Family Viperidae - Vipers
All viperids have a pair of relatively loang erectile hollow fangs at the front of the mouth. When not in use, the fangs fold back and are enclosed in a membranous sheath. The head is distinct and usually covered with small, irregular, overlapping scales. But night adders have large head shields like those of the colubrids. The great majority have vertically elliptical, or slit-shaped, pupils that can open wide to cover most of the eye or close almost completely, which helps them to see in a wide range of light levels.
Almost all vipers have keeled scales (but smooth in night adders), a stocky build with a short tail, and, due to the location of the venom glands, a triangular-shaped head distinct from the neck.
These short to large snakes are mainly terrestrial (some arboreal, one species is a burrowing snake, several are semi-aquatic). Typically, vipers are nocturnal and ambush their prey that is killed by their venom. They feed on small vertebrates.
Most are ovoviviparous, giving birth to live young, but a few lay eggs.Head scales:
Typical vipers have fragmented and keeled scales.
Night adders have smooth colubrid-like scales. Key to Southern African genera in the viperidae: