Colubrids is a broad classification of snakes that includes about two-thirds of all snake species on earth. The earliest species of the snake family date back to the Oligocene epoch. With 304 genera and 1,938 species, Colubridae is the largest snake family. Colubrid species are found on every continent except Antarctica. While most colubrids are nonvenomous (or have venom that is not known to be harmful to humans) and are mostly harmless, a few groups, such as genus Boiga, can produce medically significant bites, while the boomslang, the twig snakes and the Asian genus Rhabdophis have caused human fatalities.