Two species of voles, the California vole and montane vole, are responsible for the majority of damage in California. Voles are small, mouse-like rodents that live in extensive underground burrow systems. Their populations fluctuate cyclically, sometimes reaching outbreak levels of thousands per acre. Voles cause damage by feeding on plants, trees, and shrubs in gardens and landscapes. Effective management of voles involves habitat modification to remove protective ground cover, trapping, and the use of anticoagulant baits.
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Voles (Meadow Mice) Integrated Pest Management
1. Voles (Meadow Mice)
Integrated Pest Management for Home Gardeners and Landscape Professionals
Six species of voles from the genus Mi-crotus
occur in California. Collectively
they are called either meadow mice
or voles. Two species are responsible
for the majority of damage. The Cali-fornia
vole, M. californicus, is the most
widespread vole in the state, found in
the Owens and Central valleys and
nearly the entire length of the coastal
range. The montane vole, M. montanus,
inhabits northeastern California and
the eastern Sierra slope. Voles usually
don’t invade homes and shouldn’t be
confused with the house mouse, Mus
musculus.
Voles are intriguing, small mammals,
because some populations regularly go
through cycles of low to high numbers
with occasional, sudden increases that
can send numbers soaring up to several
thousand per acre.
IDENTIFICATION
Voles are mouselike rodents some-what
similar in appearance to pocket
gophers (Fig. 1). They have a compact,
heavy body, short legs, a short-furred
tail, small eyes, and partially hidden
ears. Their long, coarse fur is blackish
brown to grayish brown. When fully
grown they can measure 5 to 8 inches
long, including the tail.
Although voles spend considerable
time aboveground and you occasion-ally
can see them scurrying about,
they spend most of their time below
ground in their burrow system. The
clearest signs of their presence are
the well-traveled, aboveground run-ways
that connect burrow openings
(Fig. 2). A protective layer of grass or
other ground cover usually hides the
runways. The maze of runways leads
to 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. Fresh
clippings of green grass and greenish-colored
droppings about 3/16 inch long
in the runways and near the burrows
are further evidence of voles. With age,
the droppings lose the green coloring
and turn brown or gray.
BIOLOGY AND BEHAVIOR
Voles are active day and night, year-round.
You’ll normally find them in
areas with dense vegetation. Voles
dig many short, shallow burrows and
make underground nests of grass,
stems, and leaves. In areas with win-ter
snow, voles will burrow in and
through the snow to the surface.
Several adults and young can occupy a
burrow system. The size of the burrow
system and foraging area varies with
habitat quality, food supply, and popu-lation
levels, but in most cases it is no
more than a few hundred square feet.
Vole numbers fluctuate from year to
year, and under favorable conditions,
their populations can increase rapidly.
In some areas their numbers are cycli-cal,
reaching peak numbers every 3 to
6 years before dropping back to low
levels. Voles can breed any time of year,
but the peak breeding period is spring.
Voles are extremely prolific, with fe-males
maturing in 35 to 40 days and
having 5 to 10 litters per year. Litter
size ranges from 3 to 6 young. How-ever,
voles seldom live longer than 12
months.
Voles are mostly herbivorous, feeding
on a variety of grasses, herbaceous
plants, bulbs, and tubers. They eat
bark and roots of trees, usually in fall
or winter. Voles store seeds and other
plant matter in underground chambers.
Figure 1. Vole (meadow mouse).
Figure 2. Meadow mouse runways con-nect
numerous, shallow burrows.
Voles are poor climbers and usually
don’t enter homes or other buildings.
Instead, they inhabit wildlands or crop-lands
adjacent to buildings or gardens
and landscaped sites with protective
ground cover. Most problems around
homes and gardens occur during out-breaks
of vole populations.
DAMAGE
Voles cause damage by feeding on a
wide range of garden plants including
artichoke, beet, Brussels sprouts, cab-bage,
carrot, cauliflower, celery, lettuce,
spinach, sweet potato, tomato, and
turnip. They also can damage turf and
other landscape plantings such as lil-ies
and dichondra. Voles will gnaw the
bark of fruit trees including almond,
apple, avocado, cherry, citrus, and olive.
PEST NOTES Publication 7439
University of California
Statewide Integrated Pest Management Program
Agriculture and Natural Resources
June 2010
2. June 2010 Voles (Meadow Mice)
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Vole damage to tree trunks normally
occurs from a few inches aboveground
to a few inches below ground. If the
damage is below ground, you will need
to remove soil from the base of the
tree to see it. Although voles are poor
climbers, 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 and
3/8 inch long in irregular patches and
various angles along with other signs
including droppings, runways, and
burrows indicate vole damage. If voles
gnaw completely around the trunk or
roots, it will disrupt the tree’s flow of
nutrients and water, a process known
as girdling. Girdling damage on trunks
and roots can kill trees. Signs of partial
trunk or root girdling can include a
prolonged time before young trees bear
fruit, reduced fruit yield, abnormal
yellowish leaf color, and overall poor
vigor. Where snow cover is present,
damage to trees can extend a foot or
more 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 Code
classifies voles as nongame mammals,
meaning if voles are injuring or threat-ening
growing crops or other property,
the owner or tenant of the property has
permission to control them at any time
and in any legal manner.
MANAGEMENT
To prevent vole damage, you need to
manage the population in your area
before it reaches high numbers. You
often can achieve this by removing or
reducing the vegetative cover, making
the area unsuitable to voles. Removing
cover also makes detecting voles and
other rodents easier. Once vole num-bers
begin to increase rapidly, the dam-age
they do to ornamental and garden
plants and to trees can be quite severe.
Monitoring Guidelines
Be alert for the presence of voles. Look
for fresh trails in the grass, burrows,
droppings, and evidence of feeding in
the garden and surrounding area. Pay
particular attention to adjacent areas
that have heavy vegetation, because
such areas are likely sources of inva-sions.
Habitat Modification
One way to effectively deter vole popu-lations
is to make the habitat less suit-able
to them. Weeds, heavy mulch, and
dense vegetative cover encourage voles
by providing food and protection from
predators and environmental stresses.
If you remove this protection, their
numbers will decline.
You can reduce the area from which
voles can invade gardens or land-scaped
areas by regularly mowing,
spraying with herbicides, grazing, or
tilling grassy areas along ditch banks,
right-of-ways, or field edges adjacent
to gardens. If feasible, weed-free strips
can serve as buffers around areas
requiring protection. The wider the
cleared strip, the less apt voles will
be to cross and become established in
gardens. A minimum width of 15 feet
is recommended, but even that can
be ineffective when vole numbers are
high. A 4-foot-diameter circle around
the base of young trees or vines that
is free of vegetation or a buffer strip 4
feet or more along a row of trees can
reduce problems, because voles prefer
not to feed in the open.
Exclusion
Wire fences at least 12 inches above
the ground with a mesh size of 1/4 inch
or smaller will help to exclude voles
from the entire garden. These fences
either can stand alone or be attached to
the bottom of an existing fence (Fig. 3).
Bury the bottom edge of the fence 6 to
10 inches to prevent voles from tunnel-ing
beneath it. A weed-free barrier on
the outside of the fence will increase its
effectiveness.
You can protect young trees, vines, and
ornamentals from girdling by using
cylinders made from hardware cloth,
sheet metal, or heavy plastic that sur-round
the trunk (Fig. 4). Support or
brace these devices, so they can’t be
Figure 3. Small mesh wire fence.
Figure 4. A plastic cylinder protects
the trunk of this young tree from vole
damage.
pushed over or pressed against the
trunk. Also make sure they are wide
enough to allow for tree growth and, in
areas with snow, are tall enough to ex-tend
above snow level. Bury the bottom
of the protective device below the soil
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surface to prevent voles from digging
beneath it. You can cut out both ends
of individual milk cartons, tin cans, or
plastic soda bottles and fit them over
small plants. You’ll want to frequently
check protective devices to make sure
meadow mice haven’t gnawed through
or dug beneath the cylinders and are
hiding inside the tree guard while they
feed on the tree.
Trapping
When voles aren’t numerous or when
the population is concentrated in a
small area, trapping can be effective.
Use a sufficient number of traps to con-trol
the population. For a small garden
a dozen traps is probably the mini-mum
number required, but for larger
areas, you might need 50 or more. You
can use a simple, wooden mouse trap
baited with a peanut butter-oatmeal
mixture or apple slices, although often
you won’t need to use bait, because
voles will trigger the trap as they pass
over it.
Trap placement is crucial. Voles seldom
stray from their runways, so set traps
along these routes. Look for burrows
and runways in grass or mulch in or
near the garden. Place the traps at right
angles to the runways with the trig-ger
end in the runway. Examine traps
daily, removing dead voles or reset-ting
sprung traps as needed. Continue
to trap in one location until you stop
catching voles then move the trap to a
new location 15 to 20 feet away. Destroy
old runways or burrows with a shovel
or rototiller to deter new voles from im-migrating
to the site.
Bury dead voles, or place them in
plastic bags in the trash. Because voles
can carry infectious pathogens or
parasites, don’t handle them without
rubber gloves; you can use a plastic
bag slipped over your hand and arm
as a glove. Once you have removed the
vole from the trap, hold it with your
“bagged” hand and turn the bag inside
out while slipping it off your arm and
hand. Be sure to keep small children
and pets out of areas where you have
set traps.
Baiting
When voles are numerous or when
damage occurs over large areas, toxic
baits can be the quickest and most
practical means of control. Take neces-sary
measures to ensure the safety of
children, pets, and nontarget animals,
and follow all product label instruc-tions
carefully.
Anticoagulants, often referred to as
multiple-feeding baits, interfere with
an animal’s blood-clotting mechanisms,
eventually leading to death. They prob-ably
are the safest type of rodent bait
for use around homes and gardens,
because they are slow acting, must be
consumed during a period of 5 or more
days to be effective, and have an ef-fective
antidote, vitamin K1, making it
safer to use around children and pets.
Anticoagulant baits are available at
some county agriculture commission-ers’
offices as well as at retail stores.
You can’t use some anticoagulants such
as brodifacoum and bromadiolone be-cause
of the potential risk they pose to
predators such as cats and dogs. Check
the label carefully to ensure it lists that
the bait is 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 vole
population is under control. Usually
baiting every other day for a total of 3
applications is effective. As with trap-ping,
bait placement is very important.
Place the recommended amount of bait
in runways or next to burrows, so voles
will find it during their normal travels.
Generally, spot treating—placing bait
in a specific place, such as a runway—
is the preferred method of baiting, but
in areas of heavy ground cover or if
the area you are treating is quite large,
broadcasting might be a better option
if the label allows it. When broadcast-ing
bait, be sure to spread it evenly
over the infested area. If you use this
technique, you probably will have to
broadcast every other day for a total of
3 or 4 applications.
Repellents
Commercial repellents are available for
protecting plants from voles, but their
effectiveness is questionable and their
use often isn’t practical. You must ap-ply
them before damage occurs. Voles
usually damage plants at or just be-neath
the soil surface, making adequate
coverage difficult or impossible. Don’t
apply repellents to food crops unless
the product label specifies 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 can’t keep
vole populations below damaging levels.
Many predators simply don’t hunt close
to homes and gardens where control is
needed. Most predators have a broad-based
diet and readily shift to alternative
prey when the number of voles declines.
Predators rarely, if ever, take every last
vole; thus, a residual population remains.
With their extremely high reproductive
potential, any remaining voles could re-populate
an area in a short period. With
this potential for severe damage, a hom-eowner
or gardener can’t afford to wait
for a predator to appear but must take
immediate action to prevent the loss of
valuable plantings. Effective, immediate
action usually involves baiting or trap-ping
and habitat modification.
As with all animals, natural constraints
limit vole numbers. Because popula-tions
won’t increase indefinitely, one
alternative is to do nothing, and let
nature limit the voles. Experience has
shown, however, that around homes
and gardens the natural population
peak is too high, and damage will be
above tolerable limits.
Other Control Methods
Burrow fumigants such as gas cartridg-es
aren’t effective for controlling voles,
because their burrow system is shallow
and has numerous open holes. Commer-cial
pest control operators can use the
fumigant aluminum phosphide under
very limited conditions. Electromag-netic
or ultrasonic devices and flooding
also are ineffective against voles.
4. June 2010 Voles (Meadow Mice)
REFERENCES
Giusti, G. A. 1994. Protecting Your Gar-den
from Animal Damage. San Ramon:
The Solaris Group.
Ingles, L. G. 1965. Mammals of the Pacific
States: 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 North
America: Biology, Management, Economics.
◆ 4 of 4 ◆
Baltimore: Johns Hopkins Univ. Press.
pp. 326–354.
O’Brien, 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.177–182.
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 office in your
county. See your telephone directory for addresses
and phone numbers, or visit http://ucanr.org/ce.cfm.
University of California scientists and other
qualified professionals have anonymously peer
reviewed this publication for technical accuracy. The
ANR Associate Editor for Urban Pest Management
managed this review process.
To simplify information, trade names of products
have been used. No endorsement of named products
is intended, nor is criticism implied of similar products
that are not mentioned.
This material is partially based upon work
supported by the Extension Service, U.S. Department
of Agriculture, under special project Section 3(d),
Integrated Pest Management.
Produced by UC Statewide
Integrated Pest Management Program
University of California, Davis, CA 95616
University of California
Agriculture and Natural Resources Program
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