Are Voles Munching Your Garden?
by Neil Soderstrom

While inspecting her garden one spring, Mary Ann McGourty noticed a few empty patches here and there and thought, "Oh, well, that plant didn't make it through the winter." Next she came upon a wilting dianthus. "When I gave it a tug," she said, "I was holding what felt like a toupée in my hand. And other of my established plants with fleshy roots were disappearing too—iris, alliums, hostas, ornamental grasses—as well as newly planted things." Mary Ann suspected that she had either moles or voles but wasn't sure. So she phoned a licensed wildlife control officer. He was certain she had voles, rather than moles, offering this easy means of remembering food preferences: The "V" in Vole stands for Vegetable. The "M" in Mole stands for Meat.

So, What Are Voles?
Voles tunnel near the surface and travel in mole tunnels as well. So people often confuse voles with moles, which are insectivores. Except for their short tails, voles also resemble mice and so are commonly called "meadow mice." Voles feed mainly on roots, stems, and seeds of herbaceous plants—and on tree bark, especially in winter.

Voles are good for the ecosystem. Besides aerating soil and improving its drainage, they are a crucial link in the food chain between carnivores and plants. Because voles feed around the clock, they are breakfast, lunch, dinner, and midnight snack for a great variety of predators, including snakes and birds of prey. At times, voles represent 85 percent of the barn owl's diet.

Domestic cats also prey on voles. But my friend and gardening mentor Kathy Nelson laments, "People who don't have a serious vole problem always tell me confidently, and often smugly, 'YOU need a cat.' But the worst vole problem I ever saw was on a property with 14 barn cats that got fed only on weekends."

Diet. Voles normally favor protein-rich foods. Although researchers know much about vole food preferences, there's little research on vole dislikes. We do know that, among herbaceous ornamentals, voles avoid well-known toxic plants, such as daffodils (Narcissus). Based on my research on plants toxic to deer, it seems logical that voles too would avoid monkshood (Aconitum), lady's mantle (Alchemilla), lily-of-the valley (Convallaria), corydalis (Corydalis), and bleeding heart (Dicentra). As to crop plants, there's little information on vole repellency.

Vole populations can fluctuate several times a year with no human intervention, or they can be full-scale cyclical irruptions every 4 5 years, suddenly skyrocketing to more than 200 voles per acre and then crashing on their own near zero. Regarding population irruptions and crashes, biologists debate relative importance of food supply, predation, snow cover, and territoriality as crash factors. More recently, biologists are considering cannibalism and toxic plants. That is, overcrowding and resulting food shortages could well increase fights among adults and cannibalism of nestlings. Overpopulation could also force dependence on less appealing food plants, whose roots are often more toxic than aboveground parts.

Vole Species. Of the 20 or so vole species north of Mexico, we have three in our region: The Meadow vole (Microtus pensylvanicus), the Woodland vole (Microtus pinetorum), and the Southern red-backed vole (Clethrionymys gapperi). As it turned out, Mary Ann had meadow voles.

Telltale Signs
Dying Plants. Many people mistakenly assume that a yellowing or drooping plant always indicates either disease or malnutrition. If a dying plant pulls out easily with most of its roots chewed off, that's voles!

Runways & Nests. A sure sign of meadow voles and red-backed voles (mainly surface traveling) is many tunnel-like, criss-crossing runways that are roofed-over by high grass and weeds. These runways become obvious as snow melts away. Meadow and red-backed voles often nest aboveground within mounds of grass. These nests are often under or against protective cover such as rocks, logs, and brush piles. By contrast, woodland voles (a.k.a. pine voles) remain mostly underground.

Chewed Tree Bark. Voles chew tree and shrub bark near the ground or at snow line, leaving tooth marks in tiny crosshatch patterns about 1/8-inch wide and 3/8-inch long. These tiny teeth marks can partially or completely girdle a tree, killing it. Although voles may damage roots and bark of trees and shrubs throughout the year, girdling damage is greatest during long winters. That stands to reason wherever soil is frozen, because frozen soil prevents voles from tunneling and dining on fleshier roots, which they prefer. And snow cover allows voles to travel unseen by most predators and subsist on what must seem to them meager, low-protein rations. There tends to be comparatively little damage where there's little to no snow cover.

Voles favor fruit trees and berry shrubs, yet woody plants of all types are vulnerable, especially when young bark is thin. Studies of vole damage to conifers vital to the lumber industry showed lowest vole damage to white spruce, which grows well in our region. In the same study, several larch species also proved of low appeal to voles. Coincidentally both spruces and larches are of low appeal to deer.

How to Deal with Voles?
Combined measures can significantly reduce vole populations without eliminating them. Options include: mowing and minimizing ground cover, especially during fall cleanup; selecting resistant plants; tilling before planting; using metal-mesh fencing; encouraging predators; using repellents; and using lethal traps. As for poisons, I strongly discourage use of poisons outdoors because they are inhumane and because they often poison nontarget species, including pets and children.

Minimizing Cover. My friend Kathy Nelson has maintained a thriving perennials nursery in western Connecticut, despite a relentless population of pine voles (aka woodland voles). This species is hard to trap because its stays mostly underground, unlike meadow voles. Kathy finds it helpful to conduct a thorough fall cleanup and shave her perennial beds down to an inch or two.

Resistant Plants. Regarding pine voles, Kathy says, "There are probably a few plants they won't eat. But the best you can say about a plant is that "it hasn't been eaten YET!" A few plants seem to contain some chemical that keeps them safe. In addition, Kathy has found that plants with a dense root system seem to have a better chance than plants with a loose, running root system. She's found that voles have little interest in a wide variety of ferns. As to perennials, in her most recent Fine Gardening article, Kathy mentioned these native plants (hardy in our region) as pine-vole resistant in her garden: Amsonia hubrichtii & A. tabernae-montana (Blue star); Asarum canadense (Canadian wild ginger); Chelone lyonii (Turtlehead); Eupatorium fistulosum (Boneset); Eupatorium fistulosum (Joe-Pye weed); Monarda didyma & cultivars (Bee balm); Phlox glaberrima (Smooth phlox); Pycnanthemum species (Mountain mint); Solidago species (Goldenrod); Waldsteinia fragarioirdes (Barren-ground strawberry). Yet Kathy feels confident in recommending only blue star amsonias, mountain mint, and goldenrods.

Cats & Other Predators. Although determined "mousers" can catch a goodly number of voles and other rodents, cats often get help from wild predators. Alas, unless we take precautions, our housecats also take a heavy toll on birds, especially near feeders.

Installing Fencing. Ironically, the fences we erect to keep rodents and deer away can also keep vole predators away. Regarding trees and shrubs, remove mulch and leaf litter from trunk bases. Cornell advises installing cylindrical 1/4-inch wire-mesh "tree guards" around the base 3 6 inches deep, if possible without damaging existing roots. Cylinders should be taller than anticipated snow cover.

To protect small garden areas, a mesh barrier only one foot aboveground or above anticipated snow cover can work because voles are poor or reluctant fence climbers. And because voles tend not to be deep tunnelers, the mesh needs to extend only 6 10 inches below ground. However, if you also hope to keep out woodchucks and raccoons, aboveground fencing needs to be about 4 feet tall and topped with either solar-powered electric wire or mechanical deterrents. For woodchucks and rabbits, simply bend a slightly buried portion of mesh outward 90 degrees about one foot, creating a concealed shelf that woodchucks have trouble figuring out. Metal mesh can also protect plants from voles inside cold frames. For this, fashion a mesh underground screen that fits just inside the base of the cold frame. Use stainless-steel staples to fasten the edges.

Using Repellents. Gardening writer Lorraine Ballato discourages voles and other rodents by scattering crushed oyster shells and hot red-pepper flakes onto soil over her bulbs and around perennial roots and annual plantings. On Lorraine's recommendation, mail-order garden supplier White Flower Farm tested oyster shells and pepper flakes over tulip bulbs with such success that it now sells 10-pound bags of oyster shells (whiteflowerfarm.com). Lorraine also likes the red-pepper flakes because they blend into the landscape, while being inexpensive, nontoxic, and available at most supermarkets and health-food stores.

Using Scare Devices. University research hasn't found ultrasonic devices or soil vibrators effective for voles.

Live Trapping. New York State discourages live-trapping of wildlife, also prohibiting the transport and release of wildlife beyond one's own property. This, for good justification: Released animals can transfer a host of parasites and diseases to other wildlife. Besides, live-trapped animals can die of stress inside traps or die soon after release because, in unfamiliar habitat, they are more vulnerable to the elements and to predators.

Lethal-Trapping. The goal should be to trap heavily all at once, rather than in steady small numbers. Heavy trapping drops the population quickly and slows the rate at which it can rise again.

Proof that this method works is provided by the same Mary Ann McGourty we met at the beginning of this article. On her consultant's advice, Mary Ann and her husband acquired about 30 snap traps of the type shown in the accompanying photo. The McGourtys baited each trap with peanut butter and placed each near a vole hole. They covered each trap and hole with a plastic one-gallon plant pot and weighed that down with a rock so birds and other critters wouldn't get hurt.

The McGourtys checked their traps each morning. By year's end, they had caught 290 voles. "The whole experience amazed me," Mary Ann says. "The next year, we didn't have a vole problem and so didn't continue trapping. But, without trapping over the next five years, our vole population became large again."

Old-style snap traps require two-handed setting and removal of rodents, which can expose bare fingers to vole parasites and diseases. Newer snap traps that open and close like spring clothespins allow one-hand operation. Thus, they can reduce chances that your fingers will contact the rodent, or its blood, fur, and feces. You can also avoid skin contact either by donning single-use latex or nitrile gloves or by grasping a thin plastic grocery bag so it serves like a protective mitten that allows you to "bag" the vole or other rodent for burial or for disposal in the trash. Also avoid breathing airborne fur or dust from vole urine or feces.

Unbaited snap traps (sometimes called professional traps) have large treadles. They will catch voles unbaited if placed in vole runways and wiggled into the soil a bit, so the treadle aligns with the soil surface. Traps are available at volume discount from wildlifecontrolsupplies.com. As to baits, voles find apples and peanut butter irresistible, but so do mice and larger rodents such as squirrels and chipmunks, as well as raccoons, opossums, and even passing bears.

Neil Soderstrom is the author of a forthcoming full-color book on outwitting garden mammals, soon to be titled and released by Rodale Books.