How to Identify the Northern Black-tailed Rattlesnake (Identification Guide)
A guide to identifying this southwestern rattlesnake by its solid black tail, olive-to-yellow body, and diamond-shaped blotches.
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Key identifying features
The northern black-tailed rattlesnake (Crotalus molossus) is a moderately large, heavy-bodied rattlesnake found in the southwestern United States and northern Mexico. Its most distinctive feature, reflected in its common name, is a solid black or very dark tail immediately preceding the rattle, contrasting sharply with the lighter body coloration. It also has a broad, triangular head and a segmented rattle typical of all rattlesnakes.
Coloration & pattern
The body color varies regionally from olive, yellowish-brown, gray, or dark greenish, marked with a series of dark brown to black diamond or blotched markings down the back, often with lighter borders that create strong contrast. Regardless of overall body color, the tail is consistently black or near-black, a trait shared with only a few other rattlesnake species. The head often shows a dark band running diagonally from the eye to the jaw, and the chin and throat area is frequently pale.
Head, eyes & scales
The head is large, broad, and strongly triangular, clearly distinct from the narrower neck, typical of pit vipers. Eyes have vertically elliptical pupils. Dorsal scales are keeled, giving the body a rough texture. A segmented rattle is present at the tip of the black tail, used in defensive displays.
Size & body shape
Adults are moderately large and heavy-bodied, typically reaching 90 to 120 cm in length, with some individuals growing larger. The body is thick and muscular, tapering to the diagnostic black tail and rattle, which stands out clearly against the rest of the body regardless of the snake's base coloration.
Range & habitat where you'll see it
This species is found across the southwestern United States, including Arizona, New Mexico, and Texas, extending into northern Mexico, typically in rocky desert, grassland, and mountainous terrain. It is often found among rock outcrops, canyons, and boulder-strewn slopes at moderate elevations.
How to tell it apart from look-alikes
The solid black tail is the single most reliable feature separating this species from other rattlesnakes in its range, most of which show banded rather than solid-colored tails. Combined with its diamond-patterned body and preference for rocky terrain, the black-tailed rattlesnake is generally straightforward to identify once the tail coloration is observed.
Frequently asked questions
What is the key feature for identifying a black-tailed rattlesnake?
A solid black or very dark tail just before the rattle, contrasting with the lighter, patterned body.
What color is the body typically?
Olive, yellowish-brown, gray, or dark greenish, with dark diamond-shaped blotches often bordered in a lighter color.
Where does this rattlesnake live?
Rocky desert, grassland, and mountainous terrain across the southwestern United States and northern Mexico.
How does the tail help distinguish it from other rattlesnakes?
Most other rattlesnakes in its range have banded tails, while the black-tailed rattlesnake's tail is uniformly dark, making it a distinctive field mark.