Vipers and Pitvipers: Viperidae

Vipers and pitvipers are mainly known for the pair of short hollow fangs that usually lie flat in the upper jaw but swing down when the snake opens its mouth to inject its venom. The members of this family are typically rather thick snakes with large triangular-shaped heads, usually catlike eye pupils, and short tails. The tail in a snake is the part of the body behind the vent, a slitlike opening on the belly side of the animal. Those snakes that spend much of their time climbing among shrubs and trees have longer tails. Some vipers and pitvipers have zigzag, diamond-shaped, or other patterns on their backs, but for the most part, vipers and pitvipers have no showy colors and instead simply blend into the background, which often makes them difficult to spot.

The pitvipers are unusual because each has a rattle on the end of the tail and a small but deep pit on either side of the face. The rattle is made of little segments of fingernail-like material that make a noise when they knock against one another. The snake gets a new segment every time it sheds, but the oldest segments frequently fall off. The pits on the snake's face are sensitive to temperature, so the pitvipers have infrared (IN-fruh-red) vision, which is the ability to detect, or to "see," heat.

Vipers and pitvipers come in different sizes. The smallest member of the family is the dwarf puff adder, which grows to about 12 inches (30.5 centimeters). The largest are some of the pitvipers, which reach 11.8 feet (3.6 meters) in length.