What’s Up with House Mice? – A Review GaryWitmerand SusanJojola USDAAPHISWildlifeServices,NationalWildlifeResearchCenter,FortCollins,Colorado ABSTRACT : Thehousemouseisprobablythemostwidespreadinvasivemammalianspecies,beingubiquitousworldwide.In commensal situations, they are known mainly for property damage, for consumption and contamination of stored foods, as a noise/sanitation/odornuisance,andasavectorofsomediseases.Insomefieldsettings,theyalsocauseconsiderabledamageto fieldcropsandtonaturalresources,suchaswhenintroducedtoislands.Werelyheavilyuponsanitation,rodent-proofing,capture devices, and rodenticides to control populations and reduce damage. However, a number of situations exist whereby these traditionalmethodsarenotadequateorappropriate:cropdamageduring“mouseplagues”inAustralia,livestockfeedconsumption andcontaminationanddiseasehazardsinpoultryandanimalfacilitiesintheU.S.,andnaturalresourcedamageonsmallislands.In thisreview,challengesandsomepotentialsolutionstohousemousemanagementarepresented,includinggeneticresistanceto anticoagulants,theeffectivenessofbaitsgivenabundantfoodresources,there-invasionproblemandneedforperimeterstrategies, efforts with fertility control, and the need for effective multi-capture trap devices. In difficult situations, an IPM strategy that incorporatesacombinationofmethodscloselyintegratedwithlandusesandmanagementpracticesisnecessary. KEY WORDS : commensalrodents,housemouse, Musdomesticus , Musmusculus ,rodentmanagement,rodenticides Proc.22nd Vertebr.PestConf. (R.M.TimmandJ.M.O’Brien,Eds.) PublishedatUniv.ofCalif.,Davis. 2006.Pp.124-130. INTRODUCTION lived (generally less than 1 year) and have high House mice ( Mus musculus and M. domesticus ) are populationturn-overrates;theyaretrulyan“r-selected” the most widespread mammalian species in the world, species. In one study, 20 mice placed in an outdoor nexttohumans.Housemiceoriginatedinthegrasslands enclosurewithabundantfood,water,andcover,becamea ofCentralAsiaandfollowedhumansaroundtheworld. populationof2,000in8months(Corrigan2001). Thereareanumberofspeciesinthegenus Mus ,butmost Miceareknowntosurviveandevenbreedundervery common around the world are Mus musculus and M. extremeconditions,includingdeepincoalmines,athigh domesticus .Here,weusethetermhousemousetorefer mountain elevations, and even in meat cold storage toboth,asthereisdebateintaxonomiccirclesastothe lockers.Althoughtheyevolvedasgrassandseedeaters, distinction between these two very similar species and micecanfeedonvirtuallyanything.Theycanusealmost whether or not they should be lumped under Mus anything for shelter and bedding. Mice are curious by musculus . In general, Musdomesticus isslightlylarger natureandareveryopportunistic,unlikethecommensal andmoreuniformlycolored(abufforgraybrown)than rats, which are much more neophobic. The abilities of M.musculus . The genusisdescribedin moredetailin micetoclimb,jump,swim,dig,gnaw,andaccesssmall Lund(1994)andNowak(1999). placesaretrulyremarkable.Micehavebeendocumented Therehasnotbeenareviewofhousemousebiology, tojumpabout46cmandtogetthroughholesonly6mm behavior, ecology, damage, and management in quite indiameter(Baker etal .1994). sometime.Inthisreview,werevisitthesetopics.We Housemicehavequiteabehavioralrepertoire.Over alsopointoutsomeofthedifferencesbetweenmiceand 50 individual behavior elements have been described, the commensal rats ( Rattus spp.). We examine some includingnon-socialbehaviors(suchasgrooming),social seriousproblemareasaroundtheworldinvolvinghouse investigation and sexual behaviors, and agonistic mice. Finally, we consider some management and behaviors (Mackintosh 1981). In fact, “behavioral researchneedsthatcouldenhanceourmanagementhouse flexibility”isconsideredkeytothesuccessofthehouse micepopulationsandthedamagetheycause. mouse as a species. As a result, house mice have complex,yetadjustablesocialsystems. ABILITIESANDVALUESOFHOUSEMICE In general, miceliveinextendedfamilyunitscalled House mice have remarkable abilities that have “demes”(LathamandMason2004).Thesizeofthearea allowedthemtobehighlysuccessfulincolonizingmost used by this group can vary greatly, depending upon of the world. Perhaps chief among these are their resourceavailabilityanddensities,fromafewmetersto reproductive potential and their adaptability. Several over100monaside.Micehaveastrongsenseoftouch notableresearchershave madeacareer ofstudyingthis and kinetic abilities that allow them to move rapidly in remarkable species (e.g., Berry 1970, Bronson 1979). total darkness and return home after extensive forays This small (±20 g) and highly prolific animal is a (Corrigan2001).Pheromonesplayanimportantrolein continuous breeder in many situations; a female can thisabilityandalsoareessentialinsocialinteractionand produce6-8litters,eachwith4-7young,peryear.The breeding activities. Mice are primarily crepuscular or young mature within 3 weeks or so, and they soon nocturnal, although this varies by density, resource become reproductively active. House mice are short- availability, and predatory pressures. Mice are very 124 active, perhaps as much as 50% of the time, although Finally, when introduced to islands, mice can cause much of this is entails grooming (Latham and Mason significant damage to natural resources, including both 2004). flora and fauna. For example, on Gough Island, mice Unlike commensal rats, mice are nibblers, eating feed on nestling albatross chicks (Cuthbert and Hilton smallbutfrequentmeals(Timm1994 a,Corrigan2001). 2004). Theycaneat10-20%oftheirbodyweightperday.Asa result, they pass 50 or more fecal pellets per day. The MANAGEMENTOFHOUSEMICE smalldroppingsininfestedbuildingsarea“trade-mark” POPULATIONSANDDAMAGE of their presence, even though they are rarely seen. Alargenumberofmethodsandmaterialshavebeen Unlikerats,micedonotrequirefreewaterandcanmeet developed to help solve house mouse problems. In their water needs through metabolism of solid foods. general, the use of multiple approaches and materials Theywilldrinkfreewater,however,ifitisavailable. (that is, employing an integrated pest management It is important to distinguish between “traditional” strategy) is more likely to reduce the problem to a commensal populations of house mice, which live in tolerablelevel.Thetoolsavailableandtheirproperuse closeassociationwithhumansandtheirhabitations,and have been reviewed by Prakash (1988), Timm (1994 a), feralpopulationsthattrulyliveofftheland.Feralmice and Corrigan (2001). Many technical guides are also typicallyhavelargerhomerangesandspendlesstimein available from Cooperative Extension Service offices, territorialdefenseandpatrollingtheirterritories(Latham private companies, and agricultural and health andMason2004).Theytendtobeseasonalbreedersand departments;manyoftheseareavailableontheInternet. exhibit large seasonal fluctuations in densities. They It seems that a major conference on rodent biology, prefer areas of dense ground cover and populations are ecology, and management is held somewhere in the drivenbyrainfallandseedfallpatterns.Housemicedo world every 5 years or so and a proceedings made not compete well with the commensal rats nor with available (e.g., Singleton et al . 2003). This is an established native rodent populations. Hence, feral indication of the continual problems rodents cause and mouse populations usually occur where this situation theneedforongoingresearchandadaptivemanagement. doesnotexist,suchasonagriculturallandsinAustralia Among the management techniques for house mice, andonislandswithfewornoterrestrialmammals.These making resources less available to mice is an essential situationsarediscussedinmoredetailbelow. first step. This is accomplished by good sanitation House mice play a number of important ecological practicesandbymakingbuildingsrodentproof(Baker et roles,suchasprovidingapreybaseforalargearrayof al . 1994). Recall, however, that keeping mice out of predacious animals cycling nutrients, and dispersing buildingsisarealchallengebecauseoftheirremarkable seedsandspores.Alsoimportantistheverylargeroleof abilities.Nonetheless,thesuccessofcommensalratsand housemiceinmedicalresearch.Theyhavebeenusedto mice in urban/suburban, industrial, and agricultural this purpose at least since the mid-1660s, and modern settingsislargelyattributabletothe vastharboragethat laboratory strains were developed in the early 1900s weprovideinthoseareas. (Lund1994).Arecentarticlein USATODAY (March6, Traps,especiallykilltraps,havebeenusedforalong 2006,p.13D)estimatedthatasmanyas25millionmice time to control unwanted mice. The history of mouse areusedinmedicalresearcheachyear. trap development was reviewed by Drummond (2003). Snaptrapsareveryeffectivebutnotalwayspracticalto DAMAGECAUSEDBYHOUSEMICE useonalargescale.Appropriatebaitingandplacement House mice cause many types of damage (Timm isveryimportantforhighcapturesuccess(Timm1994 a, 1994 a). A major concern is the consumption and Corrigan 2001). Live traps are mostly used for rodent contaminationofstoredfoods;ithasbeenestimatedthat research purposes but have become more popular with substantialamountsofstoredfoodsarelosteachyearin the public, many of whom are averse to killing pest this manner (LaVoie et al .1991). Where feral popula- animals.Morerecently,multiple-capturelivetrapshave tionsofmiceoccur,theydamagemanytypesofcropsin becomeavailable(Temme1980).Whenmicearetaken the field, especially corn, cereal grains, and legumes. elsewhere and released, however, they generally do not Mice also consume and contaminate large