Shrews

Shrews are very small, secretive, mouse-like mammals that inhabit moist, shady woodland areas. Generally, they have long, flexible, pointed snouts and very small eyes and ears. Their fur is soft and dense, and most species have prominent scent glands. All shrews belong to the Family Soricidae (subfamilies Soricinae, Crocidurinae, Myosoricinae) and Order Eulipotyphia, which also includes moles, shrew-like moles, desmans, gymnures, hedgehogs, and solenodons. True shrews, talpids, and solenodons were formerly grouped in the clade Soricomorpha; however, Soricomorpha has been found to be paraphyletic (descended from a common evolutionary ancestor or ancestral group, but not including all descendant groups). Members of this order are nearly cosmopolitan in distribution, with the exception of Australia, New Zealand, Antarctica, extreme southern South America, New Guinea, and the northern polar region. This order is extremely ancient and includes the earliest placental mammals. Worldwide, there are about 385 species in twenty-six genera, and, in North America alone, there are sixteen species within four genera. In Arkansas, the family is represented by five species, including Crawford’s gray or desert shrew (Notiosorex crawfordi), least shrew (Cryptotis parva), southeastern shrew (Sorex longirostris), northern short-tailed shrew (Blarina brevicauda), and southern short-tailed shrew (Blarina carolinensis).

The subfamily Soricinae collectively refers to the red-toothed shrews. In addition, the family contains four extinct subfamilies, thirteen extant genera, and about thirty-eight species. These species are typically found in North America, northern South America, Europe, and northern Asia. The enamel on the tips of their teeth is reddish due to iron pigment. The iron deposits serve to harden the enamel and are concentrated in those parts of the teeth most subject to wear.

The subfamily Crocidurinae includes twelve genera and about 220 species. These are the so-called white-toothed shrews. Shrews in this subfamily are typically found in Africa, southern Europe, and Asia. This subfamily includes the smallest shrew, the Etruscan shrew (Suncus etruscus), which is about 3.5 cm (1.4 in.) in length and 1.8 g (0.063 oz.) in weight. It is found in warm and damp climates in Europe and North Africa east to Malaysia and is the smallest living terrestrial mammal. The largest species also belongs to this subfamily, the Asian house shrew (Suncus murinus), which is about 15 cm long and weighs around 100 g. It is found in tropical South Asia but has been introduced widely throughout Asia and eastern Africa. The genus Crocidura also belongs to this subfamily and contains the largest number of species of any mammalian genus.

Members of the shrew subfamily Myosoricinae occur exclusively south of the Sahara Desert. The subfamily contains three genera and about twenty species. They are commonly called Congo shrews, forest and mouse shrews, and African mole shrews.

Ecologically, shrews are valued components of any ecosystem. Since they burrow, their foraging activities help enrich and work the soil. In addition, they consume a great variety of insects and other small invertebrates, and in turn, they serve as prey sources for larger animals, especially owls. Shrews are active enough to cover large distances, and adult males may stray widely. Home ranges of shrews are relatively small compared to most mammals.

General characteristics of the Soricidae are as follows: (1) long, pointed nose extending well beyond supporting skull; (2) long, narrow skull lacking zygomatic arches and auditory bullae; (3) first upper incisor in each jaw hook-shaped with a second cusp near its base; (4) three to five simple teeth (unicuspids) behind larger front teeth; (5) upper cheek teeth W-shaped; (6) tibia and fibula usually united; (7) no cecum present; and (8) plush fur.

Shrews feed upon many kinds of small invertebrates, such as earthworms, snails, sowbugs, and myriapods. Some species, however, including the short-tailed shrews (genus Blarina), are large enough to seize and feed on small rodents, salamanders, and other animals of a similar size. In addition, a significant amount of plant material is included in the diet of some species. Shrews have high basal metabolic rates and, as such, are prodigious eaters. Indeed, their food intake per unit body weight is very high, and many species eat more than their own weight per day.

Shrews sometimes make their own runways but usually use those of rodents. They tend to make globular nests consisting mainly of dried grass and leaves and lined with partially shredded grass and leaves. Their nests are located somewhere in their underground tunnel system, usually under a rock, log, or stump. Special places are used for defecation, and the nest is never fouled with fecal material.

In terms of reproduction, shrew breeding seasons may extend year round. With a gestation period of a month or less, there are typically two to nine young in a litter. Young grow rapidly and are weaned at about three weeks of age, when they resemble adults except for their smaller size and sleeker juvenile pelage. Adult size is reached when they are about a month old. Most shrews have a lifespan of three years or less.

Two genera of shrews (Sorex and Blarina) include some of the only terrestrial mammals known to echolocate. They emit series of low-amplitude, broadband, multiharmonic, and frequency modulated ultrasonic squeaks. The sounds contain no “echolocation clicks,” with reverberations that appear to be used for simple, close-range spatial orientation.

Crawford’s gray or desert shrew (N. crawfordi) possesses silver-gray pelage with buff below. It is the only shrew in Arkansas with twenty-eight teeth and conspicuous ears. It is quite rare in the state and has only been reported from seven of seventy-five counties: three in the Interior Highlands (Ozarks) and four in the Gulf Coastal Plain. Desert shrews are generally found in a variety of dry habitats such as desert sagebrush, mesquite-cactus, yucca-cactus, agave-grassland, and the lower edge of pinon-juniper. This shrew is known to live in woodrat (Neotoma) nests, in various kinds of litter, beneath agave plants, and even inside beehives. In Arkansas, the precise status of this shrew is unknown. It is currently listed as Species of Special Concern in Arkansas and has a state ranking of S2 (Imperiled).

The least shrew (C. parva) has a very short tail, only measuring about one-fourth of the total body length. Its pelage is nearly uniform brown or grayish brown above and ashy gray below. An albino C. parva has been reported from Arkansas. The least shrew has thirty teeth, which distinguishes it from other shrews in the state. This shrew is relatively common and occurs throughout most of Arkansas. They are found in open grasslands or old fields and along overgrown fence rows. They also may be found in brushy or marshy areas but seldom, if ever, inhabit mature forests. Evidence that this shrew secretes a poison in its saliva is inconclusive, but earthworms and other prey have been reported to have been paralyzed by its bite. Like other shrews, the least shrew has a very strong odor, which has been described as resembling decayed garlic. This aroma may provide some protection from mammalian predators, but it is evidently not offensive to owls, other avian predators, or snakes.

The southeastern shrew (S. longirostris) has a long (one-third of total body length), indistinctly bicolored tail, which differentiates this shrew from Blarina spp. and other shrews in Arkansas. Its pelage is reddish brown or brownish above and ashy gray washed with pale drab brown below. In Arkansas, this species is rarely collected, and is presently known from relatively few records (all from the Interior Highlands). Specimens have been trapped in dry upland woods and fields, with most captures being from marshy or swampy areas and damp woods, which appear to be the preferred habitat types. This shrew is listed as Species of Special Concern in Arkansas, and its state ranking is S2 (Imperiled).

The northern short-tailed shrew (Blarina brevicauda) is very similar to B. carolinensis and is difficult to distinguish without making comparisons using a large series of specimens, examining a karyotype, or doing molecular analyses. However, it is generally larger and is slate gray to brownish gray above and paler below. It also has a smaller cranial measurement than B. carolinensis. The Arkansas distribution of B. brevicauda, formerly treated as Elliot’s short-tailed shrew (B. hylophaga), is greater than previously thought. However, B. carolinensis is known only from the Interior Highlands (Ozark Plateau and Boston Mountains) in northern Arkansas in Madison, Newton, Pope, Searcy, Sharp and Van Buren counties. It therefore occurs throughout the Ozarks and is replaced by B. carolinensis to the south and east of the Ozark Plateau and Boston Mountains. Interestingly, northern short-tailed shrews captured in Minnesota provided the first evidence of hantaviruses harbored by shrews in the Americas.

The southern short-tailed shrew (B. carolinensis) is a small Blarina that has a stocky body with a very short tail (less than one-third of its total length). It has a long, pointed snout, tiny eyes, and very small external ears concealed by fur. Its pelage is velvety, slate-gray to brownish gray above and paler below. As noted above, because species of Blarina are difficult to distinguish based on morphology alone, genetic analysis may be needed to determine true identity in Arkansas, particularly near contact zones. This shrew is common in the southeastern two-thirds of Arkansas and is most often found in moist deciduous woods or brushy areas; it is less common in meadows, old fields, or swamplands. This species is almost completely nocturnal and has a poor sense of smell and very poor eyesight. It relies mostly upon its acute hearing and highly developed sense of touch to locate prey, avoid enemies, and find its way through its burrow system. Owls, bobcats, foxes, weasels, and house cats frequently prey upon short-tailed shrews (there are several cases of barn owl predation in Arkansas).

Several parasites have been reported from shrews. Coccidians, trematodes, tapeworms, and nematodes are known from North American shrews as well as ectoparasites. In Arkansas, no endoparasites have been reported to date, but ectoparasites are known from two species of Blarina. A flea (Doratopsylla blarinae) was reported from B. brevicauda in Searcy County. In addition, two fleas (Ctenopthalmus pseudagyrtes and Doratopsylla blarinae) and four mites (Echinonyssus blarinae, Glycyphagus hypudaei, Olistrophorus blarina, and Protomyobia blarinae) were reported from B. carolinensis from Union County.

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Chris T. McAllister
Eastern Oklahoma State College