Pit viper

Pit viper, predominantly New World venomous snake (family Crotalidae). Pit vipers have a pit on each side of the head, each containing a temperature-sensitive organ that can detect the minute changes in temperature caused by the presence of other animals, enabling the snake to detect and strike at its prey. Pit vipers have fangs that fold back when not in use. Most species give birth to live young. Pit vipers include the copperhead, water moccasin, fer-de-lance, and rattlesnake.