Meet Your Neighbors

Shrews: 24/7 Carnivores

Math quiz: You weigh 100 pounds and eat like a shrew. How many quarter-pounders do you need to eat every day to survive? (Hint: A shrew can eat 1.5 times its weight every day.)

Though rarely seen, shrews are leading wild, frenzied lives beneath our feet. Among the most primitive of mammals, they benefit ecosystems and, in turn, humans. At first glance, a shrew might look like a mouse, but shrews have a wedge-shaped skull, a pointed nose, and ears hidden by dense, dark fur.

The shrew you’ll most likely encounter in the Chicago region is the northern short-tailed, Blarina brevicauda. A few are likely scurrying in your back yard right now. In fact, says Illinois Natural History Survey Senior Mammalogist Joseph Merritt, the short-tailed shrew, not the mouse, is the most abundant small mammal in Illinois. This shrew measures four inches long, has a one-inch tail, and weighs a mere ounce.

Three other shrews live in the region. The masked shrew is nearly as abundant as the short-tailed but often selects wetter areas. The less abundant least shrew often selects grassy areas. And the pygmy shrew, the rarest in Illinois, is one of the smallest mammals in the world, weighing little more than a dime.

A shrew creates its own tunnels, but the opportunistic mammal also uses tunnels created by voles.

Shrews remain active almost 24/7, scurrying about when you are at work,  at home, and asleep. Talk about a fast-paced lifestyle! There’s no hibernation in the winter for these critters, either — just two hours without food may mean death. Fierce predators, shrews eat insects (especially beetles), earthworms, snails, and occasionally even a mouse.

Having poor hearing and eyesight, shrews hunt by smell and touch. Some shrews, including the short-tailed, paralyze the victim with poisonous saliva, and cache food for a midnight snack.

Shrews must burrow deeper underground in winter. “In winter, shrews have an abundant food source under the ground,” says Merritt, namely dormant beetle adults and larvae. Like humans, they often gain weight. Males in most shrew species mark their burrows with glandular secretions. In the world of shrews, it’s every man for himself. If one male meets another, both freeze. They then squeak loudly at a pitch nearly inaudible to humans, stand on their hind legs for a moment, and finally chase each other, often biting and kicking.

The northern short-tailed shrew typically has two or three litters a year, with five to eight young in each. This shrew hides its nest of grass, leaves, and hair beneath a log or in a burrow. At birth, the young are as tiny as honey bees, and need at least 22 days of mother’s milk before they can be on their own.

Shrews are an important component of the food web. Merritt refers to Paul Ehrlich’s analogy: “Small mammals are like rivets in an airplane. Eliminate a couple rivets and you’ll be OK, but a couple more and eventually you have problems, and the wings eventually fall off.” With their tremendous appetites, shrews control insect numbers in grasslands, forests, and back yards. They also become prey for minks, hawks, owls, and snakes.

Though shrews are abundant, they’re not that easy to see. Merritt suggests looking on the ground beneath a bird feeder for two-inch-wide holes. That, he says, is where the northern short-tailed shrew likely stuck its nose out to snatch some fallen seeds. Also look for shallow tunnels leading to a small hole.

Quiz Answer: If you were a shrew weighing 100 pounds, you would have to eat 600 quarter-pounders a day to survive.

— Sheryl De Vore

Joseph Merritt’s book, The Biology of Small Mammals, will be published by The Johns Hopkins University Press in fall 2008.