All snakes should be treated with respect and left alone regardless of venom. Most venomous species in the U.S. are a type of pit viper, including copperheads and rattlesnakes. There are various ways to identify a pit viper from non-venomous snakes. The physical differences focus on features of the head. Characteristics of the nonvenomous snake are narrow head, no pit between eye and nostril and round pupils. The pit vipers have a triangular shaped head, a prominent pit between eye and nostril and elliptical pupils. There are also tail differences. Of course, close examination of a snake of unknown type can be dangerous. Contact a professional wildlife management technician for positive identification.