Voles (Meadow Mice)

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PEST NOTES Publication 7439University of California

Statewide Integrated Pest Management Program

Agriculture and Natural Resources

June 2010

Six species of voles from the genusMi-

crotus occur in California. Collectivelythey are called either meadow miceor voles. Two species are responsiblefor the majority of damage. The Cali-fornia vole,M. californicus, is the mostwidespread vole in the state, found inthe Owens and Central valleys andnearly the entire length of the coastalrange. The montane vole,M. montanus,inhabits northeastern California andthe eastern Sierra slope. Voles usuallydont invade homes and shouldnt beconfused with the house mouse,Musmusculus.

Voles are intriguing, small mammals,because some populations regularly gothrough cycles of low to high numberswith occasional, sudden increases thatcan send numbers soaring up to severalthousand per acre.

IDENTIFICATION

Voles are mouselike rodents some-what similar in appearance to pocketgophers (Fig. 1). They have a compact,heavy body, short legs, a short-furred

tail, small eyes, and partially hiddenears. Their long, coarse fur is blackishbrown to grayish brown. When fullygrown they can measure 5 to 8 incheslong, including the tail.

Although voles spend considerabletime aboveground and you occasion-ally can see them scurrying about,they spend most of their time belowground in their burrow system. Theclearest signs of their presence arethe well-traveled, aboveground run-ways that connect burrow openings

(Fig. 2). A protective layer of grass orother ground cover usually hides therunways. The maze of runways leadsto multiple burrow openings that are

each about 1 1/2 to 2 inches in diameter.

You can locate the runways by pulling

back overhanging ground cover. Freshclippings of green grass and greenish-

colored droppings about 3/16 inch longin the runways and near the burrowsare further evidence of voles. With age,the droppings lose the green coloringand turn brown or gray.

BIOLOGY AND BEHAVIOR

Voles are active day and night, year-round. Youll normally nd them inareas with dense vegetation. Volesdig many short, shallow burrows andmake underground nests of grass,stems, and leaves. In areas with win-ter snow, voles will burrow in andthrough the snow to the surface.

Several adults and young can occupy aburrow system. The size of the burrowsystem and foraging area varies withhabitat quality, food supply, and popu-lation levels, but in most cases it is nomore than a few hundred square feet.

Vole numbers uctuate from year toyear, and under favorable conditions,

their populations can increase rapidly.In some areas their numbers are cycli-cal, reaching peak numbers every 3 to6 years before dropping back to lowlevels. Voles can breed any time of year,but the peak breeding period is spring.Voles are extremely prolic, with fe-males maturing in 35 to 40 days andhaving 5 to 10 litters per year. Littersize ranges from 3 to 6 young. How-ever, voles seldom live longer than 12months.

Voles are mostly herbivorous, feeding

on a variety of grasses, herbaceousplants, bulbs, and tubers. They eatbark and roots of trees, usually in fal lor winter. Voles store seeds and otherplant matter in underground chambers.

Voles are poor climbers and usuallydont enter homes or other buildings.

Instead, they inhabit wildlands or crop-lands adjacent to buildings or gardensand landscaped sites with protectiveground cover. Most problems aroundhomes and gardens occur during out-

breaks of vole populations.

DAMAGE

Voles cause damage by feeding on awide range of garden plants includingartichoke, beet, Brussels sprouts, cab-

bage, carrot, cauliower, celery, lettuce,spinach, sweet potato, tomato, and

turnip. They also can damage turf andother landscape plantings such as lil-ies and dichondra. Voles will gnaw thebark of fruit trees including almond,apple, avocado, cherry, citrus, and olive.

Integrated Pest Management for Home Gardeners and Landscape Professionals

Voles(MeadowMice)

Figure 1. Vole (meadow mouse).

Figure 2. Meadow mouse runways con-nect numerous, shallow burrows.


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Vole damage to tree trunks normallyoccurs from a few inches abovegroundto a few inches below ground. If thedamage is below ground, you will needto remove soil from the base of thetree to see it. Although voles are poorclimbers, if they can climb onto low-hanging branches, they can cause dam-age higher up on trees as well.

Gnaw marks about 1/8 inch wide and3/8 inch long in irregular patches andvarious angles along with other signsincluding droppings, runways, and

burrows indicate vole damage. If volesgnaw completely around the trunk orroots, it will disrupt the trees ow ofnutrients and water, a process knownas girdling. Girdling damage on trunks

and roots can kill trees. Signs of partialtrunk or root girdling can include aprolonged time before young trees bearfruit, reduced fruit yield, abnormalyellowish leaf color, and overall poorvigor. Where snow cover is present,damage to trees can extend a foot ormore up the trunk. Damage that occurs

beneath snow cover often escapes no-tice until it is too late.

LEGAL STATUS

The California Fish and Game Codeclassies voles as nongame mammals,

meaning if voles are injuring or threat-ening growing crops or other property,the owner or tenant of the property haspermission to control them at any timeand in any legal manner.

MANAGEMENT

To prevent vole damage, you need tomanage the population in your area

before it reaches high numbers. Youoften can achieve this by removing orreducing the vegetative cover, makingthe area unsuitable to voles. Removing

cover also makes detecting voles andother rodents easier. Once vole num-

bers begin to increase rapidly, the dam-age they do to ornamental and gardenplants and to trees can be quite severe.

Monitoring Guidelines

Be alert for the presence of voles. Lookfor fresh trails in the grass, burrows,droppings, and evidence of feeding in

the garden and surrounding area. Payparticular attention to adjacent areasthat have heavy vegetation, becausesuch areas are likely sources of inva-sions.

Habitat ModifcationOne way to effectively deter vole popu-lations is to make the habitat less suit-able to them. Weeds, heavy mulch, anddense vegetative cover encourage voles

by providing food and protection frompredators and environmental stresses.If you remove this protection, theirnumbers will decline.

You can reduce the area from whichvoles can invade gardens or land-scaped areas by regularly mowing,

spraying with herbicides, grazing, ortilling grassy areas along ditch banks,right-of-ways, or eld edges adjacentto gardens. If feasible, weed-free stripscan serve as buffers around areasrequiring protection. The wider thecleared strip, the less apt voles will

be to cross and become established ingardens. A minimum width of 15 feetis recommended, but even that canbe ineffect ive when vole numbers arehigh. A 4-foot-diameter circle aroundthe base of young trees or vines thatis free of vegetation or a buffer strip 4

feet or more along a row of trees canreduce problems, because voles prefernot to feed in the open.

Exclusion

Wire fences at least 12 inches above

the ground with a mesh size of1/4 inchor smaller will help to exclude volesfrom the entire garden. These fenceseither can stand alone or be attached tothe bottom of an existing fence (Fig. 3).Bury the bottom edge of the fence 6 to10 inches to prevent voles from tunnel-

ing beneath it. A weed-free barrier onthe outside of the fence will increase itseffectiveness.

You can protect young trees, vines, andornamentals from girdling by usingcylinders made from hardware cloth,sheet metal, or heavy plastic that sur-round the trunk (Fig. 4). Support orbrace these devices, so they cant be

pushed over or pressed against thetrunk. Also make sure they are wideenough to allow for tree growth and, inareas with snow, are tall enough to ex-tend above snow level. Bury the bottomof the protective device below the soil

Figure 3. Small mesh wire fence.

Figure 4. A plastic cylinder protects

the trunk of this young tree from voledamage.


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surface to prevent voles from diggingbeneath it. You can cut out both endsof individual milk cartons, tin cans, orplastic soda bottles and t them oversmall plants. Youll want to frequentlycheck protective devices to make suremeadow mice havent gnawed throughor dug beneath the cylinders and arehiding inside the tree guard while theyfeed on the tree.

Trapping

When voles arent numerous or whenthe population is concentrated in asmall area, trapping can be effective.Use a sufcient number of traps to con-trol the population. For a small gardena dozen traps is probably the mini-mum number required, but for larger

areas, you might need 50 or more. Youcan use a simple, wooden mouse trap

baited with a peanut butter-oatmealmixture or apple slices, although oftenyou wont need to use bait, becausevoles will trigger the trap as they passover it.

Trap placement is crucial. Voles seldomstray from their runways, so set trapsalong these routes. Look for burrowsand runways in grass or mulch in ornear the garden. Place the traps at right

angles to the runways with the trig-ger end in the runway. Examine trapsdaily, removing dead voles or reset-ting sprung traps as needed. Continueto trap in one location until you stopcatching voles then move the trap to anew location 15 to 20 feet away. Destroyold runways or burrows with a shovelor rototiller to deter new voles from im-migrating to the site.

Bury dead voles, or place them inplastic bags in the trash. Because volescan carry infectious pathogens or

parasites, dont handle them withoutrubber gloves; you can use a plastic

bag slipped over your hand and armas a glove. Once you have removed thevole from the trap, hold it with yourbagged hand and turn the bag insideout while slipping it off your arm andhand. Be sure to keep small childrenand pets out of areas where you haveset traps.

Baiting

When voles are numerous or whendamage occurs over large areas, toxic

baits can be the quickest and mostpractical means of control. Take neces-

sary measures to ensure the safety ofchildren, pets, and nontarget animals,and follow all product label instruc-tions carefully.

Anticoagulants, often referred to asmultiple-feeding baits, interfere withan animals blood-clotting mechanisms,eventually leading to death. They prob-ably are the safest type of rodent baitfor use around homes and gardens,because they are slow acting, must beconsumed during a period of 5 or moredays to be effective, and have an ef-

fective antidote, vitamin K1, making itsafer to use around children and pets.Anticoagulant baits are available atmany county agriculture commission-ers ofces as well as at retail stores.

You cant use some anticoagulants suchas brodifacoum and bromadiolone

because of the potential risk they poseto predators such as cats and dogs.These are common over-the-counterrat and mouse poisons. Check the labelcarefully to ensure it lists that the baitis suitable for use on voles or meadow

mice.

Because the pest must feed on antico-agulant baits during a period of 5 days,the bait must be available until the volepopulation is under control. Usuallybaiting every other day for a total of 3applications is effective. As with trap-ping, bait placement is very important.Place the recommended amount of baitin runways or next to burrows, so voleswill nd it during their normal travels.Generally, spot treatingplacing baitin a specic place, such as a runway

is the preferred method of baiting, butin areas of heavy ground cover or ifthe area you are treating is quite large,broadcasting might be a better optionif the label allows it. When broadcast-ing bait, be sure to spread it evenlyover the infested area. If you use thistechnique, you probably will have tobroadcast every other day for a total of3 or 4 applications.

Repellents

Commercial repellents are available forprotecting plants from voles, but theireffectiveness is questionable and theiruse often isnt practical. You must ap-

ply them before damage occurs. Volesusually damage plants at or just be-neath the soil surface, making adequatecoverage difcult or impossible. Dontapply repellents to food crops unlessthe product label species such use.

Natural Control

Many predators including coyotes, foxes,badgers, weasels, cats, gulls, and espe-cially hawks and owls eat voles. How-ever, in most cases predators cant keepvole populations below damaging levels.Many predators simply dont hunt closeto homes and gardens where control isneeded. Most predators have a broad-

based diet and readily shift to alternativeprey when the number of voles declines.Predators rarely, if ever, take every lastvole; thus, a residual population remains.With their extremely high reproductivepotential, any remaining voles could re-populate an area in a short period. Withthis potential for severe damage, a hom-eowner or gardener cant afford to waitfor a predator to appear but must takeimmediate action to prevent the loss of

valuable plantings. Effective, immediateaction usually involves baiting or trap-ping and habitat modication.

As with all animals, natural constraintslimit vole numbers. Because popula-tions wont increase indenitely, onealternative is to do nothing, and letnature limit the voles. Experience hasshown, however, that around homesand gardens the natural populationpeak is too high, and damage will beabove tolerable limits.

Other Control MethodsBurrow fumigants such as gas cartridg-es arent effective for controlling voles,

because their burrow system is shallowand has numerous open holes. Commer-cial pest control operators can use thefumigant aluminum phosphide undervery limited conditions. Electromag-netic or ultrasonic devices and oodingalso are ineffective against voles.


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REFERENCES

Giusti, G. A. 1994. Protecting Your Gar-den from Animal Damage. San Ramon:The Solaris Group.

Ingles, L. G. 1965.Mammals of the PacicStates: California, Oregon, Washington.Stanford: Stanford Univ. Press.

Johnson, M. L., and S. Johnson. 1982.Voles. In J. A. Chapman and G. A. Feld-hamer, eds. Wild Mammals of NorthAmerica: Biology, Management, Economics.

Baltimore: Johns Hopkins Univ. Press.

pp. 326354.

OBrien, J. M. 1994. Voles. In S. E. Hyg-

nstrom, R. M. Timm, and G. E. Larson,

eds. Prevention and Control of Wildlife

Damage, Vol. 1. Lincoln: Univ. Neb.

Coop. Ext. pp. B.177182.

Salmon, T. P., D. A. Whisson, and R. E.

Marsh. 2006. Wildlife Pest Control around

Gardens and Homes. 2nd ed. Oakland: Univ.

Calif. Agric. Nat. Res. Publ. 21385.v

AUTHORS:T. P. Salmon, UC Cooperative

Extension, San Diego Co.; and W. P. Gore-

nzel, UC Cooperative Extension, San Diego

Co.

TECHNICAL EDITOR: M. L. Flint

EDITOR: M. L. Fayard

ILLUSTRATIONS:Figs. 1-2 and 4, J. K.

Clark; and Fig. 3, W. P. Gorenzel.

This and other Pest Notes are available at

www.ipm.ucdavis.edu.

For more information, contact the University of

California Cooperative Extension ofce in yourcounty. See your telephone directory for addresses

and phone numbers, or visit http://ucanr.org/ce.cfm.University of California

Agriculture and Natural Resources Program

Produced by UC Statewide

Integrated Pest Management Program

University of California, Davis, CA 95616

University of California scientists and otherqualied professionals have anonymously peerreviewed this publication for technical accuracy. TheANR Associate Editor for Urban Pest Managementmanaged this review process.

To simplify information, trade names of products

have been used. No endorsement of named productsis intended, nor is criticism implied of similar productsthat are not mentioned.

This material is partially based upon worksupported by the Extension Service, U.S. Departmentof Agriculture, under special project Section 3(d),Integrated Pest Management.

WARNING ON THE USE OF CHEMICALSPesticides are poisonous. Always read and carefully follow all precautions and safety recommendations

given on the container label. Store all chemicals in the original, labeled containers in a locked cabinet or shed,away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock.

Pesticides applied in your home and landscape can move and contaminate creeks, rivers, and oceans.Conne chemicals to the property being t reated. Avoid drift onto neighboring properties, especially gardenscontaining fruits or vegetables ready to be picked.

Do not place containers containing pesticide in the trash or pour pesticides down the sink or toilet. Either usethe pesticide according to the label, or take unwanted pesticides to a Household Hazardous Waste Collectionsite. Contact your county agricultural commissioner for additional information on safe container disposal andfor the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containersby following label directions. Never reuse or burn the containers or dispose of them in such a manner thatthey may contaminate water supplies or natural waterways.

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Voles (Meadow Mice)