The eastern massasauga is a rattlesnake species found in central and eastern North America from southern Ontario in Canada and throughout the Midwestern and Eastern United States. Like all rattlesnakes, it is a pit viper and is venomous; it is the only species of venomous snake in Ontario.

Rattlesnakes are venomous snakes that form the genera Crotalus and Sistrurus of the subfamily Crotalinae. All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small animals such as birds and rodents.