Going On Vole Patrol

But in this case, the mysterious “lawn mower” is probably a vole. Also known as “meadow mice,” voles are small rodents belonging to the family Arvicolidae. The word vole refers to “field”— earlier uses of the word were “vole-mouse,” and eventually simply “vole.” Calling voles “field mice” is ambiguous and should be avoided because the house mouse, the deer mouse, the white-footed mouse, the vole, and even the shrew all inhabit fields, and all are sometimes generically referred to as field mice.

Voles are mostly herbivorous in their feeding. They feed on the fresh new grass shoots, clipping the grass off at the base and “harvesting” a path through the grass. During long winters in areas of snow, voles will remain active beneath the snow, and will attack the trunks and roots of various ornamental trees and shrubs for food. Voles are an occasional nuisance to homeowners, landscapers, and commercial properties such as golf courses and commercial office complexes.

TELLTAIL CHARACTERISTICS. Voles are stocky, rounded rodents with short tails, short ears and a blunted nose. The legs are short and the tail is sparse of hairs. The length of the body and tail varies according to the species, but most voles measure between 4 and 7 inches, with tails ranging from ¾ to 2¾ inches long. Mature meadow voles are chestnut-brown mixed with black on the back. Young voles may be darker than adults, with nearly black feet. In North America, there are 19 species of voles, but the Meadow vole, Microtus pennsyl-vanicus, is the most numerous and the most likely to be encountered.

Voles are sometimes confused with shrews, but voles are members of the rodent order, while shrews (and moles) belong to the order Insectivora. Insectivora are characterized in part by their diet of insects, earthworms, and a wide assortment of other invertebrates. Shrews do not have visible ears, and their eyes are difficult to locate among their fur. Moreover, the shrew is a small, slim animal with a head that appears to come to a point.

Although this point might seem academic to the practicing PCO, it is important to understand the difference. For example, voles, being herbivores, may respond well to various seeds and grains as natural food items in the same manner as do rats and mice. Moles and shrews on the other hand do not eat grains as readily as do the rodents, and are therefore poor candidates for grain-based toxicants.

Voles are among the most prolific mammals on earth. Meadow voles have been recorded producing up to 17 consecutive litters in one year, resulting in an amazing 83 offspring. The typical vole litter contains three to six pups, but the high reproductive potential of voles is offset dramatically by a high mortality rate. The vole is probably the most important item in the food chain among secondary consumers. Many mammalian carnivores such as dogs, coyotes, cats, raccoons, and skunks eagerly eat moles, as do snakes. Cats and dogs in suburbia are often seen stalking voles in the grass.

Voles are also the most common food source for predatory birds. As a result, mortality rates for vole populations can range as high as 88%. Understandably then, many voles live for only a few months before succumbing to one predator or another. In some areas, vole populations may be cyclic with outbreaks occurring every four to six years.

The meadow vole constructs well-defined, visible surface runways through turf areas measuring about 1½ to 2 inches in width. The runways are formed by a combination of the vole eating the grass blades and its constant traveling over the runways. Additionally, some parts of the runway become dirt-bare as a result of the vole spreading excavated dirt from the burrow system in the runway. It is these paths that often are responsible for homeowners calling pest management professionals beginning in March and April and inquiring as to the responsible animal.

Voles are active for intermittent periods during the day and night. Typically they make quick visits from the burrow through their runways and back, making about 15 to 20 forays from the nest, each lasting only about 10 minutes. Thus, people rarely see the vole itself. Most people realize they have voles only as a result of the damage to their turf or landscaping. Home ranges may be as large as 1½ acres, but in typical residential landscaping, if vegetation is abundant, they may range only 30 to 50 feet out from the protection of cover.

VOLE MANAGEMENT. Voles, an exterior pest, enter buildings only incidentally. They do not breed indoors. For buildings in areas of high vole pressure, such as warehouses surrounded by fields, the building should be kept rodent-proofed as is done for the commensal rodents.

Because voles are usually associated with dense cover, proper landscaping reducing the attractive cover will reduce the severity of vole infestations. Heavy low-lying vegetation should be pruned to expose the undercover. Vegetation and weed control programs are a critical part of vole management. If the conditions responsible for the vole infestation are not corrected, removing voles via trapping or baiting is likely to produce only short-term results, as voles are extremely prolific when they have abundant food and cover. For most residential situations, turf and landscape damage from damage from voles is due to minor infestations, e.g. one or two families of voles (six to 12 animals). These infestations can be eliminated using expanded trigger mousetraps. Indoors, traps can be placed along walls as would be done for house mice.

Outside, traps can be placed at the beginning of the runways a couple of inches from the burrows beneath the natural cover. If this area is not accessible, traps can also be set directly in the runways in the turf.

Traps need not be baited. Some professionals, however, feel that smudges of peanut butter mixed with oatmeal produce better results. If traps need to be set in open areas, they should be placed beneath the overturned bases of non-tamper-resistant plastic bait stations, or in cardboard boxes, etc. to avoid trapping non-target animals such as shrews, small birds or the paws or nose of the family cat or dog. For large infestations of voles (especially around commercial accounts), rodenticide baiting programs are a more practical and cost-effective program than traps.

Rodenticide baits used against the commensal rodents are effective against voles. Currently, zinc phosphide and a few of the anticoagulant baits are registered against voles, mostly for ornamental landscaping, parks and golf courses. Some of the bait registrations vary among different parts of the country. Because voles do not venture far from their established paths to locate food, the key to effective baiting lies with a thorough inspection to determine the high activity areas of the voles, and then locating the baits in these areas. Baits should be placed inside bait stations to exclude non-target animals. Openings of the bait stations should intersect the runways. Depending on the particular rodenticide, the bait may also be inserted carefully and directly into the vole burrows openings. All treated burrows and exterior stations should be flagged to ensure recovering all stations upon program completion. All treated burrows should also be collapsed at the end of the program, and re-checked periodically for recurring invasions. The baits should never be placed loosely within the exposed runways. In cases where it is desirable to avoid using pesticides outdoors for large infestations, traps can be used, but large numbers of traps will be required to reduce the population. Although this is more labor intensive, and thus more expensive, some clients prefer this approach to minimize the danger of possible secondary hazards to predaceous hawks and owls feeding on poisoned voles. Multiple catch traps can also be effective if set in the major runways.

All in all, it pays to be proactive when it comes to voles around properties. While working around the exterior of buildings, keep an eye open for the vole runways through the turf. With a mammal that reproduces this fast, PCOs can’t afford to let them get to first base.