The short-tailed shrew is very aggressive and spends most of its time underground, but they can been found indoors in search of food. The short tailed shrew is the largest shrew and only venomous mammal found in North America. Its saliva contains poisons that paralyze its victims. Paralyzed victims may be consumed over a period of a few days. Although this saliva is not poisonous to humans, the bite may cause swelling and pain. If you have shrews indoors let Bug Commander help you!