Micrurus tener Texas coral snake Pit Vipers The pit vipers have several characteristic features that distinguish them from nonvenomous snakes ( Fig 90.20 ): (i) Two pits (with heat-sensitive organs that assist these poor-visioned reptiles to localize their prey) are located on each side of the head, between the eye and nostril; (ii) the pupils are elliptical and vertically oriented; (iii) two curved fangs or hollow maxillary teeth are folded posteriorly against the palate and advance forward when the pit viper strikes; (iv) the head is relatively more triangular; and (v) the scutes, or scales, on the ventral portion caudad to the anal plate continue in a single row, whereas nonpoisonous snakes have a cleft, or double row The rattlesnake (Crotalus ) is distributed widely throughout most of the United States and is the culprit in approximately 60% of all pit viper attacks Several species are notably more menacing and toxic to humans The large diamondback and gold diamondback (Crotalus adamanteus and Crotalus atrox ) often stand their ground when approached by humans and inflict most lethal snakebites in North America The pygmy rattler and massasauga are considered rattlesnakes because, in common with Crotalus species, they possess a “rattler” on their tail However, these two relatively small snakes are members of the genus Sistrurus and their bites are not as toxic as those of true rattlesnakes The copperhead (Agkistrodon contortrix ) is a common poisonous snake that lives in the Southeast and much of the Northeast, extending westward as far as Texas and Nebraska This snake accounts for approximately 30% of venomous snakebites but, luckily, is seldom a serious threat to life or limb Emergency physicians must become familiar with the particular species in their areas Coral Snakes The relatively passive coral snake is responsible for only 10 to 15 snakebite cases per year in the United States It is a member of the Elapidae family, and unlike pit vipers, it has round pupils, a blunt head, ventral caudal scutes, and lacks pits Unlike the nonpoisonous snakes, the coral snake has two small maxillary fangs The snout of the coral snake is always black and is followed by a yellow ring and subsequent black band Red and black bands then alternate down the approximately 2-ft length of the coral snake, with narrow yellow rings bordering the red band ( Fig 90.21 ) The nonvenomous king snake is often confused with the coral; it has red bands directly bordered by black bands The yellow rings in