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Volume 38 Issue 9 • June 26-July 2, 2008
now in our 38th season

Life Underground:
Moles, Voles, and Shrews

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

Here at the Field Station, and all over the island, you’ll find acres of mole tunnels, softening the ground and providing yet another way to trip for those of us who are clumsy.  Nantucket has very few mammals, but we do have several species that spend a great deal of their time living a fossorial or underground life, such as moles, voles, and shrews.

Voles are members of the order Muridae (rodents) which includes mice, rats, voles, and lemmings. The most common specimen found on Nantucket is the meadow vole (Microtus pennsylvanicus). The vole of Muskeget Island, Nantucket County, is considered by some scientists to be a subspecies of Microtus pennsylvanicus, although other researchers list it as a separate species, Microtus breweri, which is also known as the Muskeget vole or beach vole. Subspecies and species offshoots occur when there is genetic isolation which is a natural result of mammals living on islands separated by water.  The beach vole is larger, more grizzled, and pale brown when compared to its darker, slightly smaller cousin. Perhaps due to less predators, the Muskeget beach vole is a better parent and less aggressive than Microtus pennsylvanicus. Female beach voles produce a slightly smaller litter than meadow voles (3.5 offspring vesus 4.0 on average). According to Don E. Wilson’s 2003 book The Smithsonian Book of North American Mammals, the beach vole is indeed a separate species as established by a statistical analysis of skull and tooth characteristics and that is good enough for me. The typical diet of a Muskeget beach vole is beach grass.

Voles can live either above or below ground and they dig snow tunnels in the winter, which is called subnivean behavior. Voles eat various plants such as grasses and sedges, and they will quickly recolonize a newly opened field. The meadow vole has a long, cylindrical, fur-covered body with chunky build and a short tail. It has a rounded nose and ears that are partially buried in its black or brown fur. Their fore and hind paws differ in that the front paws have four toes whereas their hind paws have five. On average, they are six to seven inches in length, including a 1.3-2.5 inch tail and they weigh from 0.7 – 2.3 ounces.

The meadow vole is active year-round, usually at night. It also digs underground burrows where it stores food for the winter and females give birth to their young. Although these animals tend to live close together, they are aggressive towards one other. This is particularly evident in males during the breeding season. The meadow vole is sometimes called a field mouse or a meadow mouse. The vole has a very short lifespan in the wild, often less than a year. Its main predators on Nantucket are raptors, snakes, and feral cats. Many voles are snatched up by hawks and owls, particularly barn owls. In fact, the welfare of barn owls, short-eared owls and northern harriers is literally tied to the presence or absence, ups and downs of this species. Meadow voles are considered one of the most prolific species in the world.

Shrews are members of the family Soricidae in the Order Insectivora (insect eaters). Insectivores are the descendants of the most primitive placental mammals and are the predecessors of all other placental mammals.  Earliest known fossils date back 130 million years ago.  These insect-eating mammals have long-pointed, flexible snouts with a finely developed sense of feel (some are carnivorous). Their sight and hearing are poorly developed, and they all have musk glands, like the weasel family.  They have five clawed toes on all four feet, in contrast to rodents, like mice, that have only four toes on their forefeet.   These very small, non-hibernating mammals have high metabolic rates and may consume up to twice their body weight per day. Most insectivores are ferocious predators with an insatiable appetite, with a constant need to forage. Shrews have a very short life span and high reproductive rate. Shrews have poorly developed eyesight, but have a well-developed sense of smell, which they use in hunt of prey.  Their small size enables them to access food sources unavailable to most mammals or birds. 

Shrews are fairly vocal, with many sounds made that are above the hearing range of humans.  Like whales and bats, water shrews, wandering shrews and masked shrews utilize high frequency ultrasonic sounds for hunting, orientation, protection, and communication. Shrews are very aggressive and usually solitary, only meeting to mate. They are very nervous; known to die from fright from loud noises, even from thunder.  Normally, our local shrews will feed on prey found in its burrows.  They have a very diverse diet, preferring earthworms, but also consuming insects, centipedes, millipedes, spiders, slugs, snails, mice, frogs, salamanders, minnow, crayfish, roots, berries and nuts, and even other shrews (seems somewhat greedy).  Sometimes half of the shrew’s diet may consist of meadow voles.  In fact, research indicates that meadow vole and northern short-tailed shrew populations may fluctuate together in cycles. 

While moles are disdained by some land owners, their benefits are numerous. They consume larvae and adults of many pest insects, such as Japanese beetles. In addition, their tunneling activity loosens the soil, aerating it and mixing deeper soils with surface material, all of which improve soil quality.  Moles are also members of the mammalian order Insectivora. Predators of moles include snakes, skunks, foxes, weasels, coyotes, hawks and owls. On Nantucket, moles have only snake and avian predators to worry about, along with perhaps domestic dogs and feral cats.

Moles are larger than shrews, usually with proportionally shorter tails.  They have enlarged forefeet, reduced hind feet and pelvis, and short thick fur that can be rubbed backward or forward, which helps it wriggle through tunnels. The eyes are poorly developed, to the point that they can only detect light from dark. Hearing is excellent, and the sense of smell is well-developed.  Moles are active both day and night and don’t hibernate or aestivate, but will spend up to ten hours a day sleeping. Like shrews, they have a voracious appetite, feeding primarily on earthworms and other invertebrates.  The extremely sensitive snout of the mole is unmatched in the animal kingdom.  It is covered with a dense array of nervous receptors connected to nerve cells supported by a rich supply of blood vessels.  These are organized into structures called Eimer’s organs, most outrageously developed in the star-nosed mole.  In addition, the snout, paws, tail and back of the head have sensitive bristles, like cat whiskers, that aid the mole in detecting objects. It is interesting that moles is that they have twice as much blood and hemoglobin as other mammals of similar size. This allows moles to breathe more easily in underground environments with low oxygen.

Moles are "fossorial" mammals; they spend practically all their lives underground. They make two types of tunnels. The pushed-up type we see are temporary feeding tubes, normally used for only a few weeks. Most food is obtained by prey falling into the feeding tunnels, rather than excavating tunnels to find the source.   Tunnels will follow the grubs and worms (shallow in summer, deeper in winter). The second, deeper ones (down to three feet) are more permanent. These are used for sleeping, escaping from most predators and avoiding the cold of winter.  Nesting and resting chambers may be attached to these deep tunnels.  Where food supplies are favorable, generations of moles may inhabit the same tunnels. Moles will occasionally make vertical shafts to the surface to disperse excavated soil, especially in heavier, clay soil, often spreading out the soil to conceal the tunnel. In ideal soils, moles can tunnel at a rate of over 1 and ½ feet per minute. Moles often consume an amount of food equal to 60 to 100% of their body weight daily. To satisfy this demand, a mole will dig up to 150 feet of new tunnels a day.

Moles differ from shrews in several characteristics.  Moles have white teeth; not brown-tipped.  Moles have enormously enlarged, long-clawed forefeet.  The smelling ability of moles is more limited than shrews. Star-nosed moles can be gregarious, sharing tunnels and paths with other moles (the least shrew - and the northern short-tailed to a lesser extent - is the only shrew known to be sociable).  Because of the protection afforded by the fossorial habit, only one annual litter of two to six offspring occur.  Finally, moles have molt lines, appearing as a sharp line of demarcation between old and new pelage.

From the 17th through the 19th centuries, moleskins were used for caps, purses, tobacco pouches, and trimmings for garments.  American imported as many as 4 million moleskins a year from England.  The demand for moleskins was so great that its extinction in Germany was anticipated.  In 1959, approximately one million skins were still trapped in Britain.  Most moleskins now come from Russia. Our large populations of moles on Nantucket are mainly due to the abundance of grub species and earthworms.

Although I like moles, I am also not trying to keep either a garden or a lawn mole-free. Some advocate using pesticides to kill the grubs upon which the moles feed. These products kill all soil insects, including those that are beneficial, so use of these pesticides is not very effective. Moreover, since the moles will not know that the lawn has been treated with the pesticide they may still make forays into the lawn in search of food. Last. But not least, moles really like to eat earthworms, which are not usually affected by these pesticides. The Massachusetts Audubon Society web site lists three ways to reduce mole populations in your lawn:

1) Don’t over water your lawn! Over watering can keep earthworms and other mole prey near the surface and result in increased surface tunneling. Encourage native plant species to establish themselves in the lawn. Native grasses do not usually require as frequent watering as non-native species.

2) Erect barriers around small flower or garden beds by burying quarter-inch mesh hardware cloth 12 inches deep, with a 12-inch extension at a 90-degree angle. This fencing should extend 5 inches above ground.

3). Repellents: Castor bean or castor-oil plant (Ricinus comunis) and a species of spurge (Euphorbia latharis) are often recommended as mole repellents. To treat a given area, sprinkle a castor oil mixture on the ground. Castor oil mixture directions: Whip 2 ounces of castor oil with 1 ounce of liquid dish detergent in a blender until it holds its shape. Add 6 tablespoons of water and whip again. Fill a sprinkling can with water, add two tablespoons of the castor mixture and sprinkle on areas of heaviest concentration of burrowing. This works best after a heavy rain or watering. NOTE: many wildlife management sites do not agree that any repellent works, including castor oil.

Most wildlife management sites say that there is no scientific proof that sonic devices, vibrating devices, moth balls, human hair, or any other home remedies work. Moles tend to move their feeding tunnels around as temperature and moisture changes occur in search of different food items, which may appear to a home owner as if they were succeeding in a mole war. Only trapping is considered to be an effective treatment to remove moles and it is illegal to use the majority of mole traps and/or repatriate moles (or other underground mammals) in Massachusetts.

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