Shrews
Shrews are small, insectivorous mammals belonging to the family Soricidae, with the Etruscan shrew being among the smallest known mammals, measuring less than 1.5 inches and weighing just 0.07 ounces. Their diverse family is found across all major land masses except for polar regions and a few isolated areas, predominantly in Africa. Shrews have a body shape reminiscent of moles, featuring long, mobile snouts, tiny ears, and short, thick fur, and they require a high food intake, needing to eat every two to three hours to survive. These creatures possess venomous saliva, which helps them immobilize prey and defend against predators; however, their unpleasant odor and taste deter many would-be attackers, making them less susceptible to predation.
Shrews typically live solitary lives, marking territories and mating throughout the year, except in colder climates where mating seasons are more defined. Females can have up to ten litters a year, with young becoming independent after just a few weeks. While generally harmless to humans, some shrew bites can be painful. Shrews play an important ecological role by controlling insect populations and consuming carrion, thereby contributing to a balanced environment. However, habitat loss and competition from introduced species have put some shrew species at risk.
Shrews
Shrew Facts
Classification:
- Kingdom: Animalia
- Subkingdom: Bilateria
- Phylum: Chordata
- Subphylum: Vertebrata
- Class: Mammalia
- Order: Soricomorpha or Eulipotyphla (formerly Insectivora)
- Family: Soricidae, with over twenty genera and more than three hundred species
- Geographical location: Worldwide except for poles, Australia, New Zealand, and Greenland
- Habitat: Most in gardens, fields, marshes, and woodlands; some are semiaquatic and spend much time in freshwater
- Gestational period: Thirteen to twenty-four days
- Life span: One to five years in the wild
- Special anatomy: Mobile snout, venomous saliva, glands that make offensive excretions to dissuade predators
Shrews are usually very small; the Etruscan shrew (or Savi’s pygmy shrew) is probably the smallest known mammal on earth, less than 1.5 inches long and weighing 0.07 ounces. The shrew family, Soricidae, was the largest family of the former order Insectivora, which was a catch-all grouping for small, insect-eating mammals until it was shown to be polyphyletic and divided into various other orders. Soricidae was included in the order Soricomorpha, which was then combined in some taxonomic systems with the order Erinaceidae to form the monophyletic order Eulipotyphla. True shrews of the Soricidae family are taxonomically different from otter shrews, elephant shrews, treeshrews, and West Indies shrews, which are named for their superficial similarities.
Shrews inhabit all major land masses except polar regions, Australia, New Zealand, and Greenland, with the most species found in Africa. They are one of the most diverse families of all mammals in terms of number of species. Shrews are useful to gardeners because they are insectivores, eating many pest species. They also inhabit fields, marshes, and woodlands. Some shrews are semiaquatic.
Shrews are often mistaken for mice because of their small size and vaguely similar bodies. Their habits and bodies are actually more like those of moles, to which they are more closely related than to rodents. Shrews have long, mobile snouts, tiny ears and eyes, and bodies covered with short, thick hair colored gray, brown, or black. Smaller shrews are under two inches long, while the largest—the Asian house shrew—can be one foot long. They eat insects, worms, small fish, and plants, depending on the species. Weasels, foxes and owls eat shrews. However, the shrew’s unpleasant odor and taste protects it from excessive predation.
Physical Characteristics of Shrews
Shrews have sharp teeth and are both vicious and ferocious. When attacked or disturbed, they fight wildly. They live alone, stake out territories, and hold them against invaders. As added protection, some shrews have venomous saliva, which they use to poison prey. Unlike snakes, which deliver venom with fangs, shrews deliver their venom through special teeth grooves. Shrews also have whiskers that aid detection of prey at night. Shrews live in gardens, forests, woodlands, and grasslands. Most dig burrows, though some species do not burrow and others are semiaquatic. Some are able to tunnel under snow, and they do not hibernate, though species in areas with cold winters may undergo seasonal changes in appearance and behavior.
Shrews forage day and night and must eat every two to three hours to survive. This great need for food leads shrews to eat anything available. Depending on habitat and species, they eat insects, worms, carrion, seeds, nuts, plants, shellfish, frogs, and fish. Shrews hear and smell well. This helps them find prey and avoid predators. Some creatures kill shrews, but most will not eat them because they smell and taste bad. The smell and taste is due to secretions from skin glands most plentiful at knee and elbow.
The Life Cycles of Shrews
Shrews live alone except when mating. This occurs year round, except in cold climates, where mating is from March to September. Gestation, two to three weeks, takes places in nests that females dig. A female can have ten litters a year. Each litter contains three to ten furless, blind young. Offspring are full grown four weeks after birth.
Because of long mating seasons, some mothers nurse a litter while pregnant. Young leave nests after two to three weeks. Females mature in 1.5 months and males in 3 months. Courtship is short since shrews fight, even with mates. The life spans of shrews range from one to five years, depending on species.
The American Short-Tailed Shrew
The American short-tailed shrew inhabits southeastern Canada, the northeastern United States, Texas, and Louisiana. They have thick, gray-black fur, are four to five inches long, have one-inch tails, and weigh one ounce. Like other shrews, American short-tailed shrews constantly seek food, eating insects, earthworms, snails, small vertebrates, centipedes, spiders, mice, frogs, and plants. They have venomous saliva, used to stun and kill prey, which is also painful to humans and large animal predators. Predators of the shrews are owls and other raptors.
American short-tailed shrews live alone except when mating, which happens from late winter to the next September. Courtship is short because shrews are harsh, even to mates. Females give birth after two to three weeks to litters of four to nine young. Young leave after a month. As with other shrew species, males are mature in 1.5 months, females in three. The life span of these shrews is two to three years.
Most shrews are harmless to humans, though bites of some species cause severe pain. They are useful in gardens and farms, where their consumption of insects and grubs cuts down harmful insect populations. Shrews are also useful ecologically because they eat carrion, preventing its decay and resultant endangerment of humans and other animals. Some species of shrews are threatened or endangered, generally due to habitat loss or predation and competition by introduced species. Humans often kill shrews, mistaking them for mice or rats.
Principal Terms
carrion: dead, decomposing animal bodies
gestation: the time developing mammalian offspring are in the uterus
venom: a poison made by an animal
Bibliography
Bailey, Jill. Discovering Shrews, Moles, and Voles. New York: Bookwright Press, 1989.
Churchfield, Sara. The Natural History of Shrews. Ithaca, N.Y.: Comstock Publishing Associates, 1990.
Ciszek, Deborah, and Phil Myers. "Soricidae: Shrews." Animal Diversity Web, U of Michigan Museum of Zoology, 2014, http://animaldiversity.org/accounts/Soricidae/. Accessed 6 Oct. 2016.
Crowcroft, Peter. The Life of the Shrew. London: M. Reinhardt, 1957.
Ferraro, Dennis. "Shrew." Nebraska Extension: Acreage Insights, U of Nebraska-Lincoln, 2016, http://acreage.unl.edu/Shrew. Accessed 6 Oct. 2016.
Merritt, Joseph F., Gordon L. Kirkland, Jr., and Robert K. Rose. Advances in the Biology of Shrews. Pittsburgh: Carnegie Museum of Natural History, 1994.