Voles and Lemmings
Description and Identification
Several species of voles are found in Illinois. These include the prairie vole (Microtus ochrogaster), meadow vole (Microtus pennsylvanicus), and woodland vole (Microtus pinetorum). The southern bog lemming (Synaptomys cooperi) also occurs in Illinois. Voles and lemmings are small, stocky rodents. They are approximately 4¼ to 7 inches in length and weigh 25 to 50 grams, depending on the species. They have grizzled brown to reddish-brown fur, short legs, and furred ears. They can be distinguished from mice by their stocky body shape and short tails (typically less than one-third of the length of the body). Meadow voles and woodland voles are the species most likely to cause problems in Illinois.
Meadow voles inhabit grasslands in low-lying areas or near stream, lakes, or swamps. Prairie voles live in upland grasslands, fallow fields, and fencerows and typically avoid wooded areas. Woodland voles inhabit deciduous forests and grassy areas near woody areas. Southern bog lemmings use a variety of grassland habitats, but use habitats more like those used by the meadow vole.
Distribution and Abundance
Prairie and woodland voles are common throughout Illinois. The meadow vole is common in the northern two-thirds of the state. Southern bog lemmings have a statewide distribution but are less common than the other three species.
Female voles can have several litters during a year. Meadow and prairie voles have an average of three to five young per litter. Woodland voles average two to three young per litter, and southern bog lemmings produce an average of three to four young per litter. Females can begin breeding at three weeks of age.
The size of vole populations can fluctuate widely over many years.
Voles are herbivores (eat plants). They feed heavily on grasses, sedges, alfalfa, goldenrod, clover, and plantain. They will also eat grains, seeds, berries, bulbs, and occasionally insects or snails. When other foods are limited, voles will eat bark from the base of trees and shrubs. This often occurs during the winter in Illinois.
Voles build shallow, underground burrow systems with many entrances. Meadow voles and prairie voles will create surface runways (small trail systems) through the grass, while woodland voles build surface runways just under the leaf litter. These runways are approximately one to two inches wide, and nearby vegetation are often clipped to the ground. The stems of vegetation are cut cleanly on a 45° angle. Meadow voles sometimes build a nest of grass above ground, whereas the other species build nests below ground.
Voles are active during the day and night, although they are most active at night. Even when active during the day, voles are secretive and seldom seen, because they are hidden beneath a dense herbaceous vegetation cover.
Voles have a very short lifespan, because they are a major food source for foxes, hawks, snakes, and other predators of small mammals. Most voles live less than one year. Life expectancy depends upon food availability and other factors.
Damage Prevention and Control Measures
Voles are more often a problem in agricultural fields and orchards than in the urban landscape. Young orchard trees are particularly susceptible to vole damage during the winter when voles feed on bark and tree roots. Voles can kill trees if they girdle them or cause extensive root damage.
However, voles can become a problem for homeowners, if they severely damage garden or landscaping plants. Voles may feed on bulbs, tubers, and corms, especially during the winter. Because voles often use the tunnel systems of moles, moles are sometimes blamed for damage actually caused by voles.
Voles may clip grass and create surface runways in lawns under a layer of snow. The trail systems disappear quickly once the grass begins to grow in the spring and the lawn is not harmed.
Rabbits will also gnaw on bark, especially during the winter. To determine whether or not voles are causing the damage, look for irregular gnaw marks and note their width. Voles gnaw on bark from various angles and make marks approximately 1/8 inch wide, 3/8 inch long, and 1/16 inch deep. Rabbit gnaw marks are wider and longer, and rabbits often clip off small branches at a 45° angle.
Habitat modification is the best way to control vole damage. Keeping grass mowed short will reduce food resources and cover, that will reduce vole numbers in the area. Mulch should be kept at least three feet away from the base of trees.
Small gardens, flowerbeds, or favorite plants can be protected from vole damage by using an underground barrier. Bury one-quarter inch or less mesh hardware cloth six to eight inches into the soil around the area you wish to protect.
Surrounding trees or shrubs with hardware cloth or a tree protector that has openings one-quarter inch or less can protect them. The protector must be flush with the ground so that the voles cannot squeeze in underneath the protector.
Thiram applied to roots or tubers before planting may help protect plants from vole damage, but this strategy provides only short-term protection.
Zinc phosphide baits and anticoagulants (Chlorophacinone and Diphacinone) may be used to control voles in Illinois. The zinc phosphide baits should be placed in runways and burrow openings. The baits should not be broadcast, because they are potentially hazardous to ground-feeding birds. Toxicants may only be used by licensed pesticide applicators. Read and follow the instructions on the product label.
Recommendations for the control of voles in Illinois' commercial apple orchards are available by clicking the icon. The common and scientific names of the pine vole (Pitymys pinetorum) were changed to woodland vole (Microtus pinetorum) since the article was written.
Mouse snap traps can be used to remove a small number of voles. However, due to their reproductive capabilities, it is typically ineffective to trap voles over a large area. The traps should be set perpendicular to the vole runway with the trigger end placed in the runway.
Public Health Concerns
Voles help aerate the soil through their burrowing activities. They are also a major food resource for predators such as foxes, coyotes, bobcats, weasels, owls, hawks, snakes, and others.
The Illinois Wildlife Code does not protect voles. They may be removed without a permit.