Vipers are venomous snakes that live in every part of the world but Antarctica, Australia, Hawaii, Madagascar, a few Islands, and north of the Arctic Circle. Rattlesnakes are among the most common vipers in North America.

Vipers are known for their ability to track and strike prey. Most vipers are nocturnal. They use heat-sensing pits, organs by their nostrils, to detect warm-blooded animals. When they find prey, they strike quickly and immediately retract their fangs. The prey is not immediately immobilized but continues to move for a time.