North American Least Shrew, Cryptotis parva

The North American least shrew (Cryptotis parva) has a range including Mexico, the United States, and southern Canada. It has been found in a small population at Long Point in Ontario Canada. This shrew prefers to nest in meadows, mesic grasslands, fields, and marshes. As with most shrews, the North American least Shrew prefers moist habitats, but it will also nest in dryer areas. Its habitat is dependent on vegetation that allows for insects for its diet.

At three inches long maximum, the North American Least Shrew is one of the smallest mammals alive. This shrew has a tail length that never reaches more than twice the size of one hind foot. Its belly is white and its thick fur is colored burnished or ashy brown. During the summer, the fur will become lighter. Its snout is elongated and pointy, and its eyes and ears are very small. This gives the shrew poor eyesight and hearing abilities.

The North American least shrew will burrow under logs or flat stones, and they will also use shallow runways as homes.  These burrows can be between 9.8 inches to 59 inches long, and can have a diameter of up to .98 inches. It is rare to find a burrow that is deeper than 7.8 inches. Captive shrews have shown the ability to tunnel through soil, like moles, to search for food, but they prefer to inhabit burrows that were already made rather than digging their own.

Contrary to the behavior of most shrews, the North American least shrew is rather social creature, cooperating with other shrews to dig burrows. Often times these shrews will share burrows. Shrews will live in groups of up to thirty-one, but these larger groups are apt to occur in winter.

The diet of the North American least shrew diet consists of smaller insects like centipedes, slugs, beetle larvae, earthworms and sow bugs. It has also been known to eat carcasses of small animals and small amounts of fruits or seeds. When eating crickets or grasshoppers, this shrew will bite of the insects head and eat only the insides. It eats the entire body of all other insects comprising its diet. This shrew is active throughout the day, but it is most active at night. It will sift through soil and leaf litter in order to find its food.

The breeding season for this shrew will last from March to November, and females can produce up to two litters per season. The litters can contain between three to six young, which weigh a mere .01 ounces at birth and are blind, deaf, and helpless. They will grow quickly, however, reaching adult hood at about one month. This shrew does not usually live past a year. Its predators include the Red Fox, owls, hawks, skunks, snakes, and raccoons. One defense mechanism this shrew has is slightly venomous saliva. When in combat, the North American least shrew will attack the legs of its opponent, aiming to maim and kill rather than overcome to kill. When fighting lizards, which are typically too big for the shrew to kill, it will bite off the tail providing a meal and a means of escape. Shrews will eat up to twice their weight in food each day, and are known food hoarders.

It is thought that the North America least shrew evolved from a European ancestor, called Crocidosorex. Fossils have been found from the Oligocene era that place the early shrews (Crocidosorex piveteaui) in the Soricidae family. This contradicts the belief that shrews originated between thirty-forty million years ago, during the Eocene. From studying early shrew fossils, a direct evolutionary line has been discovered. Out of four to five different possible subspecies of shrew, only two exist today; these are Soricinae and Crocidurinae. After the descendants arrived in North America, using the then exposed Bering Strait, the genus Antesorex branched out from them during the Miocene era. This genus broke into two separate genera, Adeloblarina and Alluvisorex. From Adeloblarina, Blarina and Cryptotis were formed. After this, Cryptotis parva was formed from the Cryptotis genus.

The features of Cryptotis parva are basic, showing just how ancient the species was. The shrew did not have cheekbones, or zygomatic arches, which most mammals (even mammals of such a small size) have. The jawbone, or mandible, also has primitive features, having a double-jointed surface. The cerebral hemisphere area of the brain is rather small, showing that its ability to manipulate objects surrounding it was poor. However, Cryptotis parva had a good sense of smell, due to its developed olfactory lobes. Two traits uncommon to mammals were present in this shrew: the cloaca, were joined externally, where the reproductive and urinary systems, and the testes were found within the  abdominal cavity.

The conservation status of the North American least shrew is of least concern, and it is an important resource in research being done on emesis, or vomiting. These tests are being done to see how the cannabinoid receptors react to the delta-9 tetrahydrocannibinol (THC) in cannabis. This research is important in the medical world for cancer patients, whose chemotherapy causes nausea and vomiting.

Image Caption: Cryptotis parva. Exhibit Museum of Natural History, University of Michigan, 1109 Geddes Avenue, Ann Arbor, Michigan, USA. Credit: Wikipedia