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Shrew

life science Maturity 5-7 Next article →

Shrews are small, mole-like mammals belonging to the family Soricidae. They are members of the order Eulipotyphla. While they look like long-nosed mice, they are not rodents. Instead, they are more closely related to hedgehogs and moles. Shrews are part of the Boreoeutheria magnorder, a group that includes rodents. However, their teeth tell a different story. Rodents have incisors that grow throughout their lives for gnawing. Shrews have sharp, spike-like teeth that wear down over time.

NShortTailedShrew23
NShortTailedShrew23

The shrew family is incredibly diverse. There are 385 known species in the Soricidae family. This makes them the fourth-most species-diverse mammal family in the world. Only the muroid rodent families and the bat family, Vespertilionidae, have more species. Shrews are found almost everywhere on Earth. They are native to most major land masses. The only major areas without native shrews are Australia, New Zealand, New Guinea, and South America. However, some shrews live in the northern Andes of South America due to the Great American Interchange.

Watershrewskeleton
Watershrewskeleton

Shrews have very unique physical traits and biological processes. They have small eyes and generally poor vision. To make up for this, they have excellent senses of hearing and smell. Most shrews are terrestrial, meaning they live on land. They forage in leaf litter and dense vegetation for seeds, insects, worms, and nuts. Some species have specialized lifestyles. They may climb trees, live underground, or live under snow. Some even hunt in the water.

Watershrewskeleton
Watershrewskeleton

Energy management is a constant struggle for a shrew. They have unusually high metabolic rates. This means their bodies use energy much faster than other small mammals. Because of this, they must eat almost constantly. In captivity, shrews can eat up to two times their own body weight in food every day. They do not hibernate, but some species enter a state called torpor. In winter, many species undergo morphological changes to save energy. They can lose between 30% and 50% of their body weight. This process even shrinks the size of their bones, skull, and internal organs.

Watershrewskeleton
Watershrewskeleton

Their teeth are another fascinating biological feature. Shrews lose their milk teeth before birth. This means they only have one set of teeth for their entire lives. To help these teeth last, some species have iron in their teeth. This iron makes the exposed areas dark red. The iron reinforces the tooth surfaces against the stress of constant eating. This is an adaptation seen only in shrews with high metabolisms. Only rodents have pigmented enamel in their incisors.

Watershrewskeleton
Watershrewskeleton

Some shrews possess rare abilities, such as venom and echolocation. Certain species are venomous, which is unusual for mammals. They do not use fangs to deliver venom. Instead, they use grooves in their teeth to guide it into prey. The venom of the American short-tailed shrew is very strong. Its glands contain enough venom to kill 200 mice if injected. Scientists study this venom for medical uses. Compounds in it might help treat high blood pressure, migraines, or ovarian cancer.

NShortTailedShrew23
NShortTailedShrew23

Additionally, some shrews are among the few terrestrial mammals that use echolocation. This includes the genera Sorex and Blarina. They emit ultrasonic squeaks to sense their surroundings. Unlike bats, they do not use these sounds to pinpoint specific food. Instead, they use them for close-range spatial orientation. They use the echoes to understand their habitat type. This is similar to how a human perceives sound in a large, echoing room.

NShortTailedShrew23
NShortTailedShrew23

Shrew social behavior and reproduction are also very intense. They are fiercely territorial and only meet others to mate. Female shrews are highly productive. They can have up to 12 litters a year in tropical regions. In temperate zones, they only stop breeding during the winter. Their gestation periods last between 17 and 32 days. A mother may become pregnant again within a day of giving birth. They often nurse one litter while the next is being born. Young shrews show a behavior called "caravanning." In this process, babies form a line and grip the fur of the tail of the shrew in front of them.

NShortTailedShrew23
NShortTailedShrew23
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File:Watershrewskeleton.jpg
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