Vipers are snakes in the family Viperidae, found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, Ireland, and various other isolated islands. All vipers are venomous, and have long (relative to non-vipers), hinged fangs that permit deep envenomation of their prey. Three subfamilies are currently recognized. They are also known as viperids. The name "viper" is derived from the Latin word vipera, -ae, also meaning viper, possibly from vivus ("living") and parere ("to beget"), referring to the trait viviparity (giving live birth) common in vipers like most of the species of Boidae. The earliest known vipers are believed to have diverged from the rest of the clade Caenophidia in the early Eocene.