"Northern Short-tailed Shrews have poisonous saliva. This enables them to kill mice and larger prey and paralyze invertebrates such as snails and store them alive for later eating. The shrews have very limited vision, and rely on a kind of echolocation, a series of ultrasonic ""clicks,"" to make their way around the tunnels and burrows they dig. They nest underground, lining their nests with vegetation and sometimes with fur. They do not hibernate. Their day is organized around highly active periods lasting about 4.5 minutes, followed by rest periods that last, on average, 24 minutes. Population densities can fluctuate greatly from year to year and even crash, requiring several years to recover. Winter mortality can be as high as 90 percent in some areas. Fossils of this species are known from the Pliocene, and fossils representing other, extinct species of the genus Blarina are even older."

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account