The Probert Encyclopaedia of Nature

CROTALIDAE

Crotalidae is the 'Pit Vipers' sub-family of reptiles of the sub-order Serpentes (Snakes) comprising some seven genera and 130 species native mainly to the Americas with some found in south and south-east Asia. The members have a large, often triangular head which is distinct from a robust body by a relatively narrow neck. The members are characterized by a 'pit' situated on each side of the head between the nostril and the eye. This 'pit' is actually an infra-red heat sensitive detecting organ which presumably allows the animal to hunt in the dark.
Research Crotalidae