Least Shrew
Encyclopedia
The North American Least Shrew (Cryptotis parva) is one of the smallest mammal
s, 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 rodent
s, all shrews are members of the order
Soricomorpha
and should not be mistaken for a member of the Rodent
ia 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.
through the eastern and central United States
and Mexico
. In Canada, only a small population of this animal has been found at Long Point
in Ontario
.
The North American Least Shrew mostly dwells in mesic grasslands, marshes, and meadows. Most shrew
s prefer these wet habitats, but the least shrew will also inhabit dry upland regions. This species can be found in meadows, fields, and weedy areas, where the vegetation attracts its insect
diet.
do. However, it mostly occupies borrows built by other mammals.
Its diet consists of mostly small insects, such as caterpillars, beetle larvae, earthworms, centipedes, slugs, and sow bugs. 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 cricket
s and grasshopper
s, the North American Least Shrew will bite off the head of its prey and eat only the internal organs. 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 lizard
s, 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.
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. 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. When first born, young are deaf, blind, and hairless. 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. The North American Least Shrew rarely lives more than a year. The natural predators of the North American Least Shrew are owl
s, hawk
s, the Red Fox
, the Raccoon
, skunk
s, and snake
s. The North American Least Shrew will try to defend itself with its venom
ous saliva.
, 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.
The primitive features of Cryptotis parva suggest its ancient origins. The zygomatic arch
es 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 system
s 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
.
drugs, such as cisplatin
, cause nausea and vomiting.
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, 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 rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s, all shrews are members of the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Soricomorpha
Soricomorpha
The order Soricomorpha is taxon within the class of mammals. In previous years it formed a significant group within the former order Insectivora...
and should not be mistaken for a member of the Rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
ia 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.
Distribution
It is found from the grasslands of southern CanadaCanada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
through the eastern and central United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. In Canada, only a small population of this animal has been found at Long Point
Long Point
This page relates to a sandspit in Norfolk County, Ontario. For other places called Long Point, see Long Point Long Point is a sand spit on the north shore of Lake Erie, part of Norfolk County in the province of Ontario, Canada. It is about 40 kilometres long and is about a kilometre across at its...
in Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
.
The North American Least Shrew mostly dwells in mesic grasslands, marshes, and meadows. Most shrew
Shrew
A shrew or shrew mouse is a small molelike mammal classified in the order Soricomorpha. True shrews are also not to be confused with West Indies shrews, treeshrews, otter shrews, or elephant shrews, which belong to different families or orders.Although its external appearance is generally that of...
s prefer these wet habitats, but the least shrew will also inhabit dry upland regions. This species can be found in meadows, fields, and weedy areas, where the vegetation attracts its insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
diet.
Behavior
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 molesMole (animal)
Moles are small cylindrical mammals adapted to a subterranean lifestyle. They have velvety fur; tiny or invisible ears and eyes; and short, powerful limbs with large paws oriented for digging. The term is especially and most properly used for the true moles, those of the Talpidae family in the...
do. However, it mostly occupies borrows built by other mammals.
Its diet consists of mostly small insects, such as caterpillars, beetle larvae, earthworms, centipedes, slugs, and sow bugs. 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 cricket
Cricket (insect)
Crickets, family Gryllidae , are insects somewhat related to grasshoppers, and more closely related to katydids or bush crickets . They have somewhat flattened bodies and long antennae. There are about 900 species of crickets...
s and grasshopper
Grasshopper
The grasshopper is an insect of the suborder Caelifera in the order Orthoptera. To distinguish it from bush crickets or katydids, it is sometimes referred to as the short-horned grasshopper...
s, the North American Least Shrew will bite off the head of its prey and eat only the internal organs. 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 lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s, 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
Beehive (beekeeping)
A beehive is an enclosed structure in which some honey bee species of the subgenus Apis live and raise their young. Natural beehives are naturally occurring structures occupied by honeybee colonies, while domesticated honeybees live in man-made beehives, often in an apiary. These man-made...
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.
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. 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. When first born, young are deaf, blind, and hairless. 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. The North American Least Shrew rarely lives more than a year. The natural predators of the North American Least Shrew are owl
Owl
Owls are a group of birds that belong to the order Strigiformes, constituting 200 bird of prey species. Most are solitary and nocturnal, with some exceptions . Owls hunt mostly small mammals, insects, and other birds, although a few species specialize in hunting fish...
s, hawk
Hawk
The term hawk can be used in several ways:* In strict usage in Australia and Africa, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks,...
s, the Red Fox
Red Fox
The red fox is the largest of the true foxes, as well as being the most geographically spread member of the Carnivora, being distributed across the entire northern hemisphere from the Arctic Circle to North Africa, Central America, and the steppes of Asia...
, the Raccoon
Raccoon
Procyon is a genus of nocturnal mammals, comprising three species commonly known as raccoons, in the family Procyonidae. The most familiar species, the common raccoon , is often known simply as "the" raccoon, as the two other raccoon species in the genus are native only to the tropics and are...
, skunk
Skunk
Skunks are mammals best known for their ability to secrete a liquid with a strong, foul odor. General appearance varies from species to species, from black-and-white to brown or cream colored. Skunks belong to the family Mephitidae and to the order Carnivora...
s, and snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s. The North American Least Shrew will try to defend itself with its venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
ous saliva.
Evolutionary history
Evolutionary analysis seems to show that shrews evolved from the ancestor Crocidosorex in Europe and crossed over into the NearcticNearctic
The Nearctic is one of the eight terrestrial ecozones dividing the Earth's land surface.The Nearctic ecozone covers most of North America, including Greenland and the highlands of Mexico...
, 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
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
epoch, but shrews are thought to have originated in the late Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
(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
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
. 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.
The primitive features of Cryptotis parva suggest its ancient origins. The zygomatic arch
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
es are missing in the skull, which are present in most mammals even of that size, such as rodents. The mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
also has a more primitive structure with a double articulating surface. The cerebral hemisphere
Cerebral hemisphere
A cerebral hemisphere is one of the two regions of the eutherian brain that are delineated by the median plane, . The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is...
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
Reproductive system
The reproductive system or genital system is a system of organs within an organism which work together for the purpose of reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes...
and urinary system
Urinary system
The urinary system is the organ system that produces, stores, and eliminates urine. In humans it includes two kidneys, two ureters, the bladder and the urethra.-Kidney:...
s are joined in one external opening, called the cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
, 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
Abdominal cavity
The abdominal cavity is the body cavity of the human body that holds the bulk of the viscera. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm , and its oblique floor is the pelvic inlet...
.
Research
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 chemotherapyChemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
drugs, such as cisplatin
Cisplatin
Cisplatin, cisplatinum, or cis-diamminedichloroplatinum is a chemotherapy drug. It is used to treat various types of cancers, including sarcomas, some carcinomas , lymphomas, and germ cell tumors...
, cause nausea and vomiting.