Cryptotis parva
least shrew

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. (Laerm, et al., 2007; Linzey, 1998)

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. (Choate, et al., 1994; Hafner and Shuster, 1996; Hamilton, 1944; Kale, 1972; Laerm, et al., 2007; Linzey, 1998; Schwartz and Schwartz, 1981)

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. (Choate, et al., 1994; Laerm, et al., 2007; Linzey, 1998; Schwartz and Schwartz, 1981; Whitaker, 1974; White and Seymour, 2003)

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. (Choate, et al., 1994; Kivett and Mock, 1980; Schwartz and Schwartz, 1981; Whitaker, 1974)

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. (Choate, et al., 1994; Hayssen, 1993; Kivett and Mock, 1980; Schwartz and Schwartz, 1981; Whitaker, 1974)

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. (Kivett and Mock, 1980; Schwartz and Schwartz, 1981; Whitaker, 1974)

Least shrews tend to live a little over a year in the wild. Captive least shrews, however, can live for roughly 21 months. (Choate, et al., 1994; Laerm, et al., 2007)

Least shrews are very social compared to other shrews. Though uncommon, large colonial settlements of up to 31 shrews in one nest have been found. Although they occasionally take over tunnels created by other small mammals, least shrews are capable of digging their own tunnels, which can range in length from 25.4 to 150 cm. Least shrews have been observed cooperatively digging their tunnels. Nests are generally built within the tunnel system, constructed from a variety of plant matter such as fallen leaves and grasses. Nests are small and round and no more than 20 cm in diameter. They have two or more openings that lead into the tunnel system. Nests have also been found underneath fallen trees and rocks, separate from the tunnel system. (Choate, et al., 1994; Linzey, 1998; Schwartz and Schwartz, 1981)

Least shrews are estimated to be active for 11 hours each day, throughout both the day and night. Activity peaks at night and decreases during extremely hot and cold months. The majority of a least shrew's time is spent staying hidden or hunting. Least shrews share food when feeding on a larger organism. When food is scarce, least shrews have been known to resort to cannibalism. (Choate, et al., 1994; Linzey, 1998; Schwartz and Schwartz, 1981)

Least shrews have a home range of about 0.20 ha. They strictly defends their nest but not their entire home range. (Choate, et al., 1994)

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. (Schwartz and Schwartz, 1981)

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. (Choate, et al., 1994; Laerm, et al., 2007; Schwartz and Schwartz, 1981)

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. (Choate, et al., 1994; Linzey, 1998)

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. (Schwartz and Schwartz, 1981; Whitaker, 1974)

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. (Schwartz and Schwartz, 1981)

There are no known adverse effects of least shrews on humans.

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. (Laerm, et al., 2007)