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When you think of poisonous animals, you probably think of snakes, jellyfish, spiders and maybe even frogs, certainly not furry mammals. But the animal kingdom is home to a very small variety of poisonous mammals, of which the shrew is one. Strictly speaking, the shrew is venomous rather than poisonous, because it possesses the means to inject its harmful substance—in this case its saliva.
Two species of venomous shrew exist: the Eurasian water shrew and the short-tail shrew. The Eurasian water shrew is roughly the size of a mouse and is often mistaken for one, although it has a distinctive snout that sets it apart from its non-venomous relative. It inhabits riverbanks across the Eurasian plate, from Great Britain to North Korea. The short-tail shrew, which is more toxic, inhabits moist habitats in North America.
Shrews have saliva that is poisonous but that can’t be ingested through the tissue in the mouth, meaning they are effectively immune to their own toxin. Shrews don’t have fangs like snakes, but deliver their poison via a groove in their teeth.
Shrews use their venom to subdue and paralyze their prey. Since they prey on small insects, earthworms and in some cases small mice, the potency of their bite is sufficient to render their prey immobile, but is ineffective on larger animals. They do not use the venom as a means of defense.
Envenomation is very unusual in mammals. The only other mammals capable of envenomation are the slow loris and the platypus. Other mammals are capable of using poisonous substances as a means of defense, for example by coating themselves in a poisonous substance found on a tree or on other animals, but only the shrew, slow loris and platypus can deliver their own venom.
Danger to Humans
Shrew poison does not pose a serious threat to humans. A bite from a shrew would certainly be painful, but the only lasting effects are swelling that lasts for a few days at most.
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