris streckeri illinoensis17. bird-voicedtreefrog,Hyla avivoca18. crawfishfrog,Rana areolata19. pickerelfrog,Rana palustris20. uplandchorusfrog,Pseudacris feriarum

This poster was made possible by:

Illinois Department of Natural Resources

Division of Education

Illinois Natural History Survey

Illinois State Museum

Illinois Department of Transportation

Text: Christopher Phillips (Illinois Natural History Survey)

Design: Illinois State Museum

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I l l i n o i s

Frogs & Toads

Key

* Both the western chorus frog, Pseudacris triseriata, and the boreal chorus frog, Pseudacris maculata, are found in Illinois. They are difficult to distinguish by their appearance, so they are represented by one image on this poster. The eastern gray treefrog, Hyla versicolor, and Cope’s gray treefrog, Hyla chrysoscelis, also are similar in appearance and are represented by one image.

Anatomy

Illustration from Smith, 1961

F rogsandtoadsaretheonlymembersofthePhylumChordata,ClassAmphibia,andOrderAnura.

Unliketadpoles,adultsdonothaveatail.Adultfrogsandtoadshaveasquatpostureandstrongrearlegs,

whichgivethemtheabilitytojumplongdistances.Theirlong,retractabletongueisusedtocatchtheir

mainfooditem,insects.

Thetympanicmembrane,ortympanum,aidstheprocessofhearing.Thiscircularstructure,locatedon

eachsideoftheheadbehindtheeyes,picksupvibrationsinairorwaterandpassesthemtotheinnerear.

Frogsandtoadsbreathethroughtheirlungslikemostterrestrialvertebrates,buttheyalsoutilizetheirsoft,

moistskinasasecondarymeansoftakinginoxygen.Thistypeofbreathingrequiresthattheskinbeboth

moistandpermeable.Theirskinremainspermeablebecausetheydonothaveaprotectivecoveringlikescales,

hair,orfeathers.Theymaintainmoisturethroughmucousglandsecretionsandbystayingnearwater.Toads

haveasomewhatmorewatertightskinthanfrogsandcanthereforeventurefartherfromwater.

Toadsarealsocharacterizedbythehornybumps,sometimescalledwarts,ontheirskin.Themostpro-

nouncedofthesebumps,calledparotoidglands,arefoundjustbehindthetoad’seyesandproduceapoison

thathelpsindefenseagainstpredators.Thepoisonrepelsanimalsaslargeasraccoonsbecauseofthemild

mouthdiscomforttheyexperiencewhentryingtoeatatoad.Oftentheydropthetoad,allowingitsescape.

Life History

Illustrations by Mark Sabaj, Illinois Natural History Survey

A ll Illinois frogs and toads have a complex, biphasic life cycle. Adults are aquatic, semi-aquatic, or

terrestrial,butallspecieslaytheireggsinwater.Duringthebreedingseason,whichmaystartasearlyas

FebruaryinIllinois,malescongregateatwetlandsandbeginchorusing.Themales’callsattractfemales

tothewetlands,andsoonmalesandfemalesarepairedinamplexus(1).Amplexusendswithfertilization:the

femaleexpelshereggsintothewater,andthemaleimmediatelycoversthemwithsperm.

Agelatinouscoatingusuallycoversanuraneggs(2),whichmaybelaidsingly,insheets,strings,orglobs,

dependingonthespecies.Somespecies’eggsareattachedtosticksorleaves;otherssimplyfloatfreelyinthe

water.Fertilizedeggsdevelopandhatchintofree-swimminglarvae,ortadpoles(3&4),withinafewdays.

Tadpoleshaveahorny,beaklikemouthdesignedforscrapingalgae,andtheybeginfeedingalmostimmedi-

atelyafterhatching.Afewweekslater,hindlimbsappear(5),andwithinamonthortwothetadpoleshave

undergonemetamorphosis.Exceptforatemporarytailstub,thenewlytransformedfrogletslookmuchlike

theadults.Theyusuallyleavethewaterandtakeupexistenceonlanduntilcoldweatherpromptsthemto

seekoutasafeplace,suchasthemuddybottomofapond,forhibernation.

Althoughthelarvaeareherbivorous,alladultfrogsandtoadsinIllinoisarecarnivorous.Themostcom-

monfooditemsareflyinginsects,suchasfliesandmosquitoes.Althoughadultsareprimarilynocturnal,they

maybeseenorheardduringtheday,especiallyiftheweatherisovercastorrainy.

Bibliography Agency ResourcesTheIllinoisDepartmentofNaturalResources(IDNR)offersavarietyofinformation

aboutfrogsandtoads.TheDivisionofFisheriesResourcesregulatestheharvestoffrogsfor

gamepurposes.TheIllinoisNaturalHistorySurveystudiesfrogandtoaddistributionsand

populationlevelsandmaintainsaresearchcollectionofanurans.TheIDNRDivisionof

Educationprovidesaquatic-relatededucationalmaterialsforteachers,includingtheAquatic

IllinoisandBiodiversity of Illinois,Volume I: Aquatic HabitatsCD-ROMs.Wetlandkitsfromthe

EducationSectionoftheIllinoisStateMuseumareavailableforloanatlocationsstatewide.

Illinois Department of Natural Resources

Illinois Natural History Survey1816SouthOakStreet

Champaign,IL61820

217-333-6880

http://www.inhs.uiuc.edu

Illinois State MuseumEducationSection

502SouthSpringStreet

Springfield,IL62706-5000

217-782-5993

http://museum.state.il.us

Division of EducationOneNaturalResourcesWay

Springfield,IL62702-1271

217-524-4126

http://dnr.state.il.us

dnr.teachkids@illinois.gov

Division of Fisheries ResourcesOneNaturalResourcesWay

Springfield,IL62702-1271

217-782-6424

http://dnr.state.il.us

Glossary

Amplexus thematingclaspoffrogsandtoads;themaleholdsthefemalefrombehindwithhisforelegsfirmlyaroundherchest

Anuran memberofthevertebrateorderAnura,characterizedbylackofatail,moistskin,andlonghindlegsadaptedforleaping:afrogortoad

Biphasic twodistinctphases;usuallyreferstoalifecyclethathasalandandawaterportion

Carnivorous havingadietthatincludesmainlyanimals

Dorsolateral Fold alineofraisedskinalongeachsideoftheback(seeAnatomyillustration)

Endocrine ductlessglandsandtheirregulatoryproducts

Heavy Metals potentiallypoisonousmetalssuchaslead,mercury,andcadmium

Herbivorous havingadietthatincludesmainlyplants

Larva (pl.larvae)thenewlyhatched,immatureformofananimalthatun-dergoesmetamorphosis,differingmarkedlyinformandappearancefromtheadult

Metamorphosis amarkedchangeintheformorstructureofananimaloccurringafterbirthorhatching

Mucous Gland Secretion clearwateryliquidthatissecretedontotheskinofamphibiansthroughsmallporesdistributedoverthebodysurface

Nocturnal activeprimarilyatnight

Parotoid Glands paired,wartlikeglandsintheskinoftoads;locatedbehindtheeyesorintheneckandshoulders

Snout-to-Vent Length thedistancefromthetipofthesnouttotheexcretoryopening;thestandardmeasurementforfrogsandtoads

Terrestrial landbased,orlivingonland

Tympanum (tympanicmembrane)theexternallyvisiblepartoftheeardruminmostfrogsandtoads(seeAnatomyillustration)

Vertebrate animalwithabackbone

Frog & Toad Facts Frogsandtoadsdonotcausewarts.

ThelargestIllinoisanuranisthebullfrog,Rana catesbeiana,whichcanattainasnout-to-ventlengthof15cm(6inches).

ThesmallestIllinoisanuranisthecricketfrog,Acris crepitans,whichaverages2cm(1inch)snout-to-ventlength.

Theaveragefrogcanleapadistanceequaltotentimesitsbodylength.

Mostburrowingfrogsdigwiththeirhindlegs,buttheIllinoischorusfrog,Pseudacris streckeri illinoensis,isoneofonlyafewburrowingspeciesthatdigswithitsfrontlegs.

Thedietoftheeasternnarrowmouthtoad,Gastrophryne carolinensis,consistsalmostexclusivelyofants.

Thelongtongueoffrogsandtoadsisfoldedinhalfwhenstoredinthemouth.Whenextendedforcapturingprey,thetongueunfoldsandis“flipped”outratherthanbeingcastoutstraight.

TheIllinoischorusfrog,Pseudacris streckeri illinoensis,canhuntforfoodwhileitisunderground.Itprobablyeatsavarietyofinsectlarvae,suchascutworms(mothlarvae),thatitfindsinitssandyburrows.

Bullfrogs,Rana catesbeiana,arefamousfortheirincredibleeatinghabits.Theywillattempttoeatanythingthatmoves—thattheycanatleastpartiallyswallow.Theyhavebeenknowntoeatbabyducks,smallmammals,otherbullfrogs,andsnakes.

ThetreefrogsofIllinoishaveastickycupattheendofeachtoethatallowsthemtoclimbverticalsurfacessuchaswindowsandtreetrunks.Treefrogsmaybefoundinbranchesmorethanfiftyfeetofftheground.

Afemalebullfrog,Rana catesbeiana,canlayover20,000eggsinathinfilmmeasuringtwofeetbytwofeet.

SomeIllinoisfrogs,suchasthewoodfrog,Rana sylvatica,accumulateglycerolintheirbodytissues.Theglycerolactsasanantifreeze,allowingthemtosurvivesubfreezingtemperatures.

Frog CallsAnimalsproducesoundsforavarietyofreasons,

but the primary function of vocalization is

announcing the presence of one individual

toothersof the same species.Frogs and toadshave

well-developedvoicesthatareusedtoattractmates,

proclaimfeedingterritories,andsignalalarm.Ofthese

functions,thematingcallsofthemalesareprobably

themostfamiliartous.Justasinbirds,eachspecies

offrogortoadhasauniquematingsong,andbiolo-

gistscanidentifyanindividualspeciesbyitscallalone.

Anuransproducesoundsinamannersimilartothat

ofmostothervertebrates,bypassingairoverthevocal

cords.Frogsandtoadstaketheprocessastepfurtherby

usingthevocalsac—looseskinusuallylocatedunder

thelowerjaw—toresonateoramplifythesound.Both

malesandfemalespossessfunctionalvocalcords,but

theyarebetterdevelopedinmales.Onlymaleshave

vocalsacs,whichaccountsforthedifferenceinsound

productionbetweenthesexes.

Frog calls can be “described” in scientific terms

byplayingarecordingofacallthroughanelectronic

sound analyzer.The resulting graph, called a sono-

gram,isavisualrepresentationofthecall.Scientists

usesonogramstoidentifyspecieswhosecallscannot

bedistinguishedwiththehumanear.Forthisreason,

sonogramsareusedtodistinguishbetweenthetwospeciesofgraytreefrogthatoccurinIllinois.Theeastern

graytreefrog,Hyla versicolor,andCope’sgraytreefrog,Hyla chrysoscelis,areidenticalinoutwardappearance

andwereconsideredtobeofthesamespeciesuntilbiologistsdetecteddifferencesintheirmatingcalls.So-

nogramsofthetwomatingcallsshowthatthecallofCope’sgraytreefroghasahigherpitchandmorepulses

persecondthanthatoftheeasterngraytreefrog.However,thedifferencesthatappearobviousinthesound

analysisareactuallyverysubtleinnatureandcanbepickeduponlybyatrainedear.

I l l i n o i s

Frogs&

Toads

Behler,J.L.,andF.W.King.1979.The Audubon Society field guide to North American reptiles and amphibians.AlfredA.Knopf,NewYork.719pp.

Conant,R.,andJ.T.Collins.1991.Reptiles and amphibians of eastern/central North America.HoughtonMifflinCompany,Boston.450pp.

Dickerson,M.C.1907.The frog book: North American toads and frogs with a study of the habits and life histories of those of the northeastern United States.Doubleday,PageandCo.,NewYork.253pp.

Duellman,W.E.,andL.Treub.1986. Biology of amphibians.McGraw-Hill,Inc.,NewYork.670pp.

Halliday,T.,andK.Adler(editors).1986.The encyclopedia of reptiles and amphibians.FactsonFileInc.,NewYork.143pp.

Herkert,J.R.,editor.1992.Endangered and threatened species of Illinois: Status and distribution.Vol.2,Animals.IllinoisEndangeredSpeciesProtectionBoard,Springfield.142pp.

Johnson,T.R.2000.The amphibians and reptiles of Missouri.DepartmentofConservation,JeffersonCity,Missouri.400pp.

Parmalee,P.A.1954. Amphibians of Illinois.StoryofIllinois,no.10.IllinoisStateMuseum,Springfield.38pp.

Phillips,C.A.,R.A.Brandon,andE.O.Moll.1999.Field guide to amphibians and reptiles of Illinois.IllinoisDepartmentofNaturalResources,IllinoisNaturalHistorySurvey,Champaign,Illinois.Manual8.282pp.

Smith,P.W.1961.The amphibians and reptiles of Illinois.IllinoisNaturalHistorySurveyBulletin 28:1298.

Vogt,R.C.1981.Natural history of the amphibians and reptiles of Wisconsin.TheMilwaukeePublicMuseum,Milwaukee.205pp.

Wright,A.H.,andA.A.Wright.1949.Handbook of frogs and toads.ComstockPublishingCo.,Ithaca,NewYork.640pp.

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eastern gray treefrog

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Cope’s gray treefrog

The vertical axis (y) represents the pitch, and the horizontal

axis (x) represents time, usually seconds.

DORSOLATERAL FOLD

EYELID

EYE

TYMPANUM

FOOT

TARSUS

TIBIA

FEMUR

Conservation

Cricket frog (Acris crepitans), from Slime, Scales and Mudpuppy Tails, 1997,

Illinois Department of Natural Resources, Office of Public Services, Division

of Education, Springfield

O verthelastfewyearstherehasbeenincreasedconcernaboutworldwidepopulationdeclines

andevenextinctionsoffrogandtoadspecies.Habitatdestructionanddegradationareclearly

responsibleinsomecases,butthemostalarmingdeclineshaveoccurredinrelativelypristine

environmentssuchastherainforestsofeasternAustraliaandthecloudforestsofCostaRica.Closerto

home,biologistsintheupperMidwesthavebeennoticingthedisappearanceofoursmallestfrog,the

cricketfrog(Acris crepitans).Untiltheearly1980s,cricketfrogswereamongthemostcommonanurans

inIllinois,andtheycouldbefoundinalmosteverycounty.Recently,biologistshavenoticedadeclinein

thenumberofcricketfrogpopulationsintheChicagoregionbutnotdownstate.Amongthecausesthat

havebeensuggestedforthisdeclineisbuild-upoftoxicsubstances(pesticides,heavymetals)inthefrogs’

breedingponds,leadingtoendocrinedisruption.AsurveyofmuseumspecimenscollectedinIllinoisover

thepast100yearsshowedthatmorefrogsfromtheChicagoregiondisplayedanatomicalsignsofendocrine

disruptioncomparedtotherestofthestate.IntheheavilyindustrialandurbanlandscapeoftheChicago

region,habitatdestructionandfragmentationarealsolikelyinvolved.

Equal opportunity to participate in programs of the Illinois Department of Natural Resources (IDNR) and those funded by the U.S. Fish and Wildlife Service and other agencies is available to all individuals regardless of race, sex, national origin, disability, age, religion or other non-merit factors. If you believe you have been discriminated against, contact the funding source’s civil rights office and/or the Equal Employment Opportunity Officer, IDNR, One Natural Resources Way, Springfield, IL 62702-1271; 217/785-0067; TTY 217/782-9175. This information may be provided in an alternative format if required. Contact the DNR Clearinghouse at 217/782-7498 for assistance.

Printed by the Authority of the State of Illinois IISG 08-674 10M 03/08

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