How to Identify the Mexican West Coast Rattlesnake (Identification Guide)
A guide to recognizing this large, dark-diamond-patterned rattlesnake native to Mexico's Pacific coastal lowlands and foothills.
Read the full Mexican West Coast Rattlesnake encyclopedia entry →
Key identifying features
The Mexican West Coast Rattlesnake (Crotalus basiliscus) is identified by its large size, olive to yellowish-tan body color, and a series of bold, dark diamond blotches with pale edges running along the back. Combined with its heavy build and distribution along Mexico's Pacific slope, this makes it one of the most impressive and readily identifiable rattlesnakes in the region.
Coloration & pattern
Background coloration ranges from olive-green to yellowish-brown or tan. A row of large, dark brown to blackish diamond-shaped blotches, each bordered by a thin pale line, extends down the length of the back, becoming banded toward the tail. The overall pattern is bold and well-defined, particularly in younger individuals, though it can become duskier and less distinct with age in some adults.
Head, eyes & scales
The head is large, broad, and strongly triangular, clearly wider than the neck, with a heat-sensing pit between each eye and nostril. Pupils are vertically elliptical. A dark stripe typically runs diagonally from behind the eye to the corner of the mouth. Dorsal scales are keeled, giving a rough surface texture consistent with other large rattlesnakes.
Size & body shape
This is one of the largest rattlesnake species, with adults commonly reaching 1.5 meters (about 5 feet) and occasionally exceeding 2 meters (6.5 feet). The body is thick and heavily built, tapering to a tail equipped with a large, well-developed segmented rattle capable of producing a loud buzzing sound.
Range & habitat where you'll see it
This species is found along the Pacific coastal lowlands and adjacent foothills of western Mexico, from Sonora south through Sinaloa, Nayarit, Jalisco, and into Michoacán and Colima. It inhabits a range of environments including tropical deciduous forest, thorn scrub, and rocky foothill terrain, generally at lower to moderate elevations.
How to tell it apart from look-alikes
Its large size and bold, pale-edged dark diamond pattern distinguish it from most other Mexican rattlesnakes. It can be confused with the Mexican Lance-headed Rattlesnake, but the Mexican West Coast Rattlesnake is typically larger and heavier bodied with a more olive or yellowish-brown tone, while lance-headed forms tend to differ in pattern detail and geographic range. Its coastal and foothill Pacific distribution, combined with its substantial size, helps separate it from smaller or more inland rattlesnake species found elsewhere in Mexico.
Frequently asked questions
How large does the Mexican West Coast Rattlesnake get?
It is one of the largest rattlesnake species, with adults typically reaching about 1.5 meters (5 feet) and occasionally over 2 meters (6.5 feet).
What pattern does it have?
It has a row of large, dark, pale-edged diamond blotches running down an olive to yellowish-tan body, becoming banded near the tail.
Where is this species found?
It occurs along the Pacific coastal lowlands and foothills of western Mexico, from Sonora south through Jalisco and into Colima and Michoacán.
What habitat does it prefer?
Tropical deciduous forest, thorn scrub, and rocky foothill terrain at lower to moderate elevations.
Is it venomous?
Yes, it is a venomous pit viper and one of the largest rattlesnake species found in Mexico.