B-31

HOUSE MICE

Damage Prevention andControl Methods

Exclusion

Seal all openings larger than 1/4 inch(0.6 cm) wide.

Habitat Modification

Good sanitation practices reducesources of food, water, and shelter.

Store foodstuffs in rodent-proofstructures or containers.

Control weeds and remove debrisfrom around structures.

Frightening

Ultrasonic devices have not beenproven to control mice.

Repellents

Ro-pel®

Moth flakes (naphthalene) notspecifically registered, but may beof some value.

Toxicants

Anticoagulant rodenticides (slow-acting chronic-type toxicants).Brodifacoum (Talon®).Bromadiolone (Maki®, Contrac®).Chlorophacinone (RoZol®).Diphacinone (Ditrac®).Pindone (Pival®, Pivalyn®).Warfarin (Final® and others).

Toxicants other than anticoagulants(may be acute or chronic poisons).Bromethalin (Assault®, Vengeance®).Cholecalciferol (Quintox®).Zinc phosphide (Ridall Zinc®, ZP®).

Fumigants

Practical use is limited to structures,containers, and commodities; foruse only by trained personnel.

Trapping

Snap traps.

Live traps (Sherman-type, Ketch-All®,Tin Cat®, and others).

Glue boards.

Other Methods

Predators: dogs and cats are of limitedvalue in some situations.

Robert M. TimmSuperintendent and Extension

Wildlife SpecialistHopland Research & Extension CenterUniversity of CaliforniaHopland, California 95449

Fig. 1. House mouse, Mus musculus

PREVENTION AND CONTROL OF WILDLIFE DAMAGE — 1994

Cooperative Extension DivisionInstitute of Agriculture and Natural ResourcesUniversity of Nebraska - Lincoln

United States Department of AgricultureAnimal and Plant Health Inspection ServiceAnimal Damage Control

Great Plains Agricultural CouncilWildlife Committee

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Identification

The house mouse (Mus musculus, Fig.1) is a small, slender rodent that has aslightly pointed nose; small, black,somewhat protruding eyes; large,sparsely haired ears; and a nearlyhairless tail with obvious scale rings.House mice are considered among themost troublesome and economicallyimportant rodents in the United States.

Adult house mice weigh about 2/5 to4/5 ounce (11 to 22 grams). They aregenerally grayish brown with a gray orbuff belly. Similar mice include thewhite-footed mice and jumping mice(which have a white belly), andharvest mice (which have groovedupper incisor teeth). For more detailson species identification, see a fieldguide such as that by Burt andGrossenheider (1976).

Native to central Asia, this speciesarrived in North America with settlersfrom Europe and from other points oforigin. A very adaptable species, thehouse mouse often lives in closeassociation with humans and thereforeis termed one of the “commensal”rodents along with Norway and roofrats. House mice are much morecommon in residences and commercialstructures than are rats. Brooks (1973)regards them to be the most commonmammal in cities, next to humans.

Range

Following their arrival on colonists’ships, house mice spread acrossNorth America and are now found inevery state, including coastal areas ofAlaska, and in the southern parts ofCanada.

Habitat

House mice live in and around homes,farms, commercial establishments, andin open fields and agricultural lands.At times they may be found living farfrom human settlements, particularlywhere climates are moderate. Theonset of cold weather each fall intemperate regions may cause mice to

move into structures in search ofshelter and food.

Food Habits

House mice eat many types of foodbut prefer seeds and grain. They arenot hesitant to eat new foods and areconsidered “nibblers,” sampling manykinds of items that may exist in theirenvironment. Foods high in fat, pro-tein, or sugar may be preferred evenwhen grain and seed are present. Suchitems include bacon, chocolate candies,butter, and nutmeats.

Unlike Norway and roof rats, housemice can survive with little or no freewater, although they readily drinkwater when it is available. They obtaintheir water from the food they eat. Anabsence of liquid water or food ofadequate moisture content in theirenvironment may reduce their breed-ing potential.

General Biology,Reproduction, andBehavior

House mice are mainly nocturnal,although at some locations consider-able daytime activity may be seen. See-ing mice during daylight hours doesnot necessarily mean that a high popu-lation is present, although this is usu-ally true for rats.

Mice have poor eyesight, relying ontheir hearing and their excellent sensesof smell, taste, and touch. They areconsidered color-blind; therefore, forsafety reasons, baits can be dyed dis-tinctive colors without causing avoid-ance by mice, as long as the dye doesnot have an objectionable taste orodor.

House mice may burrow into theground in fields or around structureswhen other shelter is not readily avail-able. Nesting may occur in the groundor in any sheltered location. Nests areconstructed of shredded fibrous mate-rials such as paper, burlap, or othersimilar items, and generally have theappearance of a “ball” of material

loosely woven together. They are usu-ally 4 to 6 inches (10.2 to 15.2 cm) indiameter.

Litters of 5 or 6 young are born 19 to21 days after mating, although femalesthat conceive while still nursing mayhave a slightly longer gestation period.Mice are born hairless and with theireyes closed. They grow rapidly, andafter 2 weeks they are covered withhair and their eyes and ears are open.They begin to make short excursionsfrom the nest and eat solid food at 3weeks. Weaning soon follows, andmice are sexually mature at 6 to 10weeks of age.

Mice may breed year-round, but whenliving outdoors, they breed mostly inspring and fall. A female may have 5to 10 litters per year. Mouse popula-tions can therefore grow rapidly undergood conditions, although breedingand survival of young decline mark-edly when population densitiesbecome high.

House mice have physical capabilitiesthat enable them to gain entry to struc-tures by gnawing, climbing, jumping,and swimming. For more detailedinformation on their physical abilitiesand the resulting need to designrodent-proof structures, see the chap-ter Rodent-Proof Construction andExclusion Methods.

Studies indicate that during its dailyactivities, a mouse normally travels anarea averaging 10 to 30 feet (3 m to9 m) in diameter. Mice seldom travelfarther than this to obtain food orwater. Because of their limited move-ment and feeding behavior, both ofwhich differ from those of commensalrats, they are much more difficult tocontrol in some situations.

Mice constantly explore and learnabout their environment, memorizingthe locations of pathways, obstacles,food and water, shelter, and other ele-ments in their domain. They quicklydetect new objects in their environ-ment but, unlike rats, do not fear them.Thus, they will almost immediatelyenter bait stations and sample newfoods (baits). The degree to whichmice consume a particular food

b

a

Fig. 2. Tracks left in dust by (a) Norway rat and (b) house mouse.

depends on the flavor of the food inaddition to its physiological effect.Mice may reject baits simply becausethey do not taste as good as otheravailable foods.

If the bait contains poison or someother substance that produces an illeffect (but not death) within a fewhours, the bait will often become asso-ciated with the illness. Bait shyness canpersist for weeks or months and maybe transferred to nontoxic foods ofsimilar types. Prebaiting, that is, train-ing mice to feed repeatedly on non-toxic bait for a period of days prior toapplying the toxicant in the bait, willlargely prevent sublethal doses andthus bait shyness. It will also reducethe number of mice left to be bait shy.Prebaiting is especially recommendedwith zinc phosphide baits. All of theother toxic baits currently registeredfor house mice are chronic or slow-acting. Because of this slow action, themice’s subsequent illness is not associ-ated with the bait even if a sublethaldose is consumed; thus, bait shynessdoes not usually occur. These baits, ineffect, serve as their own prebait.

Damage and DamageIdentification

When house mice live in or aroundstructures, they almost always causesome degree of economic damage. Inhomes and commercial buildings, theymay feed on various stored food itemsor pet foods. In addition, they usuallycontaminate foodstuffs with theirurine, droppings, and hair. On farms,they may cause damage to feed stor-age structures and feed transportingequipment. A single mouse eats onlyabout 3 grams of food per day (8pounds [3.6 kg] per year) but destroysconsiderably more food than it con-sumes because of its habit of nibblingon many foods and discarding par-tially eaten items.

House mice living in fields may dig upand feed on newly planted grain, ormay cause some damage to cropsbefore harvest. But losses in storedfoods are considerably greater. Micecommonly damage containers and

packaging materials in warehouseswhere food and feeds are stored.Much of this loss is due to contamina-tion with droppings and urine, makingfood unfit for human consumption.

House mice cause structural damageto buildings by their gnawing andnest-building activities. In livestockconfinement facilities and similarstructures, they may quickly causeextensive damage to insulation insidewalls and attics. Such damage alsooccurs in homes, apartments, offices,and commercial buildings but usuallyat a slower rate because mouse popu-lations in such structures are smaller.House mice often make homes in largeelectrical appliances, and here theymay chew up wiring as well as insula-tion, resulting in short circuits whichcreate fire hazards or other malfunc-tions that are expensive to repair. Micemay also damage stored items inattics, basements, garages, or muse-ums. Damaged family heirlooms,paintings, books, documents, andother such items may be impossible toreplace.

Among the diseases mice or their para-sites may transmit to humans aresalmonellosis (food poisoning), rickett-sialpox, and lymphocytic choriomen-ingitis. Mice may also carry lepto-spirosis, ratbite fever, tapeworms, andorganisms that can cause ringworm (a

fungal skin disease) in humans. Theyhave also been found to act as reser-voirs or transmitters of diseases of vet-erinary importance, such as swine dys-entery, a serious bacterial disease ofswine often called “bloody scours.”

Mouse Sign

The presence of house mice can bedetermined by a number of signsdescribed below:

Droppings may be found along run-ways, in feeding areas, and near shel-ter. Differentiating between mousedroppings and those of certain insectsmay be difficult. Mouse droppings areabout 1/4 inch (0.6 cm) long, whereasthose of cockroaches are usually 1/8 to1/4 inch (0.3 to 0.6 cm) long and undera magnifying glass show distinct longi-tudinal ridges and squared-off ends. Incomparison, droppings of bats containinsect fragments and are more easilycrushed between the fingers.

Tracks, including footprints or tailmarks, may be seen on dusty surfacesor in mud (Fig. 2). A tracking patchmade of flour, rolled smooth with acylindrical object, can be placed inpathways overnight to determine ifrodents are present.

Urine, both wet and dry, will fluo-resce under ultraviolet light, althoughso will some other materials. Urine

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Fig. 3. Rub marks along beams, rafters, or other travel routes give evidence of rodent activity. Mouserub marks can be distinguished from those of rats by their smaller size.

stains may occur along travelways orin feeding areas.

Smudge marks (rub marks) mayoccur on beams, rafters, pipes, walls,and other parts of structures. They arethe result of oil and dirt rubbing offmice’s fur along frequently traveledroutes (Fig. 3). They may be less appar-ent than rub marks left by rats.

Gnawing may be visible on doors,ledges, in corners, in wall material, onstored materials, or on other surfaceswherever mice are present. Fresh accu-mulations of wood shavings, insula-tion, and other gnawed materialindicate active infestations. Size ofentry holes (often 1 1/2 inches [3.8 cm]in diameter or less for mice, 2 inches [5cm] or larger for rat) or tooth markscan be used to distinguish rat gnawingfrom mouse gnawing. Mice keep theirpaired incisor teeth, which grow con-tinuously, worn down by gnawing onhard surfaces and by working themagainst each other.

Sounds such as gnawing, climbing inwalls, running across the upper sur-face of ceilings, and squeaks are com-mon where mice are present.

Visual sightings of mice may bepossible during daylight hours, andmice also can be seen after dark withthe aid of a flashlight or spotlight.

Nests frequently are found whencleaning garages, closets, attics, base-ments, and outbuildings where miceare present. They consist of fine, shred-ded fibrous materials.

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Odors may indicate the presence ofhouse mice. A characteristic muskyodor is a positive indication that housemice are present, and this odor can beused to differentiate their presencefrom that of rats.

Estimating Mouse Numbers

Mouse sign and visual sightings are oflimited value in accurately estimatingmouse numbers, but they are the sim-plest and often the only practicalmethod available. Search premisesthoroughly when looking for mice. Instructures, searches should includeattics, basements, around foundations,crawl spaces, and behind and understored materials.

One method to detect the presence ofmice is to make nontoxic tracking-dustpatches of flour or talc at 20- to 30-foot(6- to 9-m) intervals throughout astructure. The number of patchesshowing tracks after 24 hours, and theabundance of tracks in each patch,indicate the size of the population.Because house mice, unlike rats, donot travel far from their nests or shel-ter, the percentage of patches showingtracks is a good indicator of the rela-tive size and distribution of the mousepopulation.

Snap trapping is also an excellent wayto determine the presence of mice. Arelative index of mouse abundance canbe calculated from the number of micetrapped for a certain number of trapsset during 1 or more nights (for ex-ample, 35 mice caught per 100 trapnights).

Legal Status

House mice are not protected by law.They may be controlled using any pes-ticide registered by federal or state au-thorities for this purpose, or they maybe controlled by use of mechanicalmethods such as traps.

Damage Prevention andControl Methods

Effective prevention and control ofhouse mouse damage involves threeaspects: rodent-proof construction,sanitation, and population reductionby means of traps, toxicants, or fumi-gants. The first two are useful as pre-ventive measures, but when a housemouse infestation already exists, someform of population reduction is almostalways necessary. A flow chart outlin-ing steps in controlling house mice isfound in figure 4.

Control of house mice differs in impor-tant ways from the control of Norwayor roof rats. Mice are smaller andtherefore can enter narrower openings,making rodent-proofing more difficult.They have limited areas of movement(home range) and require little or nofree water. While having a reproduc-tive capability that is higher than thatof rats, house mice are usually less sen-sitive (often far less sensitive) to manyrodenticides. Persons who do not takethese differences into account whenattempting house mouse control mayexpect poor results.

After rats are controlled at a givenlocation, house mice may increase innumbers by moving in from elsewhereor by reproduction. This may beexpected because habitats suitable forrats are usually even more suitable formice. One should anticipate that fol-lowing rat control, the potential forhouse mouse problems may increase,and control measures should be takenbefore mouse numbers reach highlevels.

YESNO

YES NO

YESNO

NO YES

NO YES

NO

Usetraps

Snaptraps

Mucaptrap

After using an anti-coagulant, do somemice remain?

Useanticoagulantrodenticide

Can an anticoagulantrodenticide be used

safely?

After using a single-dose toxicant, do somemice remain?

Use single-dose toxicant(assistance ofa pest controloperator maybe required).

Can a single-dosetoxicant be usedsafely?

Contact apest controloperator forfumigation.

Are the mice within abuilding or structure thatcan safely be fumigated?

Will the presence of deadmice cause an odor orsanitation problem?

Are mice numerous?NO

YES

Is a quick reduction inmouse numbers

needed?

Reduce orlimitshelter.

YES NO

Can mice’s shelter beremoved or limited?

Remove orlimit food

source

YES NO

Can mice’s food sourcebe removed or limited?

Fig. 4. A flow chart of steps in controlling house mouse populations. Additional factors, such as the coscontrol methods, must be taken into account when planning a control program (see text).

YES

NO

YES

Exclusion

Physical barriers can prevent micefrom gaining entry to structures wherefood and shelter are available. Rodent-proofing is an important and oftenneglected aspect of rodent control. It isa relatively permanent form of controlthat can prevent damage from occur-ring.

To exclude mice, seal all holes andopenings larger than 1/4 inch (0.6 cm)across. Rodent-proofing should bedone with heavy materials that willresist rodent gnawing. These includeconcrete mortar, galvanized sheetmetal, and heavy-gauge hardwarecloth. For more detailed informationon techniques of mouse-proof con-struction, see the chapter Rodent-Proof Construction and ExclusionMethods.

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ltiple-tures

t of particular

Glue boards(if not apt toentrapchildren, pets,or wildlife)

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12" white band

Fig. 5. A 12-inch (30.5-cm) white painted band makes inspection for rodent sign easier and reminds personnel not to store commodities too close to walls.

Habitat Modification

Sanitation, which includes goodhousekeeping practices and properstorage and handling of food materi-als, feed, and garbage, is often stressedas a method of rodent control. Unfor-tunately, even the best sanitation willnot eliminate house mice. It will, how-ever, aid in control by permittingeasier detection of mouse sign, increas-ing effectiveness of traps and baits byreducing competing food items, andby preventing mice from flourishingand reaching high populations.

Although house mice are less depen-dent upon humans for their existencethan are Norway rats, they are muchmore adaptable to living with people.They require very little space and onlysmall amounts of food. Mice have beenknown to inhabit buildings evenbefore construction has been complete,living off the crumbs and scraps ofworker’s lunches. In offices, mice maylive behind cabinets or furniture andfeed on scraps or crumbs from lunchesand snacks and on cookies or candybars kept in desks. In homes, they mayfind ample food in kitchens, and in thegarage they will eat sacked or spilledpet food, grass seed, or insects such ascockroaches. Thus, no matter howgood the sanitation, most buildings inwhich food is stored, prepared, or

6

consumed will support at least a fewmice. For this reason, a constant watchmust be kept for mice that may invadethe premises.

Where possible, store bulk foods inrodent-proof containers or rooms.Stack sacked or boxed foods in orderlyrows on pallets in a way that allowsfor thorough inspection for evidence ofmice. In such storage areas, keepstored materials away from walls. A12-inch (30.5-cm) white band paintedon the floor next to the wall serves as areminder to keep items away fromwalls. It also will allow you to detectrodent droppings or other sign moreeasily (Fig. 5). Sweep floors frequentlyto permit ready detection of freshdroppings.

When storing foods or feed on pallets,keep in mind that mice can jump upmore than 12 inches (30.5 cm) from aflat surface. They are also good climb-ers and can walk up surfaces such aswood or concrete (unless the surfaceshave a slick finish). Mice can live forconsiderable periods of time within apallet of feed without coming down tothe floor.

Regular removal of debris and controlof weeds from around structures willreduce the amount of shelter availableto rodents. In some instances, a strip of

heavy gravel placed adjacent to build-ing foundations or other structureswill reduce rodent burrowing at theselocations. In any event, keep theperimeter of buildings and other struc-tures clean of weeds and debris(including stacked lumber, firewood,and other stored materials) to discour-age rodent activity and to allow easierdetection of rodent sign.

Frightening

Mice are somewhat wary animals andcan be frightened by unfamiliarsounds or sounds coming from newlocations. Most rodents, however, canquickly become accustomed to newsounds heard repeatedly.

For years, devices that produce ultra-sonic sound that is claimed to controlrodents have come and gone on themarket. There is little evidence to sug-gest that rodents’ responses to nonspe-cific, high-frequency sound is anydifferent from their response to soundwithin the range of human hearing.

What is known about rodents andsound?

—Unusually loud, novel, or ultrasonicsounds, which rodents can hear, willfrighten them and may cause tempo-rary avoidance lasting from a few min-utes to a few weeks.

What is known about ultrasonicsound?

—It is very directional and does nottravel around corners well; thus,sound shadows or voids are created.

—Ultrasound does not travel very far.It loses its intensity rapidly as it leavesthe source.

—Ultrasound has not been shown todrive established rodents out of build-ings or areas, nor has it been proven tocause above-normal mortality in theirpopulations. While it is possible tocause convulsions or permanent physi-ological damage to rodents with ultra-sound, the intensity of such soundsmust be so great that damage tohumans or domestic animals wouldalso be likely. Commercial ultrasonicpest control devices do not producesound of such intensity.

Recent tests of commercial ultrasonicdevices have indicated that rodentsmay be repelled from the immediatearea of the ultrasound for a few days,but then will return and resume nor-mal activities. Other tests have shownthe degree of repellency to dependupon the particular ultrasonic frequen-cies used, their intensity, and the pre-existing condition of the rodentinfestation. Ultrasonic sound has verylimited usefulness in rodent control.The advertising claims for many

Table 1. Anticoagulants used for house

Common name andtypical trade names Chemical name

Hydroxycoumarins

Warfarin (Final®and others) 3-(α-acetonylbenzy

Brodifacoum 3-[3(4'-bromo[1,1’b(Talon®)* 1-naphthalenyl]-4-h

Bromadiolone (Maki®, 3-[3-(4'-bromo[1,1’bContrac®)* phenylpropyl]-4-hy

Difethialone* [(bromo-4'-[biphen3-hydroxy-4, 2H-1-

Indandiones

Chlorophacinone(RoZol®) 2-[(p-chlorophenyl)

Diphacinone (Ditrac®) 2-diphenylacetyl-1

Pindone (Pival®, Pivalyn®) 2-pivalyl-1,3-indan

* Second-generation anticoagulants especially usef

commercial devices are unsubstan-tiated by scientific research. Since com-mercial ultrasonic devices are oftenexpensive and of questionable effec-tiveness, they cannot be recommendedas a solution to rodent problems.

Repellents

Rodents find some types of tastes andodors objectionable, but chemicalrepellents are seldom a practical solu-tion to mouse infestations. Substancessuch as moth balls (naphthalene) orhousehold ammonia, in sufficient con-centration, may have at least tempo-rary effects in keeping mice out ofcertain enclosed areas. These are notspecifically registered by the EPA asmouse repellents, however.

Ro-pel® is registered for use in repel-ling house mice and other rodentsfrom gnawing on trees, poles, fences,shrubs, garbage, and other objects.Little information is currently availableon its effectiveness against house mice.

Other solutions to rodent problems,including rodent-proof constructionand methods of population reduction,are usually more permanent and cost-effective than the use of repellents.

Toxicants

Rodenticides were formerly classifiedinto two groups, single-dose (acute)

mouse control in the United States.Usu

Foodbai

l)-4-hydroxycoumarin X

iphenyl]-4-yl)-1,2,3,4-tetrahydro-ydroxy-2H-1-benzopyran-2-one X

iphenyl]-4-yl)-3-hydroxy-1-droxy-2H-1-benzopyran-2-one X

yl-1-1']-yl-4) 3-tetrahydro-1,2,3,4-napthyl-1] Xbenzo-thiopyran-2-one

phenylacetyl]-1,3-indandione X

,3-indandione X

dione X

ul for the control of warfarin-resistant rats and mice

toxicants and multiple-dose (chronic)toxicants. However, the complexity inmode of action of newer rodenticidesmakes these classifications outdated. Aclassification into two groups, the firstgroup including all anticoagulants andthe second group all other compounds(“non-anticoagulants”), is currentlymore useful.

Anticoagulants (slow-acting,chronic toxicants). House mice aresusceptible to all of the various anti-coagulant rodenticides (Table 1), butthey are generally less sensitive (oftenfar less sensitive) to the active ingre-dients than are Norway or roof rats. Itusually requires a few more feedingsto produce death with the first-genera-tion anticoagulants (such as warfarin,diphacinone, and chlorophacinone)than with the second-generation anti-coagulants (such as brodifacoum andbromadiolone). All anticoagulants pro-vide good to excellent house mousecontrol when prepared in acceptablebaits. A new second-generation anti-coagulant, difethialone, is presentlybeing developed and EPA registrationis anticipated in the near future. Thecharacteristics of the various antico-agulant rodenticides are describedfurther under Anticoagulants in thePesticides section, and in the chapterNorway Rats.

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al types of formulations PercentTracking active ingredient

t Liquid powder used in food bait

X 0.025

0.005

0.005

0.0025

X 0.005

X 0.005

X 0.025

.

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Because of their similarity in mode ofaction, all anticoagulant baits are usedin a similar fashion. Label directionscommonly instruct the user to “main-tain a continuous supply of bait for 15days or until feeding ceases,” thusensuring that the entire mouse popula-tion has ample opportunity to ingest alethal dose of the bait. Anticoagulantshave the same effect on nearly allwarm-blooded animals, but the sensi-tivity to these toxicants varies amongspecies. If misused, anticoagulantrodenticides can be lethal to nontargetanimals such as dogs, pigs, and cats.Additionally, residues of anticoagu-lants which are present in the bodies ofdead or dying rodents can cause toxiceffects to scavengers and predators. Ingeneral, however, the secondary poi-soning hazard from anticoagulants isrelatively low.

Brodifacoum and bromadiolone baits,because of their potential to be lethal ina single feeding, can be more effectivethan the other anticoagulants in certainsituations. Chlorophacinone (RoZol®)and diphacinone (Ditrac®) are similarto each other in potency and are moretoxic than the anticoagulant com-pounds developed earlier. Thus, theyare formulated at lower concentra-tions. Chlorophacinone and diphaci-none may kill some mice in a singlefeeding, but multiple feedings areneeded to give adequate control of amouse population.

Pindone (Pival®, Pivalyn®) is also lesspotent than chlorophacinone ordiphacinone, and is similar to warfarinin effectiveness against house mice. Ithas some properties that resist insectsand growth of mold in prepared baits.

Warfarin (Final® and other tradenames) was the first marketed anti-coagulant and is, therefore, the bestknown and most widely used. It iseffective against house mice, althoughsome warfarin contains small quanti-ties of contaminants that apparentlycan reduce bait acceptance. This hasbeen resolved with the development ofencapsulated warfarin.

Anticoagulant Resistance. Withinany population of house mice, some

8

individuals are less sensitive toanticoagulants than others. Whereanticoagulants have been used overlong periods of time at a particularlocation, there is an increased potentialfor the existence of a population that issomewhat resistant to the lethal effectsof the baits. Such resistant populationsof house mice have been identified at anumber of locations throughout theUnited States. Although not common,resistance may be underestimatedbecause relatively few resistancestudies have been conducted on housemice. Nevertheless, resistance is of lit-tle consequence in the control of housemice with the newer rodenticidesavailable. When anticoagulant resis-tance to the first-generation anticoagu-lants is known or suspected, use ofthese compounds should be avoidedin favor of the second-generationanticoagulants or one of the non-anticoagulant products.

Anticoagulant Bait Failure.Resistance is only one (and perhapsthe least likely) reason for failure in thecontrol of mice with anticoagulantbaits. Control with baits that are highlyaccepted may fail for one or more ofthe following reasons:

— Too short a period of bait exposure.

— Insufficient bait and insufficientreplenishment of bait (none remainsfrom one baiting to the next).

— Too few bait stations and/or too farapart. For mice, stations should bewithin 6 feet (2 m) of one another inareas where mice are active.

— Too small a control area, permittingmice to move in from untreatedadjacent areas.

— Genetic resistance to the anticoagu-lant. Although this is unlikely, itshould be suspected if about thesame amount of bait is taken dailyfor several weeks.

Reasons for failure to achieve controlwith anticoagulant baits that arepoorly accepted:

— Poor bait choice, or bait formulatedimproperly. Other foods are moreattractive to the mice.

— Improperly placed bait stations.Other foods are more convenient tothe mice.

— Abundance of other food choices.

— Tainted bait: the bait has becomemoldy, rancid, insect-infested, orcontaminated with other materialthat reduces acceptance. Discardold bait periodically, and replace itwith fresh.

Occasionally, mice accept bait well andan initial population reduction is suc-cessful. Then bait acceptance appearsto stop although some mice remain. Insuch instances, it is likely that the re-maining mice never accepted the bait,either because of its formulation orplacement. The best strategy is toswitch to a different bait formulation,place baits at different locations, and/or use other control methods such astraps.

Other Rodenticides. The olderrodenticides, formerly referred to asacute toxicants, such as arsenic triox-ide, phosphorus, strychnine, and Com-pound 1080, are no longer registeredfor house mice. Newer rodenticidesare much more effective and haveresulted in the phasing out of theseolder materials over the last 20 years.

At present, three non-anticoagulantrodenticides (Table 2) are registered byEPA against house mice: bromethalin,cholecalciferol (vitamin D3), and zincphosphide. All are potentially usefulfor controlling anticoagulant-resistantpopulations of house mice.

Of these active ingredients, brometha-lin and cholecalciferol are formulatedto serve as chronic rodenticides,applied so that house mice will havethe opportunity to feed on the baitsone or more times over the period ofone to several days. Bait acceptance isgenerally good when formulationsappropriate for house mice are select-ed. Zinc phosphide differs from theother two compounds in that prebait-ing (offering mice similar but nontoxicbait prior to applying the zinc phos-phide-treated bait) is recommended toincrease bait acceptance. Zinc phos-phide baits are not designed to be left

Table 2. Other (non-anticoagulant) rodenticides used to control house mice in the United States.Acute oral PercentLD50 for Time activemice, to ingredient Relative

Common Name Chemical Name mg/kg death Odor Taste in food bait hazard Mode of Action

Bromethalin N-methyl-2,4-dinitro-N- 5.25-8.13 2-4 days None Slight 0.01 Moderate Central nervous(Assault®, (2,4,6-tribromophenyl)- system depressionVengeance®) 6-(trifluoromethyl) and paralysis

benzenamine

Cholecalciferol 9,10-Seocholesta-5,7,10 42.5 3-4 days Slight None 0.075 Low to Mobilizes calcium(vitamin D3, (19)-trein-3 betaol moderate resulting in deathQuintox®) from hypercalcemia

Zinc phosphide Zinc phosphide 40 1/2-20 hours Strong Strong 1.0-2.0 Moderate Phosphine gas enterscirculatory system;heart paralysis,gastrointestinal andliver damage

available to mice for more than a fewdays, as continued exposure is likely toresult in bait shyness within thepopulation. Be sure to follow label rec-ommendations on any specific productto achieve best success.

Bait Selection and Formulation

Oatmeal, ground or rolled wheat,rolled barley, ground or rolled milo,and corn have been successfully usedas chief ingredients of toxic baits forhouse mice. Grass seed, such as wholecanary grass seed (Phalaris canarienses),is often highly accepted by house miceand can be very effective as a principalbait ingredient. In general, the fresherthe bait, the better it will be acceptedby mice. Rodent baits should alwaysbe made from high-quality food mate-rials, and baits should be replaced orreplenished regularly.

Food preferences may vary amongmouse populations and individuals.Bait materials similar to foods mice are

Fig. 6. Various types of place packs containingrodenticides are commercially available.

accustomed to eating are often a goodchoice, particularly if their normalfoods are limited or can be made lessavailable to them. In past years, manypeople involved in house mouse con-trol preferred to mix their own baits soas to tailor them to the food preferenceof a specific mouse population. Today,there is a wide selection of ready-to-use baits which are commerciallyavailable. It is still important, particu-larly in moderate- to large-scale mousecontrol programs, to check for differ-ences in bait acceptance among candi-date baits prior to investing time andmoney in a specific bait product. Placeabout 1/2 ounce (14 g) of each of sev-eral ready-to-use baits about 4 inches(10 cm) apart in several locationswhere mice are present. Check baitsthe next day to see which ones arepreferred.

Ready-to-use baits come in a variety offormulations. Grain-based baits in aloose meal or pelleted form are

Fig. 7. Wax and extruded bait blocks are useful in dquickly.

available in bulk or packaged in smallplastic, cellophane, or paper “placepacks” (Fig. 6). These packets keep baitfresh and make it easy to place baitsinto burrows, walls, or other locations.Mice will gnaw into these bags to feedon an acceptable bait. Pelleted baitscan more easily be carried by mice toother locations. Such hoarding of foodby mice is not uncommon. It mayresult in amounts of bait being movedto places where it is undetected or dif-ficult to recover and may, if accessible,be hazardous to nontarget species. Onthe other hand, pelleted bait avoidssome problems common to loose baits— settling out of different-sized par-ticles during shipment and unevenmixing of the toxicant. Pellets are eas-ily manipulated by mice, increasingthe attractiveness of this form of bait.

Anticoagulant baits have also been for-mulated into wax and extruded blocks(Fig. 7). These are particularly usefulwhere moisture may cause loose grain

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amp locations where loose baits become spoiled

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baits to spoil. Mice accept paraffinblock baits less readily than loose orpelleted grain baits, but acceptance ofextruded bait blocks is high.

Where no water is available, water orfood items of high moisture contentare often more readily accepted thandry baits. Sodium salts of anticoagu-lants are available as concentrates to bemixed with water, making a liquid bait(Fig. 8). Although mice require little orno water to survive, they will readilydrink it when available. Water baitscan be an effective supplement to othercontrol measures where water isscarce. They are particularly useful ingrain storage structures, warehouses,and other such locations. Rodents aremore easily able to detect anticoagu-lants in water baits than in food baits;therefore, up to 5% sugar is sometimesadded to liquid baits to increaserodents’ acceptance of the bait solu-tion. Since water is attractive to mostanimals, use water baits in ways thatprevent nontarget animals from drink-ing them.

Bait Stations

Bait stations (bait boxes) may increaseboth the effectiveness and safety ofrodenticides. They came into generaluse after the development of the first-generation anticoagulants, whichrequire that a continuous supply ofbait be made available to rodents. Baitstations are useful because they:

— protect bait from moisture anddust;

0

Fig. 8. Liquid baits can be placed in fonts orother similar containers.

— provide a protected place forrodents to feed, allowing them tofeel more secure. This is an impor-tant advantage when baiting mice,which apparently like to spend timefeeding inside such bait boxes;

— keep other animals (pets, livestock,desirable wildlife) and childrenaway from hazardous bait;

— allow placement of bait in locationswhere it would otherwise be diffi-cult because of weather or potentialhazards to nontarget animals;

— help prevent the accidental spillingof bait;

— allow easy inspection of bait to seeif rodents are feeding on it.

Fig. 9. Examples of commercially manufactured ro

Kinds of Bait Stations. Bait sta-tions can contain solid baits (foodbaits), liquid baits, or both. Bait boxescan be purchased from commercialsuppliers or made at home. Manufac-tured bait boxes made of plastic, card-board, or metal are sold to pest controlcompanies and to the public (Fig. 9) insizes for rats or mice. Some farm sup-ply and agricultural chemical supplystores have them in stock or can orderthem. Recent research suggests micemay prefer to feed in cardboard baitstations rather than plastic ones.

Bait boxes can be built from scrap ma-terials, and homemade stations can bedesigned to fit individual needs. Makethem out of sturdy materials so theycannot be easily knocked out of place

dent bait stations.

18"

2 1/2"

Fig. 12. A homwell as solid b

Fig. 10. A flat board nailed to a wall protects rodent bait from nontarget animals and allows rodentsto feed in a sheltered location. The board should be at least 18 inches (45.7 cm) long to keep pets andchildren from reaching the bait.

18"

Fig. 11. Rodent bait station made from a length of pipe. Pipediameter can be 2 to 3 inches (5.1 to 7.6 cm) for mice; 3 1/2 to6 inches (8.9 to 15.2 cm) for rats.

or damaged. Where children, pets, orlivestock are present, be careful toconstruct the stations so that the bait isaccessible only to rodents. Locks, seals,or concealed latches are often used tomake bait boxes more tamperproof.Clearly label all bait boxes or stationswith “Poison” or “Rodent Bait — DoNot Touch,” or with a similar warning.Some rodenticides or situations mayrequire use of tamper-resistance baitstations. If so, use only bait boxes orstations which are so designated, andalso be sure to secure them to build-ings by nailing or gluing them to wallsor floors in a way that will not permita person or animal to knock them overor shake the bait out.

Bait Station Design. Bait stationsshould be large enough to allow sev-eral rodents to feed at once. They canbe as simple as a flat board nailed at anangle to the bottom of a wall (Fig. 10),or a length of pipe into which bait canbe placed (Fig. 11). More elaborate sta-tions are completely enclosed and cancontain liquid as well as solid rodentbaits (Fig. 12). A hinged lid with achild-proof latch can be used for con-venience in inspecting permanentstations.

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emade rodent bait station can contain liquid asaits.

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Fig. 13. Rodent bait box attached to the top of open dividing wall in a swine confinement facility.When used in such locations, bait boxes must be securely fastened and out of pigs’ reach.

Bait stations for mice should have atleast two openings approximately 1inch (2.5 cm) in diameter. Locate thetwo holes on opposite sides of the sta-tion so that mice can see an alternateescape route as they enter the station.

Bait Station Maintenance. Baitsmust be fresh and of high quality.Mice may reject spoiled or stale foods.Provide enough fresh bait to allowrodents to eat all they want. Whenusing rodenticides designed for con-tinuous bait application (such as anti-coagulants), bait station maintenance isessential to a successful baiting effort.When bait boxes are first put out,check them daily and add fresh bait asneeded. After a short time, as rodentnumbers and feeding decline, checkthe boxes once every 2 to 4 weeks. Ifthe bait becomes moldy, musty, soiled,or insect-infested, empty the box andclean it, and then refill it with freshbait. Dispose of spoiled or uneaten baitin accordance with the label. Follow alllabel directions for the product you areusing.

Placement of Bait Stations. Housemice are active in a small area and lacknotable food preferences. Therefore,proper placement of baits or bait sta-tions is often more important than thetype of bait used. Mice will not visitbait stations, regardless of their con-tents, if not conveniently located inareas where they are active.

Where possible, place bait between therodents’ source of shelter and theirfood supply. Put bait boxes nearrodent burrows, against walls or alongtravel routes. Where mice are living insacked or boxed feed on pallets, baitsor traps may have to be placed on topof stacks or wedged in gaps within thestacks. In such situations, this “threedimensional” bait placement is impor-tant to obtain good control. Cautionshould be used in selecting controlmethods in such situations. Do not usebaits that will contaminate foodstuffs.For safety, it may not be wise to usetoxic baits in the vicinity of certainfoodstuffs. Traps or glue boards maybe used instead.

On farmsteads, bait station placementdepends on building design and use.

2

For example, in swine confinementbuildings it may be possible to attachbait boxes to wall ledges or the top ofpen dividing walls. Bait boxes may beplaced in attics or along floors or alleyswhere rodents are active (Fig. 13).Rodent tracks visible on dusty surfacesand their droppings often give clues towhere they are active.

Never place bait stations where live-stock, pets, or other animals can knockthem over. Spilled bait may be apotential hazard, particularly tosmaller animals.

Where buildings are not rodent-proof,permanent bait stations can be placedinside buildings, along the outside ofbuilding foundations, or around theperimeter. Bait stations will help keeprodent numbers at a low level whenmaintained regularly with fresh anti-coagulant bait. Rodents moving infrom nearby areas will be controlledbefore they can reproduce and causeserious damage.

Tracking Powders. Toxic dusts orpowders have been successfully usedfor many years to control mice andrats. When mice walk over a patch of

toxic powder, they pick some of it upon their feet and fur and later ingest itwhile grooming. Tracking powders areuseful in controlling mice where foodis plentiful and good bait acceptance isdifficult to achieve. Mice are morelikely to ingest a lethal amount of apoorly accepted toxicant applied bythis method than if it is mixed into abait material. There is little likelihoodof toxicant shyness developing whenusing tracking powders.

Because the amount of material amouse may ingest while grooming issmall, the concentration of activeingredient in tracking powders is con-siderably higher than in food baits thatutilize the same toxicant. Therefore,these materials can be more hazardousthan food baits. For the most part,tracking powders are used by profes-sional pest control operators andothers trained in rodent control. Track-ing powders containing either zincphosphide or anticoagulants are com-mercially available, although some areRestricted Use Pesticides.

Place tracking powders along run-ways, in walls, behind boards along

The double set increases your success. Double set placed parallel to the wall withtriggers to the outside.

Single trap set with trigger next to wall.

Wrong—trap too far from wall.Wrong—parallel set with triggers on the inside.Wrong—trigger not next to wall.

Fig. 14. Placement of snap traps.

walls, or on the floor of bait stations.Placement can be aided by using vari-ous types of sifters, shakers, or blow-ers. Dampness may cause the powderto cake and lessen its effectiveness.Care must be taken to place trackingpowders only where they cannot con-taminate food or animal feed, or wherenontarget animals cannot come intocontact with them. Do not place track-ing powders where mice can track thematerial onto food intended for use byhumans or domestic animals. Trackingpowders are not generally recom-mended for use in and around homesbecause of the potential hazards tochildren and pets. Where possible,remove tracking powder after therodent control program is completed.Tracking powders used in conjunctionwith baiting can provide very effectivemouse control.

Fumigants

Fumigants (toxic gases) are most com-monly used to control mice in struc-tures or containers such as feed bins,railway cars, or other enclosed areas.Aluminum phosphide, chloropicrin,and methyl bromide are currently reg-istered for this purpose. Some fumi-gant materials are registered for use inrodent burrows; however, housemouse burrows cannot be fumigated

efficiently or economically becausethey are small and often difficult tofind. Generally, control of house miceby fumigation is only practical andcost-effective in a very limited numberof situations. Fumigants are hazardousmaterials and should be applied onlyby persons well trained in their useand who possess the necessary safetyequipment.

Trapping

Trapping can be an effective method ofcontrolling mice, but it requires morelabor than most other methods. Trap-ping is recommended where poisonsseem inadvisable. It is the preferredmethod to try first in homes, garages,and other small structures where theremay be only a few mice present.

Trapping has several advantages: (1) itdoes not rely on inherently hazardousrodenticides; (2) it permits the user toview his or her success; and (3) itallows for disposal of the mice, therebyeliminating odor problems fromdecomposing carcasses that mayremain when poisoning is done withinbuildings.

The simple, inexpensive, wood-basedsnap trap is available in most hard-ware and farm supply stores. Trapsshould be baited with a small piece of

nutmeat, chocolate candy, dried fruit,or bacon tied securely to the trigger.Peanut butter or marshmallows alsomay be used as bait. Because mice arealways in search of nesting materials, asmall cotton ball will also work as abait when attached securely to the trig-ger. Food baits that become stale losetheir effectiveness.

Set traps close to walls, behind objects,in dark places, and in locations wheremouse activity is seen. Place the trapsso that when mice follow their naturalcourse of travel (usually close to awall) they will pass directly over thetrigger (Fig. 14). Set traps so that thetrigger is sensitive and will spring eas-ily. Effectiveness can be increased byenlarging the trigger. Attach a squareof cardboard, metal, or screen wirethat fits just inside the wire deadfall(Fig. 15).

Use enough traps to make the cam-paign short and decisive. Mice seldomventure far from their shelter and foodsupply, so traps should be spaced nomore than about 6 feet (1.8 m) apart inareas where mice are active. Althoughmice are not nearly as afraid of newobjects as rats are, leaving the trapsbaited but unset until the bait is takenat least once will reduce the chance ofmice escaping the trap and becomingtrap-shy.

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Expanded trigger

A box or board placed toadvantage may guide mouseinto trap.

Place traps acrossobvious runways,or where runs areconfined.

Fig. 15. Expanded-trigger traps, when properly placed, can be very effective.

Fig. 16. Automatic multiple-capture mouse traps are commercially available (for example: left, TinCat®; right, Ketch-All®).

Multiple-capture (automatic) mousetraps such as the Ketch-All® andVictor Tin Cat® (Fig. 16) are availablefrom some hardware and farm supplystores as well as from pest controlequipment distributors. These trapswork on the principle that mice entersmall holes without hesitation. TheKetch-All® has a wind-up spring thatpowers a rotating mechanism. Whentriggered, the mechanism entraps micein a holding compartment. The TinCat® has one-way doors that mice can-not exit. Such traps may catch manymice in a single setting, but should bechecked and emptied periodically sothat mice do not die of starvation orexposure in the traps.

Various types of box-type traps(Sherman-type and others) that cap-ture one mouse at a setting are usedprimarily for research purposes. Thedesire to “build a better mousetrap”keeps a variety of traps of variableeffectiveness coming and going on theretail market.

Keep traps reasonably clean and ingood working condition. They can becleaned with a hot detergent solutionand a stiff brush. Human and dead-mouse odors on traps are not knownto reduce trapping success.

An alternative to traps are glue boards,which catch and hold mice attemptingto cross them, much the way flypapercatches flies. Place glue boards wher-ever mice travel—along walls or inestablished runways. Do not use glueboards where children, pets, or desir-able wildlife can contact them. Glueboards lose their effectiveness in dustyareas unless covered, and temperatureextremes may affect the tackiness ofsome glues. They are considered lesseffective for capturing rats than formice. Glue boards can be purchasedready-to-use, or they can be made.

Euthanize live, trapped rodents by car-bon dioxide asphyxiation or use a stickto kill them with sharp blows to thebase of the skull. For further informa-tion on glue boards, see the sectionSupplies and Materials.

Other Methods

Some dogs and cats will catch and killmice and rats. There are few situa-tions, however, in which they will doso sufficiently to control rodent popu-lations. Around most structures, micecan find many places to hide and reartheir young out of the reach of suchpredators. Cats probably cannot elimi-nate existing mouse populations, butin some situations they may be able toprevent reinfestations once mice havebeen controlled. Farm cats, if sufficientin number and supplementally fed,may serve this function.

In urban and suburban areas, it is notuncommon to find rodents living inclose association with cats and dogs,relying on cat and dog food for nour-ishment. Mice frequently live beneathdog houses and soon learn they canfeed on their food when they areabsent or asleep.

Economics of Damageand Control

Accurate data on mouse damage,control, and their cost are difficult toobtain. Estimates of losses of food-stuffs, structural damage, and theamount of labor and materials expend-ed to control mice are usually onlyeducated guesses.

In one survey of corn in a midwesternstate, 76% of about 1,000 grain sampleswere contaminated with rodentdroppings. Mouse droppings outnum-bered rat droppings twelve to one. Ahouse mouse produces about 36,000droppings in a year’s time. Mouse in-festations are so widespread that drop-pings and hairs often end up in manytypes of food commodities intendedfor human use. Certain levels of rodentcontamination are grounds for con-demning food commodities.

Structural damage caused by rodentscan be expensive. In recent years, thetrend toward use of insulated confine-ment facilities to raise swine in thenorthern Great Plains has led to an

increased amount of rodent damage.Mice, in particular, are very destruc-tive to rigid foam, fiberglass batt, andother types of insulation in walls andattics of such facilities. In one smallswine finishing building near Lincoln,Nebraska, rodent damage required theproducer to spend $5,000 in repairs tothe facility only 3 years after initialconstruction.

Acknowledgments

I thank Rex E. Marsh for reviewing a previousversion of this chapter and providing manyhelpful comments. Portions of therecommendations on toxicant use are takendirectly from his chapter Roof Rats in thismanual. Other material contained in thischapter is derived from Brooks (1973), Marshand Howard (1981), and Pratt et al. (1977),among other sources.

Figure 1 is from Schwartz and Schwartz (1981).

Figures 2, 5, and 15 were adapted from Pratt etal. (1977) by Jill Sack Johnson.

Figures 3 and 14 were adapted from Howardand Marsh (1981) by Jill Sack Johnson.

Figure 4 from Hygnstrom and Virchow (1992).

Figures 6, 7, and 8 were developed by Jill SackJohnson.

Figures 9, 12, and 13 are by Frances I. Gould,University of Nebraska-Lincoln, CooperativeExtension.

Figures 10 and 11 were adapted from Pratt et al.(1977) by Frances I. Gould.

For AdditionalInformation

Berry, R. J. 1981. Town mouse, country mouse:adaptation and adaptability in Musdomesticus (M. musculus d). Mammal Rev.11:91-136.

Berry, R. J., ed. 1981. Biology of the housemouse. Symp. Zool. Soc. London, No. 47.715 pp.

Bohills, S. T., A. P. Meehan, and S. P. Leonard.1982. Advantages of bait boxes in housemouse control. International Pest Control24(2):34, 35, 37.

Bronson, F. H. 1979. The reproductive ecology ofthe house mouse. Quarterly Rev. Biol.54(3):265-299.

Brooks, J. E. 1973. A review of commensalrodents and their control. CRC Critical Rev.Environ. Control 3:405-453.

Burt, W. H., and R. P. Grossenheider. 1976. Afield guide to the mammals, 3rd ed.Houghton Mifflin Co., Boston. 289 pp.

Chitty, D., and H. N. Southern. 1954. Control ofrats and mice, vol. 1-3. Clarendon Press,Oxford.

Corrigan, R. M., C. A. Towell, and R. E.Williams. 1992. Development of rodentcontrol technology for confined swinefacilities. Proc. Vertebr. Pest Conf. 15:280-285.

Crowcroft, P., and J. N. R. Jeffers. 1961.Variability in the behavior of wild housemice (Mus musculus L.) towards live traps.Proc. Zool. Soc. London 137:573-582.

Davis, D. E. 1981. Environmental control ofrodents. Pages 493-498 in D. Pimentel, ed.CRC handbook of pest management inagriculture, vol. 1. CRC Press, Inc., BocaRaton, Florida.

Fitzwater, W. D. 1982. Bird limes and rat glues— sticky situations. Proc. Vertebr. Pest Conf.10:17-20.

Frantz, S. C., and D. E. Davis. 1991. Bionomicsand integrated pest management ofcommensal rodents. Pages 243-313 in J. R.Gorham, ed. Ecology and management offood-industry pests. Food Drug Admin.Tech. Bull. 4, Assoc. Official AnalyticalChem. Arlington, VA.

Haines, H., and K. Schmidt-Neilsen. 1967. Waterdeprivation in wild house mice. Physiol.Zool. 40:424-431.

Howard, W. E., and R. E. Marsh. 1981. The rat:its biology and control. Div. Agric. Sci. Univ.California, Leaflet 2896 (revised). 30 pp.

Humphries, R. E., A. P. Meehan, and R. M. Sibly.1992. The characteristics and history ofbehavioural resistance in inner-city housemice (Mus domesticus) in the U.K. Proc.Vertebr. Pest Conf. 15:161-164.

Hygnstrom, S. E., and D. R. Virchow. 1992.Controlling house mice. Univ. NebraskaCoop. Ext. NebGuide G92-1105-A. 4 pp.

Jackson, W. B. 1990. Rats and mice. Pages 9-85 inA. Mallis, ed. Handbook of pest control.Franzak and Foster Co., Cleveland, OH.

Kaukeinen, D. E. 1982. A review of thesecondary poisoning hazard potential towildlife from the use of anticoagulantrodenticides. Proc. Vertebr. Pest Conf.10:151-158.

Kaukeinen, D. E. 1984. Resistance: what weneed to know. Pest Manage. 3(3):26-30.

Knote, C. E. 1988. Stopping house mice buildinginfestations through exterior control. Proc.Vertebr. Pest Conf. 13:107-111.

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Labov, J. B. 1981. Male social status, physiology,and ability to block pregnancies in femalehouse mice (Mus musculus). Behav. Ecol.Sociobiol. 8:287-291.

Marsh, R. E., and W. E. Howard. 1981. Thehouse mouse: its biology and control. Div.Agric. Sci. Univ. California, Leaflet 2945(revised). 30 pp.

Meehan, A. P. 1984. Rats and mice: their biologyand control. Rentokil Ltd., E. Grinstead, U.K.383 pp.

Morris, K. D., and D. E. Kaukeinen. 1988.Comparative evaluation of tamper-proofmouse bait stations. Proc. Vertebr. Pest Conf.13:101-106.

Petras, M. L., and J. C. Topping. 1981. Studies ofnatural populations of Mus. VI. Sizes ofpopulations inhabiting corn cribs insouthwestern Ontario. J. Mammal. 62:146-153.

Pratt, H. D., B. F. Bjornson, and K. S. Littig. 1977.Control of domestic rats and mice. PublicHealth Serv., US Dep. Health, Educ. Welfare,Pub. No. (CDC) 77-841. 47 pp.

Robbins, R. J. 1980. Taste-aversion learning andits implications for rodent control. Proc.Vertebr. Pest Conf. 9:114-121.

Rowe, F. P. 1966. Economic importance of thehouse mouse (Mus musculus L.). WorldHealth Organiz., Vector Control, Pub. 66.217,paper 1.4:21-26.

Schwartz, C. W., and E. R. Schwartz. 1981.House mouse. Pages 248-252 in The wildmammals of Missouri, rev. ed. Univ.Missouri Press, Columbia. 356 pp.

Shenker, A. M. 1973. The house mouse inLondon. Mammal Rev. 3:64-69.

Weber, W. J. 1982. Diseases transmitted by ratsand mice. Thomson Pub. Fresno, California.182 pp.

EditorsScott E. HygnstromRobert M. TimmGary E. Larson