Crotalids Rattlesnakes Copperheads Cottonmouths

In the United States, most venomous snakes are members of the subfamily Crotalidae, the pit vipers. The three main genera in this family are Crotalus (rattlesnakes), Agkistrodon (copperheads and cottonmouths), and Sistrurus (pigmy rattler and massasauga) (4,31,32).

Crotalids are called pit vipers because of depression or pit located midway between and below level of eye and nostril on each side of head. They sense heat, which helps them detect prey. They are deaf and have poor vision but perceive vibration and odors. Other distinguishing characteristics of pit vipers include vertical elliptical pupils (also seen in a few non-venomous snakes), a single row of subcaudal scales, and a triangular head. Crotalids and viperids can be distinguished from non-venomous snakes by their two elongated, canaliculated, upper maxillary teeth, which can be folded against the roof of the mouth (4,26,27).

The rattlesnake's most distinguishing characteristic is the rattle at the end of the tail. The rattle is composed of loosely articulated, interlocking, kerati-nous rings that vibrate as a defensive warning, creating a distinctive buzzing sound. Copperheads have triangular orange to rust-colored heads, and cot-tonmouths, also known as "water moccasins," have a distinctive white mouth (4,27).

Crotalids have a well developed mechanism for erecting the fangs and introducing the venom into their prey. The muscles of the jaw cause ejection of the venom through the hollow penetrating fangs, and they can control the amount of venom ejected. About 25% to 75% of stored venom is discharged following a rattlesnake bite, and the entire supply is replenished in 3 to 4 weeks. The striking range is usually equivalent to half the length of the snake. The speed of the strike is approximately 8 feet per second. Crotaline (pit viper) venom is usually injected only into the subcutaneous tissue, although deeper, intramuscular (subfascial) envenomation may rarely occur. So-called "dry bites" may occur in about 20% of strikes for crotalids and 40% to 50% for elapids. Individuals may be envenomated by rattlesnakes thought to be dead, even up to 60 minutes after decapitation. A fatally injured rattlesnake may still produce serious or even multiple envenomations (4,9,26,27,32-34).

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