Pediatric emergency medicine trisk 2015 2015
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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
