Find Arctic shrew information at Animal Diversity Web
5.30 to 13.50 g
(0.19 to 0.48 oz)
100 to 125 mm
(3.94 to 4.92 in)
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.
The coloring of arctic shrews is distinctive. The body has three colors of fur, which is most evident during the winter. On the back, from the head to the tail, the fur is very dark brown or black. The sides are a lighter brown. Finally, the belly is a grayish brown. The top of the tail is dark brown which grades into light brown towards under side of the tail.
Arctic shrews molt once per year. The three colored bands of the fur are more distinct during the winter months, from October to June. Winter fur is thicker and brighter thna sumer fur. The banded fur pattern is less developed in juveniles than it is in adults.
Arctic shrews have thirty-two teeth. Their teeth have brownish-red pigment on the tips.
Arctic shrews are found in North America, from the Arctic Circle to the northern United States. They occur in North and South Dakota, Wisconsin, Michigan, and Minnesota. The eastern limits of the species range are in Quebec and the Atlantic Maritime provinces, and the western limits are in the southern Yukon and Mackenzie valleys.
Arctic shrews can be found in a variety of habitats, but populations are highest in moist grassy areas near lakes, bogs, swamps, and ditches. In the Upper Peninsula of Michigan, arctic shrew populations are the densest in spruce and tamarack swamps, as well as near lakes and streams.
These shrews are often found in forest clearings 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.
Although the mating system of arctic shrews is not known for certain, it is likely that they are promiscuous like other shrews.
Arctic shrew females give birth to one or two litters each year.
Breeding occurs from February to August, varying with latitude.
4 to 10; avg. 7
13 to 21 days
20 to 24 days
1 years (average)
1 years (average)
The breeding season can occur from April to August, but may be shorter in the north of the species' range. Arctic shrew females give birth to 1 or 2 litters each year. Litters range from 4 to 10 offspring, with an average of 7 young per litter. Shrews are pregnant for between 13 and 21 days. Females nurse their young for 20 to 24 days. Both female and male arctic shrews reach sexual maturity after one year.
Newborn arctic shrews are helpless. They remain with and are cared for by their mother until the end of the weaning period. The young stay with their mother until 5 to 6.5 weeks after conception. Males play no role in parental care.
18 months (average)
In the wild, individual arctic shrews can live as long as 18 months. The juvenile mortality rate is approximately 50% during the first month.
405 m^2 (average)
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.
Arctic shrews are active both during the day and at night. Some biologists say that they are least active between 6 AM and 10 AM. They seem to alternate periods of activityw ith periods of rest. On average, there are fourteen periods of activity daily.
Arctic shrews are very active and move quickly. When they are not moving, they lay on the ground. They are known to groom by wiping their forefeet rapidly along their mouths.
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.
Shrews have limited visual ability. The eyes of shrews are very small, and the optic region of the shrew brain is small.
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.
No information is available specifically for arctic shrews, but in general the most developed sense in shrews is the ability to smell. These shrews are probably similar, relying on scents to identify foods and other shrews.
Shrews are not able to see very well. Their eyes are very small. The brain of shrews is not wired to allow a lot of complex information from the eyes to be interpreted. Arctic shrews probably do not rely greatly on visual signals, although these may play some role in interactions between individuals.
Shrews can make and hear sounds in high frequencies. Calls are made for defense and courtship. They are also made when an shrew is afraid.
Touch is probably important to shrews. Mothers touch their young, and mates touch each other.
Arctic shrews eat insects. Larch sawflies are a major source of food. Arctic shrews also eat grasshoppers such as redlegged grasshoppers. They often feed on insect larvae and pupae, as well as adults, and sometimes eat other invertebrates. Aquatic insects are also eaten, since arctic shrews sometimes live near streams and bog banks. In captivity, arctic shrews eat dead voles, fly pupae, and mealworms.
Arctic shrews usually hunt for food on the ground, but will also climb plants. They have been seen attacking adult 'grasshoppers Melanoplus ferumrubrum' by climbing up. then pouncing on the prey, seizing it with jaws and feet.
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.
The only known predators of arctic shrews are owls. The remains of an arctic shrew have been found in a great horned owl pellet.
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.
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.
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).
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.
There are three subspecies of Sorex arcticus: S. a. arcticus, S. a. laricorum, and S. a. maritimensis.
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.
Stephanie Seto, University of Michigan
Phil Myers, Museum of Zoology
Nancy Shefferly, Animal Diversity Web
Tanya Dewey, Animal Diversity Web, University of Michigan Museum of Zoology
Baker, R. 1983. Michigan Mammals. Detroit: Michigan State University Press.
Kurta, A. 1998. Mammals of the Great Lakes Region. Ann Arbor: The University of Michigan Press.
Clough, G. 1963. Biology of the Arctic Shrew, Sorex arcticus. American Midland Naturalist, 69: 69-81.
Smithsonian Institution, 1993. "Sorex arcticus" (On-line). MSW Scientific Names. Accessed March 18, 2006 at http://nmnhgoph.si.edu/cgi-bin/wdb/msw/names/query.
Kirkland, G., D. Schmidt. 1996. Sorex arcticus . Mammalian Species, 524: 1-5.
2006. "Sorex arcticus" (On-line). Integrated Taxonomic Information System. Accessed March 18, 2006 at http://www.itis.usda.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=179935.
Churchfield, S. 1990. The Natural History of Shrews. Ithaca, NY: Cornell University Press.
Buckner, C. 1966. Populations and ecological relationships of shrews in tamarack bogs of southwestern Manitoba. Journal of Mammalogy, 47: 181-194.
Whitaker, J., D. Pascal. 1971. External parasites of the arctic shrew in Minnesota.. Journal of Mammalogy, 52: 202.
Lawrence, W., K. Hays, S. Graham. 1965. Arthropodous ectoparasites from some northern Michigan mammals. Occasional Papers of the Museum of Zoology, University of Michigan, 639: 1-7.
Nelson, A. 1934. Notes on Wisconsin mammals. Journal of Mammalogy, 15: 252-253.
Buckner, C. 1970. Direct observation of shrew predation on insects and fish. The Blue Jay, 28: 171-172.
Jackson, H. 1961. Mammals of Wisconsin. Madison: Wisconsin Press.
Baird, D., R. Timm, G. Nordquist. 1983. Reproduction in the arctic shrew, Sorex arcticus . Journal of Mammalogy, 64: 298-301.
Buckner, C. 1964. Metabolism, food capacity, and feeding behavior in four species of shrews. Canadian Journal of Zoology, 42: 259-279.
LeGros, C. 1932. The brain of Insectivora. Proceedings of the Zoological Society of London: 975-1013.
Baron, G., H. Frahm, K. Bhatnagar, H. Stephan. 1983. Comparison of brain structure volumes in Insectivora and Primates III Main olfactory bulb (MOB). J. Hirnforsch, 24: 551-568.
Hutterer, R. 1985. Anatomical adaptations of shrews. Mammal Review, 15: 43-55.
Branis, M., H. Burda. 1994. Visual and hearing biology of shrews. Pp. 189-200 in J. F. Merritt, G. L. Kirkland, R. K. Rose, eds. Advances in the Biology of Shrews, Special Publication no. 18. Pittsburgh: Carnegie Museum of Natural History.
Muller, A., U. Thalmann. 2000. Origin and evolution of primate social organization: a reconstruction.. Biological Review, 75: 405-435.
Stockley, P., J. Searle. 1994. Characteristics of the breeding season in the common shrew (Sorex araneus): male sexual maturation, morphology and mobility. Pp. 181-188 in J. F. Merritt, G. L. Kirkland, R. K. Rose, eds. Advances in the Biology of Shrews, Special Publication no. 18. Pittsburgh: Carnegie Museum of Natural History.