Mice and Voles

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Reviled, Revered, Roasted

Of all the multitudinous mammals on the planet, rodents comprise not only the largest number of species –some 2,000 worldwide –but in terms of sheer biomass, mice and voles greatly outweigh the many predators that feed on them. They live in almost every type of habitat, from mountain slopes to the depths of coal mines, inside cold-storage meat lockers and in the hottest tropic clime. Most feed at night and are active year-round; only the jumping mice hibernate. In North America, mice and voles comprise 82 of the 125 native mouse/rat species. 

All are prolific breeders on a mind-boggling scale. Reports of great “mouse plagues” throughout history make for some decidedly squeamish reading. In 1917, a house mouse plague in Australia destroyed millions of tons of stored and field crops until an extermination campaign managed to reduce their numbers –temporarily- by the tens of millions. Thousands of tons of mouse carcasses (at sixty thousand mice per ton) were eventually gathered up, with one town alone killing six million mice in a single night. In 1968 in Monterey County, California, some 14 million mice were exterminated in two months during a field mouse plague that so infested the soil that it writhed, as if the mice were tilling it themselves to find food. 

But the sheer invasive weight of their numbers and the food they eat and ruin is only part of the reason we react to mice with such queasy dismay. Unlike their larger, more feared rat cousins, mice and voles can hide and thrive in the smallest corners of our dwellings, and they carry all the same disease vectors that rats do (the notorious “black death” of bubonic plague, tularemia, salmonella, the spectacularly lethal Hantavirus), plus a few more, including botulism, trichinosis, leptospiral jaundice (a wasting disease of the human liver transmitted in mouse urine), and the bacterium for Lyme disease, spread by ticks and currently the most common insect bite ailment in the United States and Europe. The Puulmala [sic] virus, a member of the Hanta genus found in Scandinavia, causes sudden severe bleeding of the capillaries until critical organs fail, almost always before the victim’s immune system can defend itself. It is carried by voles. 

And yet even in the face of such pestilent havoc, mice and voles have their place in the ecology, our corner of it included. They consume large numbers of weed seeds and insects along with garden-ravaging slugs and snails. The grasshopper mouse of western America is a fierce hunter, consuming one-half its body weight every day in its namesake insects (which form plagues of their own) plus legions of beetles, lizards, and even its own relative, the pocket mouse. When kept as pets, grasshopper mice are often let loose at night to rid homes of cockroaches and scorpions.

In Costa Rica, a climbing arboreal species of mouse pollinates a type of air plant that grows only in the tops of trees. The nimble mouse runs through the branches, sticking its snout into the plant’s bell-shaped flowers, one after the other, searching for nectar. An odd side benefit of field mouse plagues in 17th century Holland was the discovery that deeply-gnawed hyacinth bulbs responded to their wounds by producing innumerable bulblets that grew into new bulbs. Thus began the practice of slashing bulb hearts to increase the supply of marketable hyacinths.  

Mice provide food for other animals, including birds of prey, wolves, foxes, weasels, snakes, even for a few spiders such as the black widow –and people. Since most of us today did not grow up eating the squirrels and woodchucks that were once common to family dinner tables, we might imagine that humans dined on such creatures only in distant, desperate times of siege or famine. The fact is that mice, as well as rats, porcupines, beavers, and other members of the order rodentia, have all been considered gourmet fare at one time or another in every culture. This should come as no surprise to anyone versed in the history of human food preferences, which at one time or another have embraced such delights as broiled sheep eyes, stewed vulture intestines, dirt, flies in honey sauce, all kinds of insects, and various roasted versions of our currently favorite companion animals.

Stuffed baked dormouse is an ancient recipe still considered a delicacy in parts of modern Europe. In South America, field mice are skinned, skewered, and roasted over open fires. The famed Canadian writer Farley Mowat began eating the mice that invaded his Arctic field tent after he observed wolves preying on the same victual (and not decimating the caribou herds as the wolves had been accused of doing). Mowat flour-dipped and fried his mouse munchies with a methyl alcohol marinate and clove-flavored cream sauce. On the other hand, American novelist Upton Sinclair became a lifelong vegetarian after discovering in his early twentieth-century investigations of meat packing plants that rats were often sold to the unsuspecting public as beefsteak.

Rendered mice also appear in home remedies past and present. No less than the august first-century naturalist Pliny the Elder declared that dormouse ashes mixed with honey would alleviate earaches, goiter, epilepsy, and cataracts, and that “sodden mice” fed to toddlers would stop bed-wetting. This last charming bit of homey antidote appears again in a 19th-century Pennsylvania Dutch cookbook that recommends mouse pie not only for the curse of bed-wetting, but to cure measles and whooping cough. In our own time, mouse milk has been tested as an aphrodisiac, though its enormous expense, at $10,000 a quart in laboratories that use it in experiments, has kept it off the nightly drug commercial blitz, at least for now.

Furthermore, we seem to despise and revere the mouse in equal measure. In story, song and fable, mice are presented as heroic, wise, and true. In early Greek plays the mouse is a symbol of tenderness and sensuality. Aesop’s Fables deem mice as not only wise, but clever: they bell the cat, save the lion and reap its favors, serve as the essence of moral rectitude. During the Middle Ages it was believed that at the moment of death, the human soul departed for Heaven in the guise of a mouse. Though mice (along with rats and cats) were often hated and feared as agents of the devil, they also represented the virtue of meekness, humility, the smallest of the small. And in 20th century America we rooted for Jerry of “Tom and Jerry” cartoon fame; called on Mighty Mouse to fly in and save us; and are forever charmed by Mickey, the mightiest mouse of all, who not only became a famous international icon but made his creator Walt Disney one of the richest men of his time.

Still and all, there is the underlying, inarguable truth about mice and voles: When we find them in our kitchen cupboards, we want them out. Dead or alive. Preferably dead.  And fast.

In upstate New York, these are the types of small rodents we are most likely to see:

The House Mouse

Direct ancestor of all so-called “fancy” and white lab mice, Mus musculus is an Old World species inadvertently brought to North America (along with the brown rat) by European settlers in their shipping cargo. Six to eight inches long, in various shades of gray, the house mouse has a 3-inch, nearly hairless tail. It inhabits dwellings everywhere, in cities and in rural areas, squeezing through the tiniest of holes to get inside, where the food is. The house mouse feeds at night and is active all year long. It is agile and quick, though a hereditary middle-ear deficiency disturbs its sense of balance so it can’t move in a straight line –except when it walks backwards.

House mice (as well as deer mice) can run up almost any rough vertical surface and jump a foot high. They will eat just about anything, from grains and seeds to paper, glue, soap, and chalk. Electrical wires damaged by their chewing are fire hazards. In six months, one pair of house mice can eat four pounds of food and deposit about 18,000 fecal droppings. A female house mouse can produce five to eight litters a year with an average of half a dozen young each time. Much damage is caused by female mice as they chew various materials –paper, clothing, cardboard, insulation –to construct their nests. Six weeks later, the babies are old enough to reproduce, and can do so in complete darkness or in temperatures well below freezing. Meanwhile, the mother mouse can become pregnant two days after giving birth. If it were not for the relatively high mortality rate inflicted upon mouse numbers by various means, in six months this one female and her offspring could produce more than 2,500 new mice.

Each house mouse can live up to six years. Fortunately, it hardly ever does.

If you care to look closely, Mus musculus can be easily identified by the lack of grooves in its incisors. Plus, their feet stink, a byproduct of the unique “mousy” smell in their urine that is used in territorial scent-marking.

Deer and White-Footed Mice

Actually a pair of handsome little mice, Peromyscus maniculatus, the American woodland deer mouse, and its close relative Peromyscus leucopus, the white-footed mouse, have in recent years acquired notoriety for their roles in the rise and spread of Hantavirus and the now near-ubiquitous Lyme disease. Deer mice are small and white-bellied with long tails and large dark eyes suited for night vision. They are found in virtually every North American habitat, can swim if necessary and run at nearly five miles an hour for short distances. As do white-footed mice, deer mice consume cultivated grain, corn, berries, nuts and seeds, and moreover provide a service by eating grasshoppers and caterpillars, including those of the gypsy moth.

Neither mouse digs burrows of their own, but uses runways made by other small mammals. In winter, deer mice nest and travel underneath the snow cover in hollow logs, root channels, and rocks, living on stored food caches. Sometimes deer mice will winter over in bird houses or abandoned squirrel and bird nests up to 50 feet above ground. The white-foot (which looks much like a deer mouse except for its shorter tail) makes its home in just about any crevice anywhere, including human dwellings. It eats the same basic diet as the deer mouse, but will also prey on centipedes, snails, small birds, and other mice.

The first recognized outbreak of Lyme disease occurred in 1975 around the town of Old Lyme, Connecticut, where clusters of childhood arthritis attracted medical attention. It took several years of research to pin down the culprit as the bacterium Borrelia burgdorferi , which resides harmlessly in white-footed mice, themselves the feeding site of choice for larvae and nymphs of the deer tick. The baby ticks ingest the infected mouse blood, jump to their preferred deer hosts, and from there infest the surrounding vegetation and the humans who brush up against it. Currently, it is estimated that about half of all adult deer ticks in the northeastern United States carry Lyme bacteria.

Fortunately, only 1 to 3 percent of people bitten by the deer tick come down with Lyme, which is treatable with antibiotics if detected early enough. The same can’t be said for Hantavirus, which is carried by mice, rats, and voles and transmitted to us through air contaminated with their feces, urine, or saliva. In 1993 in the Four Corners region of the American southwest, a type of Hantavirus killed thirty-two otherwise healthy young adults who all suffocated when their lungs filled with plasma from damaged pulmonary blood vessels. It took epidemiologists months to discover the cause. By the end of 2001, Hanta had struck nearly 300 people in thirty-one states. With a fatality rate of 38 percent, it is among the most lethal viruses ever found in the United States. There is no specific treatment or cure.

The virus lives harmlessly in deer mice. A few years after the 1993 outbreak, a case of Hanta was identified in Brooklyn. Labeled the New York-1 variant, it is linked to the white-footed mouse. 

Traditional Navajo medicine has for centuries recommended the burning of any clothes soiled by mice, a wise move wherever one lives.

Voles

Sometimes referred to as the meadow mouse or field mouse, voles are the fat, short-tailed rodents you sometimes see dashing across roadways in broad daylight. Of the 26 species of voles in North America, the meadow vole is the most common. Stocky, with a blunt head and small, beady eyes, voles are the most prodigious breeders of their order, not to mention one of the fastest tunnelers alive. Voles have been clocked digging at 15 inches per minute! They are active day and night year-round, are good swimmers, and can cause a lot of damage to crops and trees in a very short time.

One of the first signs that voles live in your yard are the intricate runways that appear in mulch or underneath melting snow. Missing bark around the base of fruit and ornamental trees is another vole indicator. Feces and clipped vegetation, including seed, tubers, bulbs, and the remains of root crops, may be found in the runways. Voles can kill small trees by girdling them, with most of this damage occurring in fall and winter. No plant seems beyond their destructive capability. High vole populations will decimate field crops while their extensive tunnels and pathways wreak havoc on irrigation systems. Even Pacific Northwest bamboo, that mighty grass with stems strong enough to be made into flooring, is vulnerable to vole gnawing as it is to little else.

Voles have short life spans, two to sixteen months at most. But in that time, a female vole can produce as many as 17 litters a year. In ten months, a single pair of laboratory meadow voles and its offspring of three generations produced 2,557 young. Fortunately voles will eat each other, as well as other small rodents, and they provide sustenance to many other denizens of the wild. In fact, the fate of barn owls, short-eared owls, and northern harriers depends on the local population of meadow voles and their kin.

Sources

More Cunning Than Man: A Complete History of the Rat and its Role in Human Civilization Robert Hendrickson, Kensington Books 1983 (spec., chapters on the history of the mouse).

Every Creeping Thing: True Tales of Faintly Repulsive Wildlife Richard Conniff, Henry Holt and Company, 1998.

Peterson’s Field Guide to Mammals of North America, Fourth edition, 2006.

A Field Guide to Germs, Wayne Biddle, Anchor Books, revised and updated edition, 2002.

“Wildlife Notes: Mice and Voles,” by Chuck Fergis, Pennsylvania State Game Commission State Wildlife Management Agency, web site www.pennsylvanisgamecommission.org

Yardener’s Advisor Newsletter, “Voles/Diagnose Vole Damage,” www.yardener.com

University of Connecticut Integrated Pest Management web site, “Identification and Control of Mice and Voles,” by Norma Gauthier, Cooperative Extension Entomolgist, www.ucipm.com

“Hardy Bamboo Information,” BooShoot Garden leaflet, Seattle, WA, February 8, 2007.