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Black-Tailed Rattlesnakes - Crotalus molossus

The Black Tailed Rattlesnake is a relatively small rattlesnake species. It averages between 30 and 40 inches long. The female tends to be larger than the male. Black-tailed Rattlesnakes range in color from olive green, to yellow, brown, and black. As their name implies, despite variations in body color, the tail scales are always entirely black. Occasionally these snakes have a black band that goes across their eyes and diagonally down to the corners of their mouth forming a sort of facial ‘mask.’

Range & Habitat

Found in the southwestern United States in Arizona, New Mexico and west and central Texas, and Mexico as far south as Oaxaca. Also found in the Gulf of California on San Estéban Island and Tiburón Island. The distribution reaches a maximum elevation of 2930 m. The type locality given is "Fort Webster, St. Rita del Cobre, N. Mex." (Fort Webster, Santa Rita del Cobre, Grant County, New Mexico, USA).

Behavior

All rattlesnakes are carnivorous, their primary food sources being rodents, other small mammals, birds, and small reptiles. The behavior of Northern black-tailed rattlesnakes 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, they hibernate in dens created and abandoned by other animals, often with other species of snake. They are variable in their form of locomotion depending on what substrate the need to traverse and will actively change between sidewinding or rectilinear movement. Although they are able climbers and expert swimmers, C. molossus is primarily a terrestrial species and inhabits grasslands, desert areas, rocky and mountainous areas, as well as higher altitude forested habitats.

Additional Notes

Breeding occurs in the spring when males follow the pheromone trails of the females. Copulation can sometimes last for hours and happen multiple times over a period of days. After mating, the male often stays near the female for several days to prevent any other males from mating with her. The female gives birth to live young in the summer months, and the babies only stay with the mother only until they wander off on their own, usually less than a day or two. Females are believed to breed every year, and can have litters as large as 10-12 young, but usually averages 4-6. Their lifespan averages 15-20 years.

Subspecies

Subspecies	Common name	Geographic range
C. m. estebanensis	San Esteban Island black-tailed rattlesnake	Mexico: Isla San Esteban (Gulf of California).
C. m. molossus	Northern black-tailed rattlesnake	United States (Arizona, New Mexico, southwest Texas), Mexico
C. m. nigrescens	Mexican black-tailed rattlesnake	Mexico (South Sonora, southwest Chihuahua, southern Coahuila, south to Oaxaca and Veracruz, Tlaxcala)
C. m. oaxacus	Oaxacan black-tailed rattlesnake	Mexico (Oaxaca)