black snake, name for several snakes, not all closely related, that are black in color. In the United States the name is applied chiefly to the black racer and to the black rat snake ( Elaphe obsoleta ), both partly arboreal in their habits. The black rat snake, also called pilot black snake and mountain black snake, is found in the NE United States. Like other rat snakes ( Elaphe species), it is a constrictor and a valuable destroyer of rats and mice. It has shiny, slightly keeled scales and reaches a length of 8 ft (2.4 m). The poisonous Australian black snake belongs to the cobra family and has a hood. The North American black snakes are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Squamata, family Colubridae.