The Causinae are a monotypic subfamily of venomous vipers found only in sub-Saharan Africa. It was created for the genus Causus, a group considered to be among the most primitive members of the family Viperidae based on head scalation, oviparity, venom apparatus, and because they have round pupils. However, this is contradicted by recent molecular studies. Six species are currently recognized. They are commonly known as night adders.