Sistrurus tergeminus, also known as the western massasauga, is a rattlesnake found in the southwestern plains of the United States and northern Mexico.

[7][8] It is also found in Mexico, in the states of Tamaulipas, southern Nuevo León, north-central Coahuila, and Samalayuca, Chihuahua.

[2] They are primarily found in grassland areas, on the edge of open woodland, or on rocky hillsides, and often make use of the burrows of other animals for shelter.

Their rattles are significantly higher pitched than those of larger species of rattlesnake, sometimes giving them the nickname "buzztail", and as such should not be relied upon for warning.

Primarily nocturnal, the species is considered mild-mannered and sluggish especially during the summer, when the weather is too hot for them to be active and they are sometimes found out sunning themselves.