Which North American shrew has venomous saliva that can immobilize small prey?

The North American shrew whose venomous saliva can immobilize small prey is the northern short-tailed shrew.

The northern short-tailed shrew is Blarina brevicauda, a widespread species of eastern and northeastern North America. Its saliva contains a kallikrein-like protease that can paralyze prey and, in sufficient doses, kill animals somewhat larger than the shrew itself.

The venom is delivered through a specialized arrangement rather than hollow fangs. Submaxillary glands release the toxic saliva into ducts that open near the bases of the lower incisors. The saliva then travels along grooves in those teeth and enters a captured animal during a bite.

This shrew is one of the few venomous mammals, along with solenodons and several other shrews. Its venom is mainly a hunting adaptation, allowing the animal to immobilize prey for storage or later consumption. The bite can also be painful to humans who handle the shrew, although the species is not considered a major human danger.