RATTLESNAKE, common name for poisonous North American snakes,
included among the pit vipers of the viper family, that are recognized
by
a loose, horny rattle at the end of teht ail, which is shaken vigorusly
to
warn off intruders. The rattle is formed when the snake?s skin is shed;
the end
section, or button, of the rattle and an attached ring of the old skin
are retained on
molting. A new ring is added each time the snake molts, which may be as
often as
four times a year. The last ring on the rattle often becomes worn and breaks
off, so
that the number of rattles is not, as popularly believed, an accurate indication
of
age.
Like all pit vipers, the rattlesnake has deep, heat-sensitive pits on the
sides of the
face, which help in hunting warm-blooded prey. Two venom glands, one in
each
cheek, are connected by ducts to the base of two long, hollow fangs that
retract
when not in use. The venom contains at least two poisonous, protein-based
substances. One, a neurotoxin, depresses the action of the heart and lungs;
the
other, a hemotoxin, damages blood vessels and other tissue. Rattlesnakes
feed on
small mammals and reptiles. Like most pit vipers, they give birth from
eggs hatched
inside the mother.
The two genera of rattlesnakes are distinguishable by their head coverings.
Snakes in the genus Sistrurus, which includes the massasauga and the pygmy
rattlesnake, have foreheads covered with
large plates; in the genus Crotalus, the head covering consists of small
scales.
Species of Sistrurus are thick-bodied and sluggish, rarely exceeding 1
m (about 3 ft)
in length. They ranged from southern Canada as far south as Argentina but
have
been nearly exterminated in the U.S. Generally comprised of larger snakes,
the
genus Crotalus in the U.S. includes several well-known species. The timber
rattlesnake (1.5m/5 ft) ranges from Maine to Texas, but its numbers have
been
largely reduced. The eastern diamondback, or water rattlesnake (2 m/7 ft),
is found
in the Southeast; it has a body circumference of about 38 cm (about 15
in). Other
native species include the western diamond rattlesnake, found along the
Mexican
border from Texas to California; the prairie rattlesnake, of the Midwest;
and the red
rattlesnake, of southern and Baja California. The horned rattlesnake, found
in the
deserts of the Southwest, is commonly known as the sidewinder.
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