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Northwest Wildlife Online
by John M. Regan
Order Insectivora: Moles and Shrews
Bats Bears Canines Felines Mustelidae (Weasels) Rodents Pinnipeds Cetacea Insectivores (Moles and Shrews) Hoofed Animals
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This page is dedicated to Patrick H. Thompson of West Linn, Oregon, a man who probably knew more about insectivores in general and moles in particular than anyone in North America. Mr. Thompson certainly knew more about the subject than anyone I spoke to. I am indebted to him for his book, "Of Moles and Men: The Battle for the Turf," for providing fascinating insights to the habits and lives of these amazing animals of the subterranean world. Mr. Thompson's book taught me more than any other source I found on the subject. Mr. Thompson was a true scientist and lover of all things of nature. Our wildlife world is poorer for his passing.
Two examples of the most ancient and fascinating terrestrial mammals in North America. On the left is the Shrew Mole (Neurotrichus gibbsi). Moles live out their lives in dark tunnels under the earth, coming to the surface, much to the annoyance of lawn connoisseurs, only occasionally. Shrews, like the Common Shrew (Sorex cinereus) on the left, are the smallest mammals in North America. Although seen as rarely as moles, shrews are not soil burrowers; they prefer leaf litter and dense undergrowth. Despite their tiny size, both of these insectivores are active and voracious predators.
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Two Families and 16 Species of Instectivora represent wildlife in the Northwest:
Family Talpidae - The Moles
Shrew Mole - Neurotrichus gibbsi
Coast Mole - Scapanus orarius
Townsend's Mole - Scapanus townsendi
Broad-footed Mole - Scapanus latimus
Family Soricidae - The Shrews:
Common/Masked Shrew - Sorex cinereus
Preble's Shrew - Sorex preblei
Vagrant Shrew - Sorex vagrans
Montane Shrew - Sorex monticolus
Fog Shrew - Sorex sonomae
Baird's Shrew - Sorex bairdii
Pacific Shrew - Sorex pacificus
Water Shrew - Sorex palustris
Marsh Shrew - Sorex bendirii
Merriam's Shrew - Sorex trowbridgii
Trowbridge's Shrew - Sorex merriami
Pygmy Shrew - Sorex hoyi
(formerly known as Microsorex hoyi)
If I had to pick the single most fascinating group of terrestrial animals in the Northwest, or anywhere else, I'd point to the Insectivores. These secretive, furious little bundles of energy live brief unseen lives characterized by insatiable appetites, frenetic energy, and a feisty courage all out of proportion to their size. The smallest mammals in our country and in the world insectivores define the diminutive boundary at which an animal can maintain warm bloodedness.
Among the first mammals to appear on the planet the insectivores have an ancient heritage, scurrying around even before the placental animals. The brain is small and most literature I've read describes it as "not highly evolved" or words to that effect.
Why the fast pace of life? Body volume is the main reason. The larger a mammal is, the more it must work to shed excess heat. Smaller mammals, with a relatively large surface area compared to body volume must work hard to retain heat. At the size of shrews and moles (especially shrews) the atmosphere is robbing their body of heat nearly as fast as they can produce it. Hence some shrews consume nearly their entire body every twenty four hours and can easily starve to death in less time than that.
And they are small. The Pygmy Shrew, about one inch long and 1/4 of an ounce, is generally credited as the smallest mammal in North America. At the other end of the Insectivore scale stands the 6 ounce Townsend's mole, a giant by comparison. Size reduction, however, does not confer an ability for longevity. Two to three years is about max, with some species having a lifespan of just 18 months.
Although referred to as insectivores, these little guys tackle and eat a wide variety of insects, worms, and anything else small enough for them to go after. In a hunting technique similar to bats, shrews may even use echolocation to locate prey. Moles can actually detect the vibrations of an earthworm digging through the soil.
Moles
Moles, as every gardener knows, are adapted for a life below the earth (fossorial). The forearms are composed of powerful muscles that drive wide, tough forefeet ideal for digging. The snout and tail are extremely sensitive for detection of odor and vibration. Eyes are nearly non-existent there are no external ears. Mole fur, unlike most mammals, does not lay in a particular pattern and easily folds in whatever underground direction the mole happens to be going in. to compensate for the low oxygen - high carbon dioxide levels of their underground life, moles have oversized lungs and blood with a great capacity to hold and carry oxygen.
Although each species of mole has a preference for a particular soil type, there are a couple of characteristics they all agree on: they must be able to dig through the soil and the soil must contain the right food. Disturbed soil, whether in a plowed farmers field or a beautiful new lawn is ideal mole country. It is easier to tunnel through and filled with the earthworms and various other invertebrates they love.
Moles can sense the slightest vibration of intended prey; an exceptionally important ability for an animal that inhabits a world of darkness. Mole tails are covered with sensory hairs. When these tails are held against the side of the mole tunnel they pick up vibrations as slight as the movement of an earthworm. Now that's sensitive! But these guys do eat vegetation in addition to the invertebrates that make up so much of their diet.
Shrews
The vast majority of insectivores are shrews. Even from the list of species in the Northwest it is obvious that these creature outnumber their mole cousins; about 70% of known insectivores are shrews. Like moles, shrews are found throughout the world, although shrews possess an even greater range. They range in size from the startlingly large African Otter Shrew (over one foot) to the tiny Pigmy Shrew.
Shrews generally spend life above ground. As a result they are not nearly as dependent upon soil types as the moles and can inhabit desert environs. One very interesting species, the Northern Water Shrew, is especially adapted for swimming. Hair on the hind feet give it a flipper quality and these shrews move surprisingly rapidly on the surface and under water. The first time I saw a water shrew I thought I was seeing things. Had I just seen a mouse swimming underwater? I quickly realized what I had seen and I considered myself privileged. Unfortunately we do not have waters shrews in our area. I'd love to see one of these little guys again.
Shrews and moles are tough to observe without special equipment. Moles can sometimes be surprised under a board or log in an area near their characteristic mole hills, but quickly disappear, and get pretty cranky if attempt to pick one up. Shrews require much more attention to little movement in grass or leaf litter and a nose to the ground approach. Even then the glimpse is apt to be brief. But building the special equipment is not terribly difficult. A couple of large panes of Plexiglas bolted together and filled with dirt provides a fascinating glimpse into their lives. Should you attempt this, however, please keep in mind the extraordinary appetites of insectivores. They can easily starve to death in a single day so it is best to let them go after quickly completing your observations.
Bats Bears Canines Felines Mustelidae (Weasels) Rodents Pinnipeds Cetacea Insectivores (Moles and Shrews) Hoofed Animals
Opossums Raccoon Family Rabbit Family Skunks
Birds Mammals Reptiles Amphibians Fish Invertebrates Home
Mission Editor Bio Contact Wildlife Park Links Further Study Wild Employment Northwest Trek
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