Least shrews are very vocal. They make a variety of high frequency sounds including chirps and clicks, some of which are inaudible to humans. Least shrews also use ultrasonic sounds for tunnel exploration. This form of echolocation may be useful while moving underground, but there is no proof that this species uses sound to hunt. Males and females also communicate through scent. Males announce their presence to females through their scent. Females, however use their scent differently; when females stop producing pheromones, they are ready to mate. When females produce a scent, they are not ready to mate or are pregnant.
Communication Channels: acoustic ; chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; acoustic ; echolocation ; chemical
A national survey in 2007 listed Cryptotis parva as a secure species in the United states. However, the state of Michigan lists least shrews as threatened. Currently, no conservation efforts are in place; little is known as to why populations are declining in Michigan.
US Federal List: no special status
CITES: no special status
State of Michigan List: threatened
IUCN Red List of Threatened Species: least concern
There are no known negative impacts of least shrews on humans.
Least shrews are highly insectivorous and may inadvertently help protect crops from harmful insects. Shrews also aerate soil, which is a benefit to agricultural practices.
Positive Impacts: controls pest population
Because of their burrowing habits, least shrews aerate soil and aid the transport of nutrients within soil. Least shrews can eat up to 100% of their body weight in a day and may contribute to regulation of insect populations. They are also eaten by a variety of predators, such as snakes and owls. Least shrews are known to host various fleas and mites such as Orycteroxenus soricis and Androlaelaps fahrenholzi.
Ecosystem Impact: soil aeration
Commensal/Parasitic Species:
Least shrews have immense dietary needs. They generally eat 60 to 100% of their own body weight every day. Least shrews are largely insectivorous, and their diet primarily consists of insect larva and centipedes. They also have been known to eat snails, spiders, and crickets. Least shrews immobilize their prey by attacking the joints of the organism so they cannot flee. The species has also been known to eat small quantities of fungi and other green plants.
Animal Foods: insects; terrestrial non-insect arthropods; mollusks; terrestrial worms
Plant Foods: leaves
Other Foods: fungus
Foraging Behavior: stores or caches food
Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)
Least shrews, Cryptotis parva, occur in greatest densities in the eastern United States. Their geographical range extends from Florida to New York and reaches as far west as Texas and South Dakota. Least shrews also occur in Central America from northern Mexico to Costa Rica and into Panama.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
Least shrews are most commonly found in open fields with tall grasses or areas with fallen trees and brush that provide protection. Least shrews can also be found in softer soil near saltwater marshes along the Atlantic Coast. Some occur in the forests of Florida, relying on the underbrush for cover. Least shrews have been found at elevations as high as 2,100 m.
Range elevation: 0 to 2,100 m.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: savanna or grassland ; forest ; scrub forest
Wetlands: marsh
Other Habitat Features: agricultural
Least shrews tend to live a little over 1 year in the wild. Captive least shrews live can live about 21 months.
Range lifespan
Status: captivity: 21 (high) months.
Average lifespan
Status: wild: 1 years.
Average lifespan
Status: captivity: 2.6 years.
Least shrews have dense, short hair, which is dark brown to reddish brown on the dorsal side during the winter. During the summer, fur becomes grayish brown in color. They have a bicolored tail, with a darker brown on top and a lighter underside. Least shrews measure 70 to 92 mm in length and usually weigh between 3 and 6 g. Members of this species have two distinct ear holes hidden in their fur. Males and females both have scent glands on their flanks, and females have an extra set in front of their ears. Females have six mammae along the lower body. Least shrews can be distinguished from other closely related species by both their tail length and dentition. The tail of least shrews is relatively short and measures 12 to 26 mm. Unlike related species which have three, least shrews have four unicuspid teeth, though the fourth is very small and hidden.
Range mass: 3 to 6 g.
Range length: 70 to 92 mm.
Sexual Dimorphism: sexes alike
Other Physical Features: endothermic ; bilateral symmetry
Average basal metabolic rate: 0.164 W.
Owls are the most common predators of least shrews. Other common predators include rough-legged hawks, foxes, and snakes. Domesticated house cats and spotted skunks are also known predators. When food is scarce, least shrews may also resort to cannibalism. Their ability to stay camouflaged is the only defense of least shrews against predators.
Known Predators:
Anti-predator Adaptations: cryptic
Mating of least shrews generally occurs within the nest. Females alert all males sharing the nest and males in adjoining areas that they are ready to mate by stopping the release of pheromones from their scent glands. When this scent is absent, males show interest by sniffing both the anal glands and glands located in front of the ears of a female. The male then attempts to mount the female. If she is unreceptive, the female may become aggressive, making loud noises and arching her back. The male then ceases its approach and lays on its back, exposing both its neck and belly until he is ready to make another attempt. Females show signs of receptiveness by lifting their tail and presenting themselves. When more than one male is present, aggression levels determine a male hierarchy, and the most aggressive males mate first. Once mating is complete, males take a dominant station over the female. The mating process on average lasts 3 days.
Mating System: polyandrous ; cooperative breeder
Least shrews may reproduce several times during the mating season, which lasts from February to November. Gestation lasts 21 to 23 days. Females give birth to an average of 5 young per litter, though litters can range from 2 to 7 individuals. Newborn least shrews weigh approximately 0.34 g. Young are weaned at about 23 days of age. Males reach sexual maturity around 43 days of age and females around 40 days.
Breeding interval: Least shrews may breed several times per year.
Breeding season: Breeding of least shrews occurs between February and November.
Range number of offspring: 2 to 7.
Average number of offspring: 5.
Range gestation period: 21 to 23 days.
Average gestation period: 21 days.
Range weaning age: 21 to 23 days.
Average weaning age: 21 days.
Range time to independence: 20 to 30 days.
Average age at sexual or reproductive maturity (female): 40 days.
Average age at sexual or reproductive maturity (male): 43 days.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous ; post-partum estrous
Average birth mass: 0.34 g.
Average number of offspring: 4.5.
Average age at sexual or reproductive maturity (male)
Sex: male: 43 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 40 days.
Female least shrews provide almost a full month of care to their young, which are nursed for 20 to 23 days. Most adult members within the nest take an active role in preventing juveniles from getting lost by carrying them in their mouths. Mothers show panic when separated from their young and, when reunited, gather all young together.
Parental Investment: altricial ; male parental care ; female parental care ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Provisioning: Female, Protecting: Male, Female)
The North American least shrew (Cryptotis parvus) is one of the smallest mammals, growing to be only up to 3 inches long. It has a long pointed snout and a tail never more than twice the length of its hind foot. The dense fur coat 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 Eulipotyphla and should not be mistaken for a member of the order Rodentia. The North American least shrew's eyes are small and its ears are completely concealed within its short fur, giving it 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 it can also tunnel through moist soil in search of food much like moles do. However, it mostly occupies burrows built by other mammals.[4]
Its diet consists of mostly small invertebrates, 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, it will aim for the legs and try to cripple its adversary, and will bite lizards, which are often too large for it to kill, on the tail, which then falls off and provides it with a meal while the lizard escapes. The North American least shrew will also sometimes 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 food.[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, from 25 cm to 1.5 m long, and seldom more than 20 cm below the ground. Most shrews are aggressive towards each other, but this species is a social creature and often cooperates in digging its burrows and often sleeps with other shrews. 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 to keep warm.[4] It will line its burrows with leaves and grass in nests for the purpose of rearing offspring. 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. Its natural predators 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 analysis seems to show the 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, are from the family Soricidae and date 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 four or five ancient subfamilies occurred, 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 genus Cryptotis.[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 in mammals is the testes are found inside the abdominal cavity.[6]
Least shrews are being used in research as emesis models, to see how delta-9 tetrahydrocannabinol 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]
The North American least shrew is listed as endangered in Connecticut and in Pennsylvania. The greatest threat to it is the development of coastal habitat, particularly dunes and marshes.[9]
The North American least shrew (Cryptotis parvus) is one of the smallest mammals, growing to be only up to 3 inches long. It has a long pointed snout and a tail never more than twice the length of its hind foot. The dense fur coat 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 Eulipotyphla and should not be mistaken for a member of the order Rodentia. The North American least shrew's eyes are small and its ears are completely concealed within its short fur, giving it very poor eyesight and hearing.
