It is the second-longest venomous snake after the King cobra.
Black mambas have a coffin-shaped head with a somewhat pronounced brow ridge and a medium-sized eye.
These snakes vary considerably in color, including olive, yellowish-brown, khaki and gunmetal but are rarely black.
The scales of some individuals may have a purplish sheen.
Black mambas have greyish-white underbellies and the inside of the mouth is dark bluish-grey to nearly black.
