A coiled and unhappy Ridge-nosed Rattlesnake

''Crotalus willardi'' is a venomous pit viper species found in the southwestern United States and Mexico. It is the most recent rattlesnake species to be discovered in the United States. Its specific name is in honor of its discoverer, Professor Frank C. Willard. Five subspecies are currently recognized, including the nominate subspecies described here. The Arizona ridge-nosed rattlesnake is the state reptile of Arizona.