Shrew

Shrew Facts

Size	1.4-5.9 inches (36 mm to 15 cm)
Speed	Unknown
Weight	0.05 to 3.5 ounces (15 mg to 100 grams)
Lifespan	1-2 years
Food	Insects, larvae, snails, invertebrates
Predators	Owls, weasels, foxes, snakes
Distribution	Europe, Asia, Africa, North America, Central America
Habitat	Dense and humid forests, grassland
Order	Eulipotyphla
Family	Soricidae
Scientific name	Sorex
Characteristics	Insectivore with a trunk-like snout; can shrink organs

Main Characteristics

Shrews are the smallest mammals in the world. Despite their appearance and name, they aren't actually mice, nor are they rodents. They belong to the family of insectivores. Shrews can be quite aggressive, and some species are even venomous. Their most distinctive features include a long, pointed snout and tiny eyes.

Lesser White-Toothed Shrew Lesser White-Toothed Shrew - Photo: Martin Pelanek/Shutterstock

Species

There are more than 350 species of shrews, including bicolored shrews, greater white-toothed shrews, lesser white-toothed shrews, water shrews, Eurasian shrews, African mole shrews, and Mexican shrews. The shrew resembles a mouse, but it is not a mouse and is not closely related to one either. It belongs to the insectivorous family, just like moles and hedgehogs.

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Distribution and Habitat

Shrews are found across Europe, Asia, Africa, North America, Central America, and Russia. They're absent only in Australia, New Guinea, and New Zealand. Most species thrive in moist forest environments, but there are also species that live underground, such as Asian mole shrews and African mole shrews. Additionally, some species are specially adapted to aquatic habitats, such as the water shrews.

Way of Life

Shrews are solitary creatures. Whether they're active during the day or at night depends on the specific species. Due to their small size and fast metabolism, they need to eat constantly and can only survive for a few hours without food.

Shrew Characteristics Shrew Characteristics - Photo: Rudmer Zwerver/Shutterstock

Appearance and Anatomy

Size and Weight

The Etruscan shrew is considered the smallest mammal in the world. Its body measures only 1.4-1.8 inches (35-48 mm) in length, with a tail that ranges from 9.4-11.4 inches (24-29 mm). It weighs a mere 0.05-0.09 ounces (15-26 mg). In contrast, the largest shrew is the Asian house shrew, which can grow to be 3.9-5.9 inches (10-15 cm) long and weigh between 0.8-5.1 ounces (23-147 grams). On average, these animals measure about 2.3-3.9 inches (6-10 cm) in length.

Eyes

The eyes of the shrew are quite tiny - smaller even than the head of a pin.

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Snout

Shrews have a long, pointed, snout-like nose that is very flexible, allowing it to bend in all directions. This feature is particularly useful for locating prey.

Fur

Shrews can be brown, gray, or black. Water shrews have a uniquely oily fur that traps air bubbles while swimming and diving, providing buoyancy. Their fur acts almost like a life jacket.

Teeth

Unlike rodents, whose teeth grow continuously, shrews have teeth designed to last a lifetime.

Shrew vs. Vole – What's the Difference?

Shrews and voles can easily be confused with one another. However, once you know what features to look for, distinguishing them becomes quite simple. Voles have a much shorter and broader nose, but they possess larger eyes and ears. It's also important to remember that voles are rodents, primarily feeding on grains, nuts, and seeds. In contrast, shrews mainly consume insects and other invertebrates. By the way, voles aren't venomous, but some species of shrews are.

Shrew vs. Vole – What's the Difference? Shrew vs. Vole – What's the Difference? - Photo: Jannis Bonner (left), David (right)/stock.adobe.com

Diet

Shrews are carnivores. They primarily enjoy a diet of insects, beetles, larvae, earthworms, spiders, millipedes, and snails. They also hunt for mice, scorpions, snakes, and frogs. Each day, they consume about half to three times their body weight. Occasionally, small fish, frogs, and caterpillars make it onto their menu.

Behavior

Defense

Shrews, due to their small size, struggle to defend themselves against predators. However, they have a clever trick to deter attackers: they emit a very unpleasant, skunk-like odor. Even humans can detect this smell.

Constant Eating

Shrews are among the few animals that need to eat constantly. They're on the hunt for food day and night and can only survive for a few hours without nourishment.

Hunting

Using Their Senses

Shrews require a constant food supply due to their rapid heartbeat and high energy needs. To locate their prey, they rely on their sense of smell, hearing, and whiskers.

Using Venom

Some types of shrews, like the water shrew and the American short-tailed shrew, have venom. When they bite, the venom flows through grooves in their teeth into the wound of their prey. This venom doesn’t kill the animals. Instead, it just makes them unable to move. The shrews then take their prey back to their burrows and store them. This way, they always have a supply of live food.

Eurasian Pygmy Shrew Eurasian Pygmy Shrew - Photo: Rudmer Zwerver/Shutterstock

Senses and Abilities

Senses

Shrews have poor eyesight because their eyes are quite small. However, they don’t really need good vision, as their most important senses are hearing, smell, and touch.

Swimming

Water shrews are exceptional swimmers. They are quite nimble and maneuver underwater with great skill.

Diving

Shrews can dive up to 6.5 feet (2 meters) deep. Considering their small size, that's quite an impressive feat! For shrews, 6.5 feet (2 meters) is equivalent to 65 feet (20 meters) for a human. To stay submerged, they have to keep paddling; otherwise, they shoot up to the surface due to the buoyancy from the air trapped in their fur.

Climbing

Shrew-mice aren't great climbers. They primarily inhabit the ground.

Echolocation

Bats aren't the only creatures that master echolocation. Shrews also use it to navigate their environment. However, when it comes to hunting, they primarily rely on their sense of smell and their sensitive whiskers.

Heartbeat

In humans, the heart beats around 50-100 times per minute, while in shrews, it can reach an astonishing 800-1,000 beats. The Etruscan shrew takes it to another level with up to 1,511 heartbeats per minute, which is even more frequent than a hummingbird in flight! Shrews essentially experience constant rapid heart rates, and it's not uncommon for them to die from a heart attack due to sudden fright.

Winter

Loosing Body Weight

The shrew doesn't hibernate. It stays awake all the time. However, it finds very little food in the snow. So how does it survive? To conserve energy, it shrinks in size. The smaller and lighter its body is, the less energy and food it requires. During the winter, it can lose up to half of its body weight.

Shrinking the Organs

To conserve energy, shrews actually reduce the size of their organs during winter. Their heart and lungs shrink, and their brain can decrease by 20-30%.

Shrinking the Bones

As for their bones, shrews can also make them smaller. In winter, their skull can be 15% reduced in size.

What Happens in Spring?

Once the exhausting winter has passed, shrews eagerly return to hunting, helping their bodies, organs, and bones to grow again.

Common Shrew Common Shrew - Photo: Sandra Standbrige/Shutterstock

Are Shrews Dangerous?

Venomous Bites

Water shrews and American short-tailed shrews have venom glands in their mouths. The amount of venom they contain could potentially kill 200 mice. This raises the question: Is a shrew's bite dangerous to humans? Fortunately, it’s not enough to pose a serious threat to us. While the bite can swell and be painful, caution is advised for those with allergic reactions. In such cases, it's best to consult a doctor.

Borna-Virus Transmission

Shrews have the ability to transmit the Borna virus, which can lead to encephalitis in humans, although such cases are quite rare. It's still wise to avoid contact with these animals.

Intruder in House and Garden

Shrews may wander into your garden or even your home, where they can leave behind urine and droppings. These can potentially carry bacteria and viruses, so it's important to keep an eye out for any signs of droppings both indoors and outdoors.

Life Expectancy

Shrews typically live for about 1-2 years.

Enemies and Threats

Natural Enemies

Their main enemies include owls, weasels, foxes, and snakes.

Human Impact

The biggest threat to shrews is environmental pollution. They're highly sensitive to toxins found in water and soil.

Importance for the Ecosystem

Shrews are considered beneficial creatures and a blessing for gardeners. Always on the lookout for food, they feast on unwanted pests like grubs and snails. This helps keep flower beds and vegetable gardens free from harmful insects.

Reproduction

Shrews are quite prolific when it comes to reproduction. They can have offspring around 10 times a year. After mating, it takes about 3-4 weeks for 4-10 babies to be born. Most species are capable of having their own young after just 2-3 months.

The Shrew Is Related To:

Mole
Solenodon

Animals in the Same Biome:

Sources:

„Etruscan shrew muscle: the consequences of being small“ (https://journals.biologists.com)
„Suncus murinus“ (https://www.sciencedirect.com)
„Largest brain-to-body-mass ratio in mammals“ (https://www.guinnessworldrecords.com)
„Fastest heartbeat in a mammal“ (https://www.guinnessworldrecords.com)
„Smallest aquatic mammal“ (https://www.guinnessworldrecords.com)
„Seasonal reversible size changes in the braincase and mass of common shrews are flexibly modified by environmental conditions“ (https://www.nature.com)
„Dive Performance and Aquatic Thermoregulation of the World’s Smallest Mammalian Diver, the American Water Shrew (Sorex palustris)“ (https://www.journals.uchicago.edu)
„One Health in action: Investigation of the first detected local cluster of fatal borna disease virus 1 (BoDV-1) encephalitis, Germany 2022“ (https://www.sciencedirect.com)