Most snakes indigenous to the United States are not poisonous. The exceptions are copperheads, coral snakes, rattlesnakes, and water moccasins [source: CDC]. If you're bitten by one of these snakes, seek medical attention immediately, as the venom could be life threatening [source: Mayo Clinic].

Most poisonous snakes in the United States can be identified by the following characteristics:

  • Slit eyes. The only exception is the coral snake.
  • Triangle-shaped head
  • Depression between the eyes and the nostrils [source: Mayo Clinic]

In addition to these general characteristics, each type of snake has its own distinctive features.

  • Copperheads range in color from red to gold, with hourglass shapes on its body [source: CDC]. Young copperhead snakes have a tail with a bright yellow tip. These snakes can grow as large as 24 to 40 inches (61 to 102 centimeters) long, and are usually found in the Eastern United States [source: Andrews, Willson].
  • Coral snakes have colorful red, yellow, and black rings, with the red and yellow rings touching each other. These snakes are usually slender and about 18 to 30 inches (46 to 76 centimeters) long, although they are sometimes a bit longer [source: Barrentine]. Unlike the other venomous snakes, coral snakes don't have slit eyes [source: Mayo Clinic]. These snakes can be found in the Southern United States [source: CDC].
  • Rattlesnakes are the most common type of poisonous snake, and can be found all over the United States. There are 32 different types of rattlesnakes, all with their own identifying features. One thing all rattlesnakes have in common is a tail that makes a rattling sound when the snake feels threatened [source: CDC].
  • Water moccasins, also known as cottonmouths, can be totally brown or black, or can have yellow cross bands. Younger snakes are usually more colorful, and sometimes have a yellow-tipped tail. These snakes can grow quite large. Adult water moccasins are often 24 to 48 inches (61 to 122 centimeters) long, and are sometimes even longer [source: Andrews]. Water moccasins can be found in the Southeastern United States, near rives and lakes [source: CDC].