SHREWS

Shrews are small, superficially mouse-like mammals. Although their external appearance is generally that of a mouse with a long nose, the shrews are not rodents and not closely related. Shrews have feet with five clawed toes, unlike rodents, which have four. Shrews are also not to be confused with tree shrews, which are also unrelated.

Identification
The shrew is a small, mouse-sized mammal with an elongated snout, a dense fur of uniform color, small eyes, and five clawed toes on each foot. Its skull, compared to that of rodents, is long, narrow, and lacks the zygomatic arch on the lateral side characteristic of rodents. The teeth are small, sharp, and commonly dark-tipped. Pigmentation on the tips of the teeth is caused by deposition of iron in the outer enamel. This deposition may increase the teeth’s resistance to wear, an obvious advantage for permanent teeth that do not continue to grow in response to wear. The house shrew (Suncus murinus) lacks the pigmented teeth. Shrew feces are often corkscrew-shaped, and some shrews (for example, the desert shrew [Notiosorex crawfordi]) use regular defecation stations. Albino shrews occur occasionally. Shrews are similar to mice except that mice have four toes on their front feet, larger eyes, bicolored fur, and lack an elongated snout. Moles also are similar to shrews, but are usually larger and have enlarged front feet. Both shrews and moles are insectivores, whereas mice are rodents.

Worldwide, over 250 species of shrews are recognized, with over 30 species recognized in the United States, the US Territories, and Canada. Specific identification of shrews may be difficult. Taxonomists are still refining the phylogenetic relationships between populations of shrews. Consult a regional reference book on mammals, or seek assistance from a qualified mammalogist.

Range
Shrews are broadly distributed throughout the world and North America. For specific range information, refer to one of the many references available on mammal distribution for your region.

Habitat
Shrews vary widely in habitat preferences throughout North America. Shrews exist in practically all terrestrial habitats, from montane or boreal regions to arid areas. The northern water shrew (Sorex palustris) prefers marshy or semi-aquatic areas. Regional reference books will help identify specific habitats. A word of caution is in order, however. Distribution studies based on the results of snap-trapping research have a pronounced tendency to understate the abundance of shrews. Studies using pit traps are more successful in assessing the presence or absence of shrews in a particular location.

Food Habits
Shrews are in the taxonomic order Insectivora. As the name implies, insects make up a large portion of the typical shrew diet. Food habit studies have revealed that shrews eat beetles, grasshoppers, butterfly and moth larvae, ichneumonid wasps, crickets, spiders, snails, earthworms, slugs, centipedes, and millipedes. Shrews also eat small birds, mice, small snakes, and even other shrews when the opportunity presents itself. Seeds, roots, and other vegetable matter are also eaten by some species of shrews.

General Biology, Reproduction, and Behavior
Shrews are among the world’s smallest mammals. The pigmy shrew (Sorex hoyi) is the smallest North American mammal. It can weigh as little as 0.1 ounce (2 g). Because of their small size, shrews have a proportionally high surface-to-volume ratio and lose body heat rapidly. Thus, to maintain a constant body temperature, they have a high metabolic rate and need to consume food as often as every 3 to 4 hours. Some shrews will consume three times their body weight in food over a 24-hour period.

Shrews usually do not live longer than 1 to 2 years, but they have 1 to 3 litters per year with 2 to 10 young per litter. Specific demographic features vary with the species. The gestation period is approximately 21 days.

Shrews have an acute sense of touch, hearing, and smell, with vision playing a relatively minor role. Some species of shrews use a series of high-pitched squeaks for echolocation, much as bats do. However, shrews probably use echolocation more for investigating their habitat than for searching out food. Glands located on the hindquarters of shrews have a pungent odor and probably function as sexual attractants. Blarina brevicauda, and presumably B. carolinensis and B. hylophaga (the short-tailed shrews), have a toxic venom in their saliva that may help them subdue small prey.

Some shrews are mostly nocturnal; others are active throughout the day and night. They frequently use the tunnels made by voles and moles. During periods of occasional abundance, shrews may have a strong, although temporary, negative impact on mouse or insect populations. Many predators kill shrews, but few actually eat them. Owls in particular consume large numbers of shrews.

Some shrews exhibit territorial behavior. Depending on the species and the habitat, shrews range in density from 2 to 70 individuals per acre (1 to 30/ hectare) in North America.

Damage
Most species of shrews do not have significant negative impacts and are not abundant enough to be considered pests (Schmidt 1984). Shrews sometimes conflict with humans, however. The vagrant shrew (Sorex vagrans) has been reported to consume the seeds of Douglas-fir (Pseudotsuga menziesii), although the seeds constitute a minor part of the diet. The masked shrew (Sorex cinereus) destroyed from 0.3% to 10.5% of white spruce (Picea glauca) seeds marked over a 6-year period (Radvanyi 1970). Lodgepole pine (Pinus contorta) seeds are also eaten by the masked shrew. Radvanyi (1966, 1971) has published pictures of shrew, mouse (Peromyscus, Microtus, and Clethrionomys spp.), and chipmunk (Eutamias spp.) damage to lodgepole pine seeds, and describes shrew damage to white spruce seeds.

The northern water shrew (Sorex palustris) may cause local damage by consuming eggs or small fish at hatcheries. The least shrew (Cryptotis parva), also known as the bee shrew, sometimes enters hives and destroys the young brood. The northern short-tailed shrew (Blarina brevicauda) has been reported to damage ginseng (Panax spp.) roots. Short-tailed and masked shrews reportedly can climb trees where they can feed on eggs or young birds in a nest or consume suet in bird feeders.

The pugnacious nature of shrews sometimes makes them a nuisance when they live in or near dwellings. Shrews occasionally fall into window wells, attack pets, attack birds or chipmunks at feeders, feed on stored foods, contaminate stored foods with feces and urine, and bite humans when improperly handled. Potential exists for the transmission of diseases and parasites, but this is poorly documented.

Economics of Damage and Control
No studies concerning the economics of shrew damage and control are available. In Finland, shrews appear to play a more important role as predators of conifer seeds than they do in North America. Overall, the economics of damage by shrews is not considered great.

Legal Status
Shrews are not protected by federal laws, with one exception. The south-eastern shrew (Sorex longirostris fischeri) is protected in the Great Dismal Swamp in Virginia and North Carolina by the Endangered Species Act of 1973. The following additional species or populations are of concern: Sorex preblei, Sorex trigonirostri, and Sorex merriami in Oregon; Sorex trigonirostri eionis in Florida along the Homossassee River; and Sorex palustris punctulatus in the southern Appalachians.

Some states may have special regulations regarding the collection or killing of nongame mammals. Consult your local wildlife agency or Cooperative Extension office for up-to-date information.


Damage Prevention and Control Methods

Exclusion
Rodent-proof structures also exclude shrews.

Cultural Methods
Mowing may decrease preferred habitat and food.

Repellents
None are registered.

Toxicants
None are registered.

Fumigants
None are registered.

Trapping
Mouse trap (snap trap). Small box trap. Pit trap.

Shooting
Not practical.

Other Methods
Cats may reduce densities around structures. Owls consume large numbers of shrews. Mowed grass around structures may increase predation.




ACKNOWLEDGEMENTS
The above information was adapted from PREVENTION AND CONTROL OF WILDLIFE DAMAGE with permission of the editors, Scott E. Hygnstrom, Robert M. Timm, and Gary E. Larson (Cooperative Extension Division, Institute of Agriculture and Natural Resources University of Nebraska-Lincoln, United States Department of Agriculture Animal and Plant Health Inspection Service, Animal Damage Control, Great Plains Agricultural Council Wildlife Committee).