The Soricidae family encompasses over 385 known species of small mammals commonly known as shrews. These creatures are found across most of the world’s continents, inhabiting diverse environments from forests to grasslands. Despite their widespread presence, shrews are frequently mistaken for rodents, such as mice, due to their small size and general appearance. However, shrews belong to a distinct order of mammals, possessing characteristics that differentiate them from other small animals.
Defining Physical Characteristics
Shrews possess distinctive physical features, including an elongated, pointed snout. Their eyes are very small, and their tiny ears are covered by short, velvety fur.
Distinguishing shrews from rodents like mice involves examining several key anatomical differences. Shrews have five toes on each foot, a contrast to most mice which possess four toes on their front feet. Shrews also have sharp, spike-like teeth that wear down over their lifetime, unlike the chisel-like, ever-growing incisors characteristic of rodents.
Shrews also differ significantly from moles in their physical build. While both have pointed snouts and dark fur, shrews are more slender and lack the enlarged, paddle-like front feet moles use for extensive digging. Moles’ eyes and ears are often not visible, while a shrew’s eyes, though small, are discernible.
Most shrews are tiny, with many species no larger than a mouse. The Etruscan shrew, for instance, is among the smallest known living terrestrial mammals, measuring about 3.5 centimeters (1.375 inches) long and weighing around 1.8 grams. In contrast, the Asian house shrew, one of the largest species, can reach about 15 centimeters (6 inches) in length and weigh approximately 100 grams.
Unique Biological Traits
Shrews have a high metabolic rate, requiring them to consume food constantly to avoid starvation. Their hearts can beat rapidly, ranging from 800 to 1500 times per minute, depending on the species. This rapid metabolism is partly attributed to their small body size, which results in a large surface area-to-volume ratio and consequently, rapid heat loss.
To sustain their energy demands, shrews must eat a substantial amount, consuming between half and three times their own body weight in food daily. If deprived of food for even a few hours, many shrews can starve. This constant need for sustenance drives their persistent foraging behavior.
Certain shrew species, such as the northern short-tailed shrew, possess venom, making them one of the few venomous mammals. Their saliva contains toxins, which they use to paralyze or subdue prey. The venom is delivered into the victim through grooves in their lower incisors, rather than hollow fangs. This potent venom allows shrews to immobilize prey, sometimes larger than themselves, and even store live, paralyzed victims for later consumption.
Some shrew species also demonstrate a basic form of echolocation. Similar to bats and toothed whales, these shrews emit series of ultrasonic squeaks or clicks. They use the returning echoes for close-range spatial orientation, helping them navigate their environment and locate food in dark or cluttered spaces.
Global Habitat and Diet
Shrews are broadly distributed across the globe, inhabiting nearly every continent. They are absent from native populations in New Guinea, Australia, New Zealand, and most of South America, though a naturalized population exists in the northern Andes. This wide distribution reflects their adaptability to various environments.
These mammals occupy a diverse range of habitats. They can be found in forests, grasslands, marshes, and even tundra regions. Some specialized species are adapted to specific niches, such as climbing trees, living underground in burrows, dwelling under snow, or hunting in aquatic environments like streams and ponds.
Shrews are insectivorous, meaning their diet consists of insects. They hunt for a variety of invertebrates. Common prey items include:
Beetles
Grasshoppers
Butterfly and moth larvae
Spiders
Worms
Snails
Slugs
Centipedes
Millipedes
Larger shrew species may expand their diet to include small vertebrates, such as frogs, salamanders, snakes, mice, and even small birds or other shrews. While insects form the bulk of their intake, some species also consume seeds, nuts, and other plant matter, demonstrating dietary flexibility.
Ecological Significance
Shrews play a role within their ecosystems as predators of invertebrates. By consuming large quantities of insects, worms, and other small creatures, they contribute to the natural regulation of these populations. This predation helps maintain ecological balance in various habitats.
Beyond their role as predators, shrews also serve as a food source for other animals. They are preyed upon by various predators, including owls, hawks, and snakes. Larger mammals such as foxes and weasels also hunt shrews.
Many mammalian predators kill shrews but refuse to eat them. This behavior is attributed to the musky odor shrews emit from scent glands on their flanks, which makes them unpalatable. Despite this deterrent, shrews remain a link in many food webs.
The conservation status of the Soricidae family varies greatly among its many species. While numerous shrew species are common and classified as “Least Concern,” some face threats due to habitat loss and environmental changes. The decline of certain shrew populations can impact the broader food web, affecting both the invertebrate populations they control and the predators that rely on them as a food source.