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Abbreviation Legend
- (CE) - Criticially Endangered
- (CI) - Critically Imperiled
- (E) - Endangered
- (I) - Introduced
- (IM) - Imperiled
- (NT) - Near Threatened
- (T) - Threatened
- (V) - Vulnerable
- (**) - Recent Classification Change
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Vipers of the United States
Viperidae in the United States are stout-bodied, with heads that are distinctly wider then the neck and patterned with blotches or crossbands. They have curved, retractable hollow fangs located near the front of the upper jaw. Normally folded back along the jaw, they fangs are quickly swung forward as the mouth is opened to strike. A heat-sensitive pit is present on each side of the head between the eye and the nostril. These are used to locate warm blooded prey. Vipers also have eyes with vertical pupils and an individual row of scales under the tail. Rattlesnakes bear a distinctive rattle on their tail. This unique structure is a series of flattened, interlocking dry horny segments that product a buzzing noise when shaken vigorously. A new segment is added each time the snakes sheds their skin which is 2 to 4 times a year. Vipers appear to be the most highly evolved snakes, organized for capturing, killing, and ingesting relatively large warm-blooded prey. Their venom is a complex mixture of proteins, which act primarily on a victim's blood tissue. Extreme caution is advised as even "road kill" snakes have been known to bite. Most are nocturnal and most bear their young live.
There are only 26 species, belonging to only 3 genus, of Vipers in the United States.
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