This family consists of poisonous snakes. They possess a heat sensitive pit which is located between the eye and nostrils on each side of the face. This pit helps them to sense the body temperature of the nearby predator. The body is slender and covered with keeled scales. The head is large and triangular in shape. The short and moveable maxillary bones, lined with poisonous fangs, no maxillary teeth are present.   

In Pakistan, 1 genus and 1 species of this family is found, which is: