A subfamily of snakes commonly known as pit vipers, crotaline snakes, or pit adders in the family VIPERIDAE. They are distinguished by a deep pit called a fossa or loreal, which functions as a heat-sensing organ located between the eye and nostril on either side of the head.

Synonyms: txid8710, Vipers, Pit, Crotalid, Viper, Pit, Crotalids, Crotalinae, Pit Viper, Pit Vipers