Shrews are mouselike animals, but they are not mice, and they do not have the chisel-like front teeth that characterize mice, beaver, and other rodents. Instead, they have sharp, spiky teeth, used for hunting prey instead of gnawing on plant material. Shrews are more closely related to moles than to any other Missouri mammals.
Shrews, like moles, are small mammals with an elongated head, often with a movable snout projecting well over the mouth; small to no external ears; very small eyes; teeth that are not well differentiated into incisors, canines, and premolars; 5 toes on each foot; and a primitive brain.
Members of the shrew family have the first or central incisors of both upper and lower jaws greatly enlarged and specialized into grasping pincers. The front and hind feet are about equal in size. Small external ears, or flaps, may be present. The eyes are tiny and probably provide very limited vision. The fur has a plushlike quality and will lie either forward or backward.
Six species of shrews occur in Missouri
Specialists use details of the skull and teeth to identify Missouri’s six species of shrews, but the following descriptions are useful for the rest of us:
1. The North American least shrew (Cryptotis parva), sometimes called simply the "least shrew" or the "bee shrew," is one of the smallest mammals in Missouri, measuring only about 3 inches from the tip of the nose to the tip of the tail. It has a long, pointed snout that extends considerably beyond the mouth and contains the nostrils at the end; tiny, black eyes; large ear openings hidden in the velvety fur; a distinct neck; moderately slender body; small front and hind limbs with 5 claw-bearing toes each; and an extremely short tail. The fur is soft and short and is not differentiated into underfur and overhair. The back is dark brown to brownish gray while the belly is gray. The upper surface of the tail is colored like the back and the undersurface like the belly.
The least shrew is distinguished from cinereus and southeastern shrews by the shorter tail and from short-tailed shrews by its smaller size, brown to brownish-gray color on the upperparts, and fewer number of teeth.
The least shrew has a large range in North America. They are generally abundant and probably occur statewide. Their preferred habitats include sites with open grass, brush, and dry, fallow fields, with marshy or timbered areas to a lesser extent.
2–4. Short-tailed shrews (genus Blarina) have an exceedingly pugnacious and energetic nature. For a long time, they were considered a single, widespread species (called the short-tailed shrew, B. brevicauda). Now, four species are recognized, with three occurring in Missouri. Specialists use cranial measurements and DNA sequencing to ID the different species.
- Northern short-tailed shrew (Blarina brevicauda)
- Southern short-tailed shrew (Blarina carolinensis)
- Elliot’s short-tailed shrew (Blarina hylophaga)
Because the three species look so similar, we treat them together here. All have a pointed head; distinct neck; cylindrical body; short, slender legs with 5 clawed toes on each foot; and a short, furred tail. The flexible, sensitive snout, which contains the nostrils, projects slightly over and beyond the mouth. The tiny black eyes are capable of light perception, but overall their vision is poor. The external ear opening is large but concealed in the fur. The senses of touch and hearing are well developed; that of smell is poorly developed. The velvety fur is short and brushes equally well in any direction. A microscopic examination shows whiplike tips on the hairs, similar to the hairs of moles but unlike those of any other mammal.
While short-tailed shrews are generally gray in color, they are darker on the back and lighter on the underparts, feet, undersurface of the tail, and around the mouth.
Short-tailed shrews are distinguished from the cinereus and southeastern shrews by their grayer color and shorter tails, and from the least shrew by their larger size and dark gray color on the upperparts. Specialists will note that short-tailed shrews have 32 teeth while least shrews have only 30 (sometimes 28) teeth.
Short-tailed shrews occur statewide, but each species’ range is imperfectly known. Their populations can fluctuate violently from year to year. They live in dark, damp, or wet localities in flooded areas or fields covered with heavy, weedy growth. They occur less often in grassy cover.
5. The cinereus shrew (or masked shrew) (Sorex cinereus) is distinguished from short-tailed and least shrews by a longer tail (the tail is more than one-half the length of head and body) and from the southeastern shrew by the grayish brown color on the upperparts and slightly longer tail with an obvious constriction at the base.
Usually scarce throughout its North American range, in some places and times it can be very abundant. In Missouri, it occurs in low, damp areas along streams and in floodplains (usually not in grasslands) in the northern half of the state. Our Missouri population seems to represent a southward range expansion from Iowa that occurred since the 1970s.
6. The southeastern shrew (Sorex longirostris) is distinguished from short-tailed and least shrews by a longer tail (the tail is more than one-half the length of head and body) and from the cinereus shrew by the reddish-brown color on the upperparts and a slightly shorter tail without an obvious constriction at the base.
Uncommon across Missouri, the southeastern shrew probably occurs in all but the northwest corner of the state. In most of its North American range, it is associated with marshy or swampy areas, or wooded places with dense ground cover. In Missouri, it is known mostly from dry upland sites with some woods.
Habitat and Conservation
The preferred habitats for each species are mentioned in the descriptions above, since they can be helpful for identification. In general, Missouri shrews run on the ground surface, amid leaf litter, and just under the ground.
Most of our species frequently use runways and tunnels originally built by moles and mice, as well as building their own tunnel systems. Short-tailed shrews may build tunnels extending to nearly 2 feet below the surface, but our other species’ burrows are shallower. Surface tunnels and runways may only be just beneath a layer of sod or within leaf litter.
Many shrews live under or deep within decaying logs or stumps, or under rocks. Their nests — where they raise their young, or where they overwinter — are often in chambers of their tunnel systems lined with grass and leaves. The cinereus shrew has specialized chambers for food storage, resting, and raising young.
Although shrews are famously belligerent to each other and usually live solitarily, the least shrew sometimes digs tunnels cooperatively (with more than one individual working on the project), and during winter, up to 31 least shrews have been recorded together in one nest, apparently sharing body heat.
Different shrew species have slightly different food preferences, but in general they focus on insects, including larval and dormant forms, plus earthworms, snails and slugs, spiders, centipedes, and other small animals. The short-tailed shrews, being slightly larger, may also eat larger prey, including salamanders, small snakes, birds, mice, and other shrews.
Our three species of short-tailed shrews have a powerful venom in their saliva that immobilizes insect prey and extends the time fresh food is available, so it facilitates food hoarding. Also, it slows the heart and breathing and may break down muscle tissue of larger victims.
Least shrews typically attack the joints of the jumping legs of crickets and grasshoppers, which helps subdue these insects.
Shrews typically do not eat much plant material. Short-tailed shrews, however, are more likely to do so than the other species, especially in winter, when they eat roots, nuts, fruits, berries, and fungi.
Because shrews do not hibernate, they must continue to eat during the winter. During this time, they seek out dormant insects such as overwintering larvae and pupae. Many of these are in the moth, butterfly, and beetle groups. Many of these grubs, caterpillars, and pupae overwinter in leaf litter, in the soil, in rotting logs, and other places where shrews live.
With their high metabolisms and active lives, shrews must eat a tremendous amount of food, relative to their size. The cinereus shrew may eat three times its own body weight every 24 hours. The least shrew can eat 75–100 percent of its own body weight a day, and the short-tailed shrews can eat 50 percent of their weight each day.
Because they feed principally on chitinous-bodied insects and other small invertebrates, shrews (like bats) have sharp-cusped molar teeth that cut up the hard parts of their prey. The incisors of shrews are modified into grasping pincers that are well suited for holding the hard bodies of the large, struggling insects the tiny shrew feeds upon.
For a long time, the shrews and moles used to be placed in a mammal order called Insectivora, which contained a variety of small insectivorous (insect-eating) mammals. But Insectivora has been divided into several new orders and is no longer an official grouping.
Today, most mammalogists agree that true shrews, moles, and solenodons, along with hedgehogs, gymnures, and desmans, belong in the same order. This new order is named Eulipotyphla. Molecular (DNA) evidence, which shows degrees of genetic relationships, prompted this reorganization.
Before order Eulipotyphla was proposed and accepted, true shrews, moles, and solenodons (but not the hedgehogs, gymnures, and desmans) were considered to be in order Soricomorpha. Slightly older references may still use this term.
Most of Missouri’s shrews generally breed from spring through fall, having several litters each year. Short-tailed shrews typically have only 1–3 litters a year and occasionally breed during winter, too. Shrews usually breed during their first year of life, often by the fall of their first year. Gestation varies by species, but is generally about 22 days.
Young, about the size of honeybees at birth, develop rapidly and are weaned in about month. Cinereus shrews are weaned after just 20 days. Least shrews are weaned in 3 weeks and look fully grown within a month. Southeastern shrews stay in the nest for 3–4 weeks until fully grown. In most species, the mothers provide all the parental care, but in least shrews, apparently both parents care for the young.
Shrews, especially when young, have a high mortality. Shrews in general do not live very long. They may die of shock, from accidents, and from cold. Short-tailed shrews usually live for only a year or 18 months, with most surviving for no more than one winter. Short-tailed shrews may potentially live for three years.
It is difficult to determine a shrew’s sex externally. On average, males are slightly larger and heavier than females. Males do not possess a scrotum; their testes are contained within the body during their whole lives. Females may be identified by teats in their groin region.
Shrews, like many other mammals, produce odors from glands that signal to others of their species their sex and receptivity for breeding. Their musky odors, rubbed in a tunnel, also signify ownership of a tunnel and help individuals establish a territory.
Shrews help make the outdoors an interesting place. Like bats, they have poor vision and use sonar to sense their surroundings. Like hummingbirds, they are tiny and busy, with fast metabolisms, and they are pugnacious with their own kind. Like moles, they have poor vision, have silky fur that can be petted in any direction, and spend a lot of time in underground tunnels.
Populations may decline precipitously in timbered areas that are cleared, and concentrations of pesticides could be a concern due to the predatory nature and high consumption rates of shrews.
Researchers have been studying chemical compounds in the venomous saliva of short-tailed shrews. These chemicals might be helpful in treating a variety of human diseases, ranging from high blood pressure and migraines to some types of cancer.
Many insect lawn and crop pests, such as certain beetle grubs and moth caterpillars including cutworms, are routine chow for shrews.
Mammalogists studying least shrews can have a difficult time surveying populations of that tiny, seldom-seen animal. One way they judge distribution and abundance of least shrews is by recovering parts of that species in the stomachs, droppings, or pellets of predators.
The title of Shakespeare’s play The Taming of the Shrew arose from “shrew” being used as an unflattering label for a scolding, nagging, harsh person (usually a woman). Many animal names have been used as insulting terms for people, such as gorilla, snake, shark, buzzard, pig, and weasel. When people imaginatively assign human characteristics to animals, it's called anthropomorphism. But when the opposite occurs, and people are described in terms of animal characteristics, it's called zoomorphism.
These numerous and widespread tiny mammals are extremely important and contribute in many ways to their environment:
- through their predatory nature, they help control insects and rodents;
- through their tunneling beneath the litter and debris of the forest floor, they aerate and mix the soil, helping rainwater to penetrate into the ground instead of running off the surface;
- through their own bodies, they furnish food for other animals and add to the organic content of the soil;
- some shrews aid in decomposition by feeding on dead animals.
Shrews are preyed upon by snakes, owls, hawks, shrikes, opossums, weasels, skunks, raccoons, foxes, bobcats, and domestic cats and dogs. The tiny least shrew may be preyed upon by the larger short-tailed shrews. Some animals may find certain shrews, especially the cinereus and short-tailed species, unpalatable because of their musky odor.
As with other mammals, a variety of mites, ticks, fleas, flukes, fly larvae, and other parasites vex shrews, contributing to their mortality.
Shrews, with their high metabolisms and continual need for food, are active nearly any time of day or night. As a general rule, they are almost constantly busy and rest only periodically. They tend to be most active above ground at night. They do not hibernate.
With their poor eyesight and dark environments, shrews use sound to its fullest advantage. They communicate with each other with a wide variety of sharp squeaks, twitters, clicks, teeth grinding, shrill chatters, and chirps. Also, they make ultrasonic sounds (so high-pitched that humans can’t hear), which they apparently use in navigating in tunnels and during dark conditions. Some researchers explain that shrews’ use of echolocation is different from bats’, because bats use their sonar to home in on moths and other targets, or avoid objects in a cave during flight, while shrews might use theirs for sensing the general size, textures, and other characteristics of a tunnel.