The Black-tailed rattlesnake is a medium-sized venomous pit viper species found in the southwestern United States and Mexico. They range in color from yellows and olive greens to browns and black. As their name implies, one of their most distinguishing features is, despite variations in body color, entirely black tail scales. Often, these rattlesnakes have a black band across their eyes extending diagonally down to the corners of their mouth, forming a sort of facial 'mask'. Like other rattlesnakes, they have a rattle composed of keratin on the end of their tail. Each time the snake sheds its skin, a new segment is added to the rattle which is fairly fragile and can easily be broken.
Black-tailed rattlesnakes occur in the southwestern United States in Arizona, New Mexico, and west and central Texas, and Mexico as far south as Oaxaca. They are also found in the Gulf of California on San Estéban and Tiburón Islands. These snakes are primarily terrestrial and inhabit grasslands, savannahs, desert areas, rocky and mountainous areas, as well as high-altitude forested habitats.
Black-tailed rattlesnakes are generally solitary creatures. Their behavior varies over the course of a year. In the spring and fall, they are primarily diurnal. In the summer, they shift to a nocturnal behavior, to avoid the heat of summer. In the winter, Black-tailed rattlesnakes hibernate in dens created and abandoned by other animals, often with other species of snakes. They are variable in their form of locomotion depending on what substrate they need to traverse and will actively change between sidewinding or rectilinear movement. Although these snakes spend most of their time on the ground, they are also very good climbers and expert swimmers. Black-tailed rattlesnakes are considered to be one of the most docile rattlesnakes because of their calm demeanor and curious nature. Bites are accordingly fairly rare. These snakes rely mostly on camouflage to avoid discovery. They normally try to slither away when confronted but will rattle when cornered.
Black-tailed rattlesnakes are considered to be monogamous. They breed in the spring when males follow the pheromone trails of the females. During the breeding season, only one male mates with a female and then stays near her for several days guarding against other males. The female gives birth to 4-12 live young in the summer. Baby rattlesnakes are born around 27 cm (10.5 in) in length and stay with the mother only until they wander off on their own, usually in less than a day or two. Young Black-tailed rattlesnakes become reproductively mature when they are 3 to 5 years old.
There are no major threats facing Black-tailed rattlesnakes at present.
According to IUCN, the Black-tailed rattlesnake is locally common and widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
Black-tailed rattlesnakes are important for their ecosystem as they control populations of pests. These snakes feed on rodents, such as mice, rats, and rabbits that may destroy crops and vegetation.