North American Least Shrew

North American Least Shrew
North American Least Shrew[1]
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Soricomorpha
Family: Soricidae
Genus: Cryptotis
Species: C. parva
Binomial name
Cryptotis parva
(Say, 1823)
North American Least Shrew range

The North American Least Shrew (Cryptotis parva) is one of the smallest mammals, growing to be only up to 3 inches long. The North American Least Shrew has a long pointed snout and a tail never more than twice the length of their hind foot. It has a dense fur coat that is either grayish-brown or reddish-brown with a white belly. Its fur becomes lighter in the summer and darker in the winter. Although similar in appearance to several species of rodents, all shrews are members of the order Soricomorpha and should not be mistaken for a member of the Rodentia order. The North American Least Shrew's eyes are small and its ears are completely concealed within its short fur, giving the North American Least Shrew very poor eyesight and hearing.



It is found from the grasslands of southern Canada through the eastern and central United States and Mexico.[3] In Canada, only a small population of this animal has been found at Long Point in Ontario.[4]

The North American Least Shrew mostly dwells in mesic grasslands, marshes, and meadows.[5] Most shrews prefer these wet habitats, but the least shrew will also inhabit dry upland regions.[4] This species can be found in meadows, fields, and weedy areas, where the vegetation attracts its insect diet.[4][6]


This tiny shrew is active at all hours of the day, but mostly at night. Hunting by smell and touch, the North American Least Shrew digs through loose soil and leaf litter for its prey along the surface of the ground. The behavior of captive individuals suggests that it can also tunnel through moist soil in search of food much like moles do. However, it mostly occupies borrows built by other mammals.[4]

Its diet consists of mostly small insects, such as caterpillars, beetle larvae, earthworms, centipedes, slugs, and sow bugs.[4] It will also eat from the corpses of dead animals, and small amounts of seeds or fruits. This shrew will eat its prey whole, but when eating crickets and grasshoppers, the North American Least Shrew will bite off the head of its prey and eat only the internal organs.[4] When fighting a larger creature, the North American Least Shrew will aim for the legs and try to cripple its adversary. The North American Least Shrew will bite lizards, which are often too large for the North American Least Shrew to kill, on the tail, which then falls off and provides the North American Least Shrew with a meal while the lizard escapes. The North American Least Shrew will also sometime live inside beehives and eat all the larvae. It will often share its food with other shrews. It eats more than its body weight each day and is known to store excessive amounts of food for later.[4][7]

The North American Least Shrew makes its home in burrows or shallow runways under flat stones or fallen logs. Its burrows are about 2.5 cm in diameter, form 25 cm to 1.5 m long, and seldom more than 20 cm below the ground. Most shrews are aggressive towards each other, but the North American Least Shrew is a social creature and often cooperates in digging its burrows and often sleeps with other shrews. Anywhere from 2 to 31 of these shrews will live together at a time although it is more common to find them together in the winter months in order to keep warm.[4] It will line its burrows with leaves and grass in nests for the purpose of rearing children. The breeding season extends from early March to late November. Females produce two or more litters each season. Each litter will consist of about three to six young, each one weighing about 0.3 g, which grow quickly and will be adult size in about one month. Litters are born 21–23 days after copulation.[4] When first born, young are deaf, blind, and hairless.[4] At 14 days old, they will open their eyes and have fur. By day 21, they will weigh 4-5 g and weaning will begin.[4] The North American Least Shrew rarely lives more than a year. The natural predators of the North American Least Shrew are owls, hawks, the Red Fox, the Raccoon, skunks, and snakes.[4] The North American Least Shrew will try to defend itself with its venomous saliva.

Evolutionary history

Evolutionary analysis seems to show that shrews evolved from the ancestor Crocidosorex in Europe and crossed over into the Nearctic, consisting of North and Central America, via the Bering Strait (above sea level at the time). The earliest fossils of shrews, Crocidosorex piveteaui, is from the Soricidae family and dates back to the Oligocene epoch, but shrews are thought to have originated in the late Eocene (30-40 million years ago). It is debated whether there were four or five ancient subfamilies, but only two are left today: Soricinae and Crocidurinae. Once the descendants of the Crocidosorex crossed into North America, this subfamily of Soricidae gave rise to the genus Antesorex during the Miocene. In the late Miocene, they split into Adeloblarina and Alluvisorex. From Adeloblarina, two genera, Blarina and Cryptotis, diverged during the Pliocene. The North American Least Shrew species, Cryptotis parva, then arose from the Cryptotis genus.[6]

The primitive features of Cryptotis parva suggest its ancient origins. The zygomatic arches are missing in the skull, which are present in most mammals even of that size, such as rodents. The mandible also has a more primitive structure with a double articulating surface. The cerebral hemisphere is relatively small, which is necessary in manipulative abilities. However, the olfactory lobes are well developed, revealing the significance of the ability to smell in the shrew's survival. The reproductive and urinary systems are joined in one external opening, called the cloaca, which is a primitive character not found in higher mammals. Another trait uncommon to mammals is that the testes are found inside the abdominal cavity.[6]


Least Shrews are being used in research as emesis models. It is being tested to see how delta-9 tetrahydrocannibinol prevents emesis in the cannabinoid receptors. This research is especially useful for cancer patients because chemotherapy drugs, such as cisplatin, cause nausea and vomiting.[8]


  1. ^ Hutterer, Rainer (16 November 2005). Wilson, Don E., and Reeder, DeeAnn M.. ed. Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. (2142 pp.). pp. 273-274. ISBN 978-0-8018-8221-0. OCLC 62265494. 
  2. ^ Woodman, N., Matson, J., Cuarón, A.D. & de Grammont, P.C (2008). "Cryptotis parva". IUCN Red List of Threatened Species. Version 2009.2. International Union for Conservation of Nature. Retrieved 08 February 2010. 
  3. ^ Hutterer, Rainer (16 November 2005). "Order Soricomorpha (pp. 220-311)". In Wilson, Don E., and Reeder, DeeAnn M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. (2142 pp.). p. 273. ISBN 978-0-8018-8221-0. OCLC 62265494. 
  4. ^ a b c d e f g h i j k l Kurta, Allen (1995). Mammals of the Great Lakes Region. University of Michigan Press. 
  5. ^ Hafner, David J. and Carl J. Shuster (May 1996). "Historical Biogeography of Western Peripheral Isolates of the Least Shrew, Cryptotis Parva". Journal of Mammalogy 77 (2): 536–545. 
  6. ^ a b c Churchfield, Sara (1990). The Natural History of Shrews. New York: Cornell University Press. 
  7. ^ Formanowicz, Daniel R. , Jr., Patrick J. Bradley and Edmund D. Brodie, Jr (July 1989). "Food Hoarding by the Least Shrew (Cryptotis parva): Intersexual and Prey Type Effects". American Midland Naturalist 122 (1): 26–33. 
  8. ^ Darmani, Nissar A. and Jennifer L. Crim. "Delta-9-tetrahydrocannabinol differentially suppresses emesis versus enhanced locomotor activity produced by chemically diverse dopamine D2/D3 receptor agonists in the least shrew(Cryptotis parva). Pharmacology Biochemistry and Behavior. Volume 80, Issue 1. January 2005. 35-44.
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