Are Shrews Dangerous?

Last updated: 28th September 2023

The shrew is a tiny animal that looks similar to a small mouse. With their small size, generally between 3-5 inches in length, they do not look dangerous. Shrews are venomous, however, and contain enough venom to subdue 200 mice.

Shrews can be lethal to other small animals due to their sharp teeth and venom. Shrews primarily use their sharp teeth and toxic saliva to subdue and consume insects, worms, and other small invertebrates. Their saliva contains enzymes and toxins that aid in the breakdown of prey items, but these toxins are not typically harmful to humans.

Although small, these creatures can pack a punch. There are over 387 species of shrews worldwide, but only three live in North America. Not all shrews are venomous. In this article, we look at whether shrews are dangerous. 

Are Shrews Venomous Or Poisonous?

Shrews are considered venomous rather than poisonous because they actively deliver their toxins through specialized adaptations, such as grooves in their teeth and venom glands in their mouths, to immobilize and subdue their prey or defend themselves. This active delivery method is characteristic of venomous animals. When a shrew bites its prey, it introduces venom through the grooves in its teeth, which can induce paralysis in the victim.

In contrast, a poisonous organism or substance relies on passive contact or ingestion to deliver toxins. For example, a poisonous plant might contain toxic chemicals that can harm animals that eat it, but the plant does not actively inject or deliver toxins.

Unlike most mammals, some species of shrew are venomous. Shrews have grooves in their teeth that allow saliva, which contains toxic compounds, to flow into their prey’s wounds. This toxic saliva aids in immobilizing and digesting their prey. The venom is potent against small animals including mammals, insects, and other invertebrates. The American short-tailed shrew’s venom is sufficient to kill two hundred mice. 

The gland in the mouth releases venom when biting another animal. The venom does not immediately kill but will paralyze the animal. If it’s an intruder to its territory, the shrew will leave it to die, but if it is prey, the shrew will eat the paralyzed animal. Shrews can kill animals as large as mice, birds, frogs, salamanders, and other shrews using their venom.  

Are Shrews Dangerous To Us? 

Shrews produce venom, but the amount of venom is not dangerous to us. A shrew will have no intention to attack a human. Shrews will generally run away and avoid any conflict with a human. However, if a shrew is cornered, it may bite to get a chance to escape.

There are very few cases of shrews attacking human beings. The venom may be extremely dangerous to small animals, but not to us. 

While shrew venom is not life-threatening, a bite from a shrew can result in extreme pain and swelling to the affected location. The pain and swelling will go away after a few days. However, as with all animal bites, the best advice is to seek medical attention immediately.

Shrews are wild animals that often carry bacteria and can also carry rabies. To avoid any further complications, get the wound treated by a doctor.

What Do Shrews Eat?

Shrews are primarily insectivores, which means they primarily feed on insects and other small invertebrates. Their diet can include:

1. Insects: Shrews commonly consume various insects such as beetles, ants, spiders, and caterpillars.
2. Earthworms: Shrews are known to feed on earthworms, often hunting for them in the soil.
3. Small Invertebrates: They may also eat other small invertebrates like centipedes, millipedes, and snails.
4. Amphibians and Reptiles: In some cases, shrews may consume small amphibians and reptiles, including frogs and lizards.
5. Small Vertebrates: While less common, larger shrew species have been known to prey on small vertebrates like mice, voles, and birds.
6. Plant Matter: Although their primary diet consists of animal matter, shrews may occasionally consume plant material such as seeds or fruits.

Shrews have a high metabolism and need to eat frequently to sustain their energy levels. They are active hunters and use their keen sense of smell to locate prey. Their diet can vary depending on their habitat and the availability of food sources in their environment.

How To Recognize A Shrew?

Recognizing a shrew can be a bit challenging due to their small size and relatively inconspicuous appearance. However, there are some key characteristics that can help you identify a shrew:

1. Size: Shrews are tiny mammals, typically measuring only 3 to 5 inches (7.5 to 13 centimeters) in length, not including their short tail. They are among the smallest mammals.
2. Body Shape: Shrews have a slender, cylindrical body with short legs and a short tail. They have a pointed snout.
3. Fur: Shrews usually have dense fur that can vary in color, including gray, brown, or reddish-brown. The fur may have a slightly darker color on their backs and a lighter color on their undersides.
4. Ears and Eyes: Shrews have small, hidden ears and tiny, bead-like eyes. Their vision is typically poor, but they have an acute sense of smell.
5. Teeth: Shrews have sharp, pointed teeth, and their upper incisors have grooves through which venom flows when they bite.
6. Behavior: Shrews are active, fast-moving creatures, often seen scurrying on the ground or through vegetation. They have a high metabolic rate and need to eat frequently.
7. Vocalization: Shrews can emit high-pitched squeaks and chirps, especially when distressed or communicating with other shrews.
8. Habitat: Shrews are commonly found in a variety of habitats, including woodlands, grasslands, gardens, and wetlands. They prefer areas with plenty of cover and hiding spots.
9. Diet: Shrews are insectivores and primarily feed on insects, earthworms, and other small invertebrates. Their diet may also include small vertebrates.
10. Activity: Shrews are most active during the night (nocturnal) and may also be active during dawn and dusk (crepuscular).

Remember that shrews are small and often go unnoticed due to their size and nocturnal habits. If you come across a small, mouse-sized mammal with the above characteristics, it could very well be a shrew.

Want to know more about shrews? Here are 75 facts you may not know.

Are Shrews Dangerous To Pets? 

Shrews are fierce predators and release venom when hunting or defending. The venom from a shrew is not lethal to large animals like cats and dogs. However, a bite can get infected, and the venom can be painful. If you believe a shrew has bitten your pet, please take them to see a vet as soon as possible.

Cats and dogs may attack shrews. There are even instances where they have eaten shrews. Shrews are not considered a danger to pets because of their small size and the amount of venom they produce.

They may attack small animals or those slightly larger than themselves. However, it is unlikely that most dogs and cats are at risk.

Are Shrews Aggressive? 

Shrews exhibit territorial behavior, often displaying high levels of aggression towards other shrews and potential intruders. It’s worth noting that they are not aggressive towards humans, primarily due to their diminutive size.

Shrews make their homes in diverse locations such as forests, swampy areas, gardens, fields, and woodlands. Once they identify a suitable nesting site, they defend their territory tenaciously, occasionally even resorting to life-or-death battles.

To demarcate their territories, shrews employ a potent scent secreted from their bodies. However, their most formidable weapon against intruders and potential predators is their sharp teeth and venom.

In North America, shrews come in various sizes, with the Northern short-tailed (Blarina brevicauda) shrew claiming the title of the largest species. In contrast, the least shrew (Cryptotis parva) ranks as the smallest shrew species in North America, measuring around 3 inches in length. They all share common features, including a long, pointed snout and a distinctive tail.

Among shrews, the Northern short-tailed shrew stands out as the most widespread and common species in the United States, flourishing in nearly all regions of the country, particularly along the East Coast.

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References And Further Reading

Shrews (Life of the Past) by Robert J. Baker, James L. Patton, and George F. Feldhamer

This book offers a detailed look at shrews, their evolutionary history, ecology, and physiology. It is part of the “Life of the Past” series.

Shrews, Mice, and Rats (Roger Tory Peterson Field Guides of the World) by Charles A. Reed

A field guide that helps you identify and understand shrews, mice, and rats from around the world, including North America.