Sorex arcticus
Arctic shrew

Arctic shrews, Sorex arcticus, are native to North America. Their distribution ranges as from the Arctic Circle in the north and as far south as the northern United States, into North and South Dakota, Wisconsin, Michigan, and Minnesota. Their eastern limits are in eastern Quebec and the Atlantic Maritime provinces, and their western limits are the southern Yukon and Mackenzie valleys. (Churchfield, 1990; Kirkland and Schmidt, 1996)

Sorex arcticus occupies a variety of habitats, but populations are highest in moist grassy areas near lakes, bogs, swamps, and ditches. Specifically, in the Upper Peninsula of Michigan, arctic shrew populations are the densest in spruce and tamarack swamps, as well as near lakes and streams. They are often found in clearings in boreal forests, as well as marshes. Other occasional habitats include dry fields, old fields, mixed conifer swamps, dense grasses adjacent to ditches, mixed grasses, strawberries and ferns at forest clearings, alder thickets, and dry marsh with grasses, sedge hammocks, forbs, cattail, willow, and red-osier shrubs. (Baker, 1983; Kirkland and Schmidt, 1996; Kurta, 1998)

Arctic shrews are medium-sized shrews with cylindrical bodies. The head is long with a pointed nose, like other shrews. The hair is short and soft, the eyes and ear pinnae are all very small, and the tail is long. (Baker, 1983; Kirkland and Schmidt, 1996)

The mass of S. arcticus ranges from 5.3 to 13.5 g. Total length ranges from 100 to 125 mm. Tail length ranges from 36 to 45 mm. The hind foot length ranges from 12 to 15 mm. (Clough, 1963)

The most distinctive physical characteristic of Sorex arcticus is its coloring. The fur is tri-colored, which is most evident during the winter months. On the dorsal side, from the head to the base of the tail, the fur is very dark brown to black in color. The sides are a lighter brown, and the ventral side of the body is a grayish brown. The tail is bi-colored; the dorsal side of the tail is dark brown and gradually becomes a light brown towards the ventral side. (Baker, 1983; Kirkland and Schmidt, 1996; Kurta, 1998)

Arctic shrews show slight seasonal variation in pelage. Tri-color bands are more distinct during the winter months, from October to June. Like others in the genus Sorex, arctic shrews molt twice a year. Winter fur is thicker and brighter. Summer fur is less insulative and paler. Also, the banded fur pattern is less developed in juveniles. (Baker, 1983; Clough, 1963)

The dental formula for Sorex is I 3/1, C 1/1, P 3/1, M 3/3, with thirty-two teeth total. Teeth have a brownish-red pigment on the tips. Sorex arcticus, like other Sorex, possesses unicuspid teeth after the canines. Arctic shrews have four unicuspids; the first two unicuspids are large and equal in size, and the third is smaller than the first two, but larger than the fourth. (Baker, 1983; Kirkland and Schmidt, 1996)

The metabolic rate of S. arcticus falls between the smaller masked shrew and the larger northern short-tailed shrew. The estimated minimal metabolic rate in S. arcticus is 4.7 kcal per day. (Buckner, 1964; Kirkland and Schmidt, 1996)

In the wild, individual arctic shrews can live as long as 18 months. The juvenile mortality rate is approximately 50% during the first month. (Buckner, 1966)

Sorex arcticus is a solitary species. In one laboratory study, whenever two arctic shrews were placed together in a cage, one was dead within several days. There was no sign of injury to the dead shrew, however. In another laboratory study, arctic shrews were placed in a cage with meadow voles. There was never physical contact between the two species, just alternating behaviors of approach and withdrawal from both animals. (Clough, 1963)

Arctic shrews are active during day and night. There are contradicting reports on levels and cycles of activity throughout the day. One claim is that they are least active between 0600 h and 1000 h, while another reports alternating periods of activity and rest, with an average of fourteen periods of activity daily. (Buckner, 1964; Clough, 1963; Kirkland and Schmidt, 1996)

Arctic shrews are very active and move quickly. Periods of inactivity are spent lying on the ground, either on one side or with the ventral side down, body rolled up, and head tucked under the body. Grooming consists ofwiping the forefeet rapidly along the mouth. (Clough, 1963)

Arctic shrews spend most of their time alone. Two arctic shrews cannot live together in a cage in laboratories, since one always dies. The cause of this is unclear, since the dead shrew has not been injured or bitten. (Clough, 1963)

Home Range

The density of arctic shrews is usually 3 to 5 individuals per acre. Each individual usually limits its activity to 1/10 of an acre. (Baker, 1983; Kurta, 1998)

No information is available specifically for S. arcticus, but in general, olfaction is the strongest and most developed sense in shrews. A large portion of a shrew's brain is devoted to olfaction. (Baron et al., 1983)

Shrews have limited visual ability. The eyes of shrews are very small, and the optic region of the shrew brain is small. (Hutterer, 1985; LeGros, 1932)

Shrews lack fully ossified auditory bullae, but they can produce and perceive sounds in high frequencies. Calls are made for defense and courtship, and calls are also made because of fright. (Branis and Burda, 1994; Hutterer, 1985)

Touch is probably important to shrews. Mothers touch their young, and mates touch each other.

Arctic shrews are insectivorous. Larch sawflies make up a large proportion of the diet. Arctic shrews also eat grasshoppers such as redlegged grasshoppers. Generally, they feed on insect larvae, pupae, and adults, and occasionally other invertebrates. Aquatic insects are also consumed, since arctic shrews sometimes reside near streams and bog banks. In captivity, arctic shrews consume dead voles, fly pupae, and mealworms. (Buckner, 1970; Kurta, 1998)

Sorex arcticus usually forages on the ground, but will also climb plants. Arctic shrews exhibit hunting behavior, preying on grasshoppers. Sorex arcticus has been observed to attack adult Melanoplus ferumrubrum grasshoppers by climbing approximately 31 cm and pouncing on the prey, seizing it with jaws and feet. (Baker, 1983; Buckner, 1970; Jackson, 1961; Kirkland and Schmidt, 1996)

A defense strategy of arctic shrews is excreting a musky scent from its flank glands, a strategy also used in other shrew species. Arctic shrews also remain under cover most of the time and are colored in a waywhich helps to hide them. (Baker, 1983)

The only known predators of arctic shrews are owls. The remains of an arctic shrew have been found in a great horned owl pellet. (Kurta, 1998; Nelson, 1934)

Arctic shrews may have a role in regulating insect pest populations.

In regions where Sorex arcticus and S. cinereus distributions overlap, population sizes are found to be inversely related to each other, suggesting direct competition. (Buckner, 1966)

Sorex arcticus associates with many other small mammals. The most common and frequent ecological associations occur with masked shrews, meadow voles, and northern short-tailed shrews. Other small mammal species that share habitats with arctic shrews are water shrews, pygmy shrews, deer mice, southern red-backed voles, heather voles, southern bog lemmings, meadow jumping mice, ermines, eastern chipmunks, least chipmunks, and red squirrels. (Kirkland and Schmidt, 1996)

Arctic shrews are susceptible to various ectoparasites. These include hypopial mites (Labidophorus soricis), larval ticks (Ixodes muris), myobiid mites (Proomyobia breviseosus and Amorphacarus elongatus), laelapid mites (Androlaelops fahrenholzi), ixodid ticks (Haemaphysalis leporispalustris and Ixodes murinus), Parasitoidea ticks (Euhaemogamasus liponyssoides and Monyssus jamesoni), trombiculid mites (Trombicula harperi) and other Trombicula, myobid mites (Amorphacarus henegerorum), pyemotid mites in the genus Resinacaris, and fleas (Corrodopsylla curvata). (Lawrence, Hays, and Graham, 1965; Whitaker and Pascal, 1971)

There are no known adverse affects of Sorex arcticus on humans.

There are no known positive effects of Sorex arcticus on humans.

Arctic shrews are abundant in suitable habitats throughout their range.

Sorex arcticus is usually referred to as arctic shrews; however other common names are saddle-backed shrews, black-backed shrews, and musaraigne arctique. ("Sorex arcticus", 2006)

There are three subspecies of Sorex arcticus: S. a. arcticus, S. a. laricorum, and S. a. maritimensis. (Kirkland and Schmidt, 1996)

During the Pleistocene, arctic shrews occurred farther south than they do today. The present range of arctic shrew populations was covered by ice during the Pleistocene. Most arctic shrew fossil records are from Pleistocene deposits from the central and southern Appalachian Mountains, and from the Great Plains. Earliest records are from Colorado and Virginia, from the Late Irvingtonian, between 690,000 to 900,000 years before present. (Kirkland and Schmidt, 1996)