Untamed Shrews: Life at High Speed
At rest, the average human heart beats 60 times each minute and goes unnoticed by all but the most attentive. But if, after exercise or a good scare, your heartbeat jumps to 120 beats per minute, the throbbing grabs your attention. Now, imagine, if you can, a heart-bursting rate of 1200 beats per minute, 20 each second, and you have entered the high-speed world of a shrew, one of earth’s most frenetic animals. At a shrew’s pace, 60 times faster than our own, we’d be bundles of boundless energy, zooming rapidly from place to place. We’d be hungry all the time, needing constant fuel to maintain such a blistering metabolism. And we’d die more quickly, for an animal’s average heart rate is related to lifespan: the higher the rate, the shorter the life. Instead of a 70-year lifespan, we’d live but a year in a state of wild abandon. We would be untamed shrews.
Shrews do, indeed, live life at a rapid pace. They run everywhere. Something moving as slowly as a human must seem as if it were bound in molasses. From the shrew’s perspective of time, our movements might seem like the advance of glaciers or the return of spring. Because they are very small and have a high metabolism, shrews eat enormous quantities of food. Those kept in captivity eat 3 times their own body weight every day and will starve to death if deprived of food overnight.
Shrews, like moles, are insectivores, and the two are closely related. They eat primarily insects, earthworms, and snails. Their metabolism is so high that they would starve if restricted only to voluminous but nutrient-low vegetation. While they may occasionally eat oily seeds or nuts, they are carnivores, not vegetarians. Their teeth reveal this dietary preference and are sharp, pointed, and numerous. Their saliva is poisonous and is used to kill their prey. When they bite the prey, saliva on their teeth enters the wound and paralyzes it. Although moles may dig up your lawn, they do not eat flower bulbs. Instead, rodents such as mice or meadow voles do the damage. Rodents have large incisors with which they constantly gnaw at vegetation and seeds. Unlike the carnivorous shrews and moles with sharp, pointed teeth, rodents are mostly herbivores.
Shrews are also closely related to the insectivorous bats. Not only are their diets similar, but both groups use echolocation to find their prey. Shrews tunnel under leaf litter in dark runways. Instead of relying on eyesight in these dark tunnels, they use hearing to detect the reflections of their high-pitched squeaks that bounce back from objects in front of them. Bats, which are active at night, also rely on hearing and echolocation rather than eyesight. In both, the eyes are relatively small.
The most commonly encountered shrew in this area is the Northern Short-tailed Shrew. They are rarely seen unless found dead on top of the ground or captured by cats. Their tails are only 1/3 the length of their body, whereas in most other shrew species the tail is more than half the length of the body. Their short, dense fur is gray to black and they are relatively large for a shrew at 5 ½ inches, including the tail.
The related moles have very large front feet adapted for digging, and their eyes are permanently closed by flaps of skin. They, too, are rarely seen, but their humped-up tunnels are conspicuous in lawns. The family dog or cat may catch one for you from this underground burrow system. If you find one dead, you’ve lost one of the many insectivores that keep those pesky insects under control. They are especially effective against the grubs of beetles such as Japanese beetles, exotic pests that are hard to manage.
Northern Short-Tailed Shrew; Comparison of Northern Short-Tailed Shrew and Eastern Mole
Copyright 2002 by Jennifer E. Frick
Text and photos may not be used without permission of the author