It's easy to confuse a shrew with a mouse, or vice versa, as they look similar in overall size, proportion and colouration---especially when scampering away to get out of a human's or predator's line of sight. There's a large variety within both mice and shrew species, which inhabit nearly every corner of the world. These two types of rodents do have some striking differences, however, despite any similarities.
Shrews are mammals. They're shy animals and usually stay away from humans, although they have been found inside houses. Shrews have small eyes, and don't see well, but their auditory and olfactory senses are keen. With their longer snout and poor eyesight, they resemble tiny moles. Their ecological purpose is to help incorporate detritus, or raw materials and animal tissues, back into the earth. There are carnivorous, aquatic and poisonous shrews among the 376 shrew species.
Mice are also mammals. Most species of mice like to live in close proximity to humans because our homes come with a ready supply of food. Mice will eat a wide variety of food but have a proclivity for grains and seeds. They don't eat much food in a day---only about 3 grams---but have a tendency to nibble on a wide variety of food if available. Mice have large eyes and are thought to be colour-blind. Their senses of hearing and smell are their sharpest, which makes sense because most mouse species are nocturnal.
Many shrew and mouse species are of similar size. Although the shrew has noticeably smaller eyes than the mouse, they both have poor eyesight. Both also have excellent hearing and sense of smell. Shrews and mice have a shorter lifespan (1 to 2 years), hence they also have ability to reproduce quickly. Both have large litters and the ability to become pregnant once again only hours after giving birth.
Shrews have five-toed feet; mice have four toes. The elongated snout of the shrew makes it look more rat or molelike, whereas the mouse's less pronounced snout makes it distinctly mouselike. There are several species of venomous shrews, but there are no venomous mice. While mice are not carnivorous, many shrew species are. Shrews, although shy, live above ground---usually on the forest floor. Mice tend to dig tunnels or live in walls. While there are mice that live in trees, shrew species have a wider range of habitats, including water. Mice are nocturnal, but shrews tend to feed both day and night.
A History as Pests
Shrews and mice are known for inhabiting people's homes or properties as pests. While mice will invade the kitchen, eating everything from chocolate to cereal, shrews will attack and eat any mice that are present, and possibly pets or wildlife such as birds. Mice defecate the moment they need to, wherever they are. Shrews use one or two specific spots, and in a home, this can mean bad concentrated smells. Unlike shrews, mice are abundant, and effects from their havoc increases accordingly.