Oh To Be So Shrew-d

The most abundant mammal in Illinois and a frequent visitors to fields, forests and backyards is an animal that is almost never seen.   Among the most primitive of animals, the Northern short-tailed shrew, Blarina brevicauda, is an insectivore, eating mainly insects.  The shrew family contains 312 species worldwide of which 33 are native to North America.  They are small mammals with short, dense fur, five-clawed toes and small eyes and ears.  A wedge shaped skull ends in a long, pointed nose.  An adult shrew is four inches in length plus a one inch tail and weighs about one ounce.

The shrew is a secretive animal, staying hidden when above ground.  They live mainly underground, digging tunnels or using old tunnels abandoned by voles.  Their burrow entrances are marked by a glandular secretion that serves as a warning to keep other shrews away.  A male and female usually mate for life, but meetings between other individuals most often result in combat.  They are fierce competitors and will initially try to chase each other away. Combat is marked by much screeching with kicking and biting until one relents.  Fights end when one combatant assumes a submissive position, laying on its back, and the other leaves.  Rarely do fights end in death.

Breeding begins in early spring.  Shrews can have two to three litters each year with five to ten young born in each litter.  Nests are built from grass, leaves and hair and are located under logs or inside burrows.  At birth, a young shrew is blind, pink, and hairless.  Babies are the size of a honeybee.  A baby shrew feeds on mother’s milk for about three weeks until it is able to fend for itself.  A typical lifespan is one to two years. 

Shrews can eat one-and-a-half times their weight each day.  They eat several times every 24 hours and are active at all times of the day and night.  They take short rest periods between meals, but no long sleep period.  Shrews have poor hearing and eyesight and find their prey by smell and touch.  Long runways are constructed underground, attracting beetle larvae, earthworms, snails and an occasional mouse.  Unique among mammals, the Northern short-tailed shrew can paralyze a victim with venom contained in its saliva, and then save the prey for a later meal.  They can deliver a painful bite to humans, but the venom will not harm us.  Shrews live deep underground in winter, continuing to feed on dormant beetle adults and larvae throughout the season.

Three other shrews also live in Illinois but are much less abundant.  These include the masked shrew, Sorex cinereus, found in wetland areas; the least shrew, Cryptotis parva, active at night in grassy fields; and the pygmy shrew, Sorex hoyi, found in deep woods.  The pygmy shrew is thought to be very rare, but that may be because of its secretive nature and diminutive size, weighing about 1/16th of an ounce.

The shrew may be a difficult animal to observe, but it is an important link in the food chain.  They maintain a healthy control on the insect populations where they live.  In turn, they provide food for minks, hawks, owls and snakes.  They are abundant and secretive, but if you want to observe their behaviors, one of the best places to start is to look under bird feeders in your backyard.  Search for a small, two inch diameter hole where the shrew may be poking out its nose in search of falling seeds for a snack.