Haveyoueverwonderedwhatthenaturalworldofmeadows,flowers,grassandtreesmustlooklikeseenthroughthefacetedcompoundeyesofahoneybeeorabumblebee?Dotheyseeincolor?Ifso,whatcolorsdotheyseeandaretheydifferentfromtheportionsofthespectrumthathumaneyesaretunedinon?Dotheyperceivemotionthesameaswedo?Cantheyseecolorsorperceivevisualattributesofobjectstowhichweareblind?
If,likeme,youhaveoftenwonderedwhatitwouldliketobea"beeforaday"orjustforafewminutes,then,thisshortnarrativemaybegintoanswersomeoftheseintriguingquestionsforyou.So,comejoinwithusatTheBeeWorksandexperiencethealienvisionsensoryworldofhoneybees.Let'stakethatimaginaryjourneynowandpretendtoseetheworldthroughtheuniqueeyesofabeeforjustafewminutes...
Workerhoneybeeshaveeyesthataredividedupintotwogreatellipsesonoppositesidesoftheirhead.Eachcompoundeyeismadeupofabout6,900individualunits/facetspackedtightlytogetherashexagonsandknownasommatidia.Eachommatidiumisabletocapturelightraysfromasmallangleofview.Theseraysarefocusedbyseverallensesontolightsensitivepigment.Oncestimulated,thesesensorycellspassalongnervousimpulsescodinginformationonthequalityofthelight(itswavelength=visiblecolorandplaneofpolarization)totheopticnerveswhicheventuallyreachtheopticlobesofthehoneybees'brain.
Howmanyeyesdoyouthinkabeehas?Twoyousay?No,actually,beeshavefiveeyesinall.No,thisisn'tatrickquestion.Ontopoftheirheadarethreesimpleeyes,knownasocelli,arrangedinatriangularpattern.Thesesimpleeyeswithasinglelensarebestforinformingthebeeofchangesinlightintensity.Theseocellihelpthemnavigatearoundflowersandgettingtoandfromthenestatdawnanddusk.
Honeybeesarealsoextremelysensitivetorapidmovements.Thishasbeencalledtheirflickerfusionpotential.Toabeeflyingat15mphlowoverafloweringmeadow,theflowersmusttwinkleonandofflikestarsinthenightsky.Theanalogyisoftenmadethatifyouputabeeinatheater,themovingfilm(goingbyatamere16or24framespersecond)wouldbeseenasdistinctstillimagesbythebees.Youwouldhavetogreatlyspeedupthatsamefilmtoachievethemotioneffectforabeemoviegoer.Theyalsohaveotherseeminglymysteriousandcertainalienvisualabilitiesbeyondourown.Forexample,beescandetecttheplaneofpolarizationoflightinthesky.Thisallowsthemtodetectthepositionofthesunevenonanovercasedaywhenthereisonlyapatchofblueinthesky.Thatway,theycanfindtheirwaytoandfromvariouspatchesofflowersandreturnbackhomesafelywithoutgettinglost.
Thecolorsenseofhoneybees(andotherbees)wasonlyguessedaboutuntilthiscentury.BiologistssinceC.K.Sprengel(1793)hadlongbelievedthatflowersacquiredtheircolorsas"livingbillboards"toadvertisetheirpresencetopasserbyinsectswhowould,inturn,movetheirpollengrainsfromflowertoflower--resultinginfruitandseedsetforthefloweringplants.Sprengelevencalledthemarkingsonsomecolorfulflowers"saftmale"(inGerman),sapsignsinEnglishtonotethattheywerelandingandorientationguidesforflower-visitinginsects.Bybeingcolorful,theythought,itwouldbeeasierforfloralinsectvisitorstoseethesmallflowerssetagainstthegreenorbrownbackdropofmostenvironments.Ifbeesandotherinsectscouldseeandfindthemeasily,thatwouldallowthemtomoveamongsttheblossomsfasterthusincreasingtheirefficiencyaspollinators.
Infact,honeybeeswerethoughttobecolorblinduntilthepioneeringexperimentalresearchofthelateDr.KarlvonFrischinGermanyduringthetheearlypartofthiscentury.Heprovedthattheydoinfacthavethreecolor(trichromatic)visioninmanyrespectslikeourownvisualsystem.KarlvonFrischwasabletodemonstratethatbeeshadcolorvisionbytrainingthemtoalittledishofscentedsugarwater(theirsweetreward)setuponabluesquareofpaper.Byrandomlyplacingthisbluesquareinabig"checkerboard"ofgraysquares,hecouldtellthatthebeesactuallysawandrecognized/learnedwherethebluesquarewaspositioned.Theyweren'tjustrelyingupontherelativeintensityofthesquares.Thistrainingtechniquehasbecomethestandardformanybeebehavioralexperimentsuptothepresentday.
Althoughbothhoneybeesandpeoplehaveavisualsystembaseduponthree-colors,thelimitsofthiscolorsensitivityareverydifferent.PeoplecannotseeveryfarintotheVioletorUltravioletregionoftheelectromagneticvisualspectrum.Weareessentiallyblindtowavelengthsoflightbelow400nanometers/millimicrons(lightinthisregionsiscalledUV-AandUV-Blight).Thesearethepowerfullightrayswhichcauseustotanorsunburn.Beescanseetheseinvisible-to-usraysoflight!Anotherinterestingdifferencehappensattheoppositeendofthevisiblespectrum.Wecaneasilyseethecolorofaredsweaterorredfireengine(atleastmanyofthemusedtobered!).Toahoneybee,however,thecolorredisinvisible.Theyseeredobjectsasblack,ortheabsenceofcolor.Sharethiswithyourfriendsatschool,yourteachersandparents.Didtheyknowthatbeesarenotcolorblindandthattheycansee"secret"colorsthatwecannot?
Inthephotographtotheleftweseeanarrayofflowersastheyappeartopeoplewhomightbeadmiringtheminadisplaycasewithinafloristshop.Noticethattheyoccurinmanydifferentshapesandsizeswithvarioussubtlecolormarkingsontheirpetals.Thecolorsofflowersaresaidbyphysiciststobehighlysaturated.Thatmakesthemverynoticeablewhencomparedtootherless-saturatedcoloredobjectsinthenaturalenvironment.*ThesemagnificientphotographsappearycourtesyofDr.RandolfMenzel(Berlin,Germany).SeethereferencetothepublicationwheretheyappearbelowintheSuggestedReadingssection.
Thecollectionof10photographstotherightshowwhatthesameflowerswouldlookliketoapassinghoneybee.Noticethatthephotosaredarkblue/black.Theseweretakenbyusingaspecialultraviolet-transmittingfilterdescribedbelow.Althoughwedon'treallyknowexactlyhowthebeeseyesseethepatterns(andtheirbrainsinterprettheseneurosignals)wedoknowthatthesehiddenUVcolorsdostimulatethebeesvisionandtellthemwheretofindthefloralrewards(nectarandpollen)insidetheflowers.
Toseethesesameflowersasabeewould,wesimplyplaceavisiblelight-blockingfilteroverthecameralens(orVHScamcorder).Thisdark,almostblack,UVfilteronlyallowsultravioletlettopassthrough.Thisistheoppositefilterfroma"skylightorhaze"filterthatmanyamateurphotographersknowabout.WatchforanupcommingissueofGEARSinwhichwe'lltellyouhowtotakeyourownphotographsofhiddenUVfloralpatternsoncertainflowersandbutterfliesforlessthan$50.NoticeintheaboveUVphotographthattheflowerslookentirelydifferent.Manyflowerslookdark(allUVabsorbing)whenviewedunderultravioletlightasabeewouldseethem.Others(likesomesunflowersorblack-eyedSusans)haveacharacteristiccentralUV-absorbingbullseyepattern.Suchflowersappearaswhattheinsectphysiologistshavetermedbeepurple(thecombinationofyellow+UV).TheoutermostpartofthesunflowerraypetalsreflectyellowlightplusUVgivingthemthisbees'purplecolor.Wedon'tknowexactlywhatthaycolormightlookliketoahungryhoneybeeforager.ThecentralportionabsorbsUVsowouldsimplybewhatevercolor(brownish)istherealone.
Thereismuchmoretothestoryofhowbeeeyesworkandhowtheyperceivethecolorfulandvariednaturalandmanmadeworldaroundthem.Gotoyourlocalschoolorpubliclibraryandcheckoutabookonhoneybees.Trytodiscoverforyourselfsomeofthefascinatingthingsthatbeebiologists,entomologistsandbotanistshavefoundaboutthesecretlifeofthebeesandtheirworld.
SuggestedReadings--
⑴Frisch,Karlvon.1971.Bees:TheirVision,ChemicalSenses,andLanguage.RevisedEdition.CornellUniversityPress,Ithaca,NewYork,157pages.*Easytoreadandunderstandaccountforanyone.湖北天马养蜂场，加我们的微信一起学养蜂。
⑵Menzel,Randolf.1990.ColorVisioninFlowerVisitingInsects.InstitutFurNeurobiologieDerFreienUniversitatBerlin,pages3-16.Prof.Dr.RandolfMenzel,InstitutfurNeurobiologiederFreienUniversitatBerline,Konigin-Luise-StraBe28-30,1,000Berlin33,RepublicofGermany.*Technicalarticle,maybedifficultforstudentslessthanHighSchoolorCollege/Universityage.
⑶Menzel,R.andBackhaus,W.1990.Colorvisionininsects:In:VisionandVisualdysfunctionVol.6(Ed.P.Gouras),chapter15,MacMillanPress,Houndsville.*Again,atechnicalarticle,thisonebestsuitedforcollege-agedstudents.