Black-tailed rattlesnake (Crotalus molossus)

The Black-tailed Rattlesnake, is a sizable serpent, measuring between 28 to 54 inches (71 to 137 cm) in total length, with females typically outsizing the males. Its distinctive feature lies in its tail and sometimes snout, which are black, creating a stark contrast with the rest of its body. Often, these snakes exhibit a distinct black band across their eyes, extending diagonally down to the corners of their mouths, creating a facial 'mask' effect. Occasionally, the tail may exhibit vague gray rings. Its dorsal side is adorned with irregularly outlined black or brown blotches or crossbands, each bordered with whitish edges and featuring a single or double patch of light scales at the center. Towards the front and middle of its back, dark markings sometimes take on a diamond-shaped appearance. The scales in these patterned areas are typically of a uniform color, lacking partial dark or light shading. The ground color of this species varies, ranging from cream, yellow, and grayish to olive, greenish, or dark rust. In environments characterized by dark lava flows, individuals with darker coloration are common.

Distinctively, the Black-tailed Rattlesnake sports enlarged scales on the upper surface of its snout and keeled scales arranged in 27 rows. Juveniles often exhibit dark rings on their tails.

Like other rattlesnakes, the Black-tailed Rattlesnake possesses a rattle composed of keratin at the end of its tail. With each skin shedding, a new segment is added to the rattle. However, the rattle's length does not reliably indicate the snake's age, as it can be broken, and individuals shed their skin multiple times a year.

The Black-tailed Rattlesnake (Crotalus molossus) is distributed extensively across the southwestern United States and parts of Mexico. Its range spans from northern Arizona to the southern edge of the Mexican plateau, extending westward to central Texas. Within Arizona, it is prevalent throughout much of the state, with the exception of the northeastern plateau region. Western Arizona serves as a significant habitat, including areas such as Ajo, Kofa, Castle Dome, and the Hualapai Mountains.

This species demonstrates adaptability in its habitat preferences, inhabiting diverse landscapes ranging from the arid deserts of the southwestern regions to the elevated sky islands of southeastern Arizona. Elevational distribution varies widely, from sea level environments to elevations exceeding 9,600 feet (2,930 m). Notably, sightings have been recorded at high altitudes, such as 6,900 feet at the McDonald Observatory in the Davis Mountains of West Texas.

Beyond the United States, the Black-tailed Rattlesnake's range extends into Mexico, reaching as far south as Oaxaca. It also occupies the Gulf of California, specifically on San Estéban and Tiburón Islands.

The habitat range of the Black-tailed Rattlesnake encompasses a diverse array of biotic communities, showcasing its adaptability across various ecosystems. From the arid landscapes of the Sonoran Desertscrub to the lower regions of Petran Subalpine Conifer Forest, this species demonstrates its ability to thrive in contrasting environments. However, it appears to exhibit a preference for woodland habitats, or elevated terrain, commonly inhabiting hilly or mountainous regions rather than flat expanses, such as barren desert areas. Its presence is frequently observed in areas characterized by rockslides, outcrops, and proximity to cliffs. Stream courses also serve as favored locations, providing both shelter and potential prey opportunities.

The Black-tailed Rattlesnake displays a flexible activity pattern, being active during both day and night under favorable conditions. During spring and fall, it tends to be most active during the day and at dawn or dusk, transitioning towards increased crepuscular and nocturnal activity during the hotter summer months to avoid extreme temperatures. During winter, it hibernates in dens, often shared with other snake species.

Despite its venomous nature, the Black-tailed Rattlesnake is known for its relatively docile temperament, often attempting to retreat rather than confront threats. When it does feel threatened this species, predominantly a ground-dweller, exhibits a rapid rattling response at the indication of danger, often relying on this behavior to signal its presence. Utilizing specialized heat-sensing pits located on each side of its face, it effectively detects warm-blooded predators and prey, a trait common among pit vipers. Bites are infrequent, as the snake typically relies on camouflage to evade detection and resorts to rattling only when cornered or threatened, contributing to its overall survival strategy in various habitats.

Adaptable in its locomotion, this species can switch between sidewinding and rectilinear movement depending on the terrain it navigates. While proficient climbers and swimmers, it primarily inhabits terrestrial environments such as grasslands, deserts, rocky areas, and mountainous regions, including high-altitude forests.

The Black-tailed Rattlesnake employs venom injected through its long, hollow, retractable fangs to kill and initiate the digestion process in its prey. Its diet consists primarily of mice, rats, rabbits, and other small mammals, along with birds and lizards. This carnivorous feeding behavior allows the rattlesnake to sustain itself within its ecosystem, preying on a variety of smaller animals to meet its nutritional needs.

Breeding season for the Black-tailed Rattlesnake occurs in the spring, initiated as males track the pheromone trails of receptive females. Copulation sessions may extend for hours and repeat over several days. Following mating, males often remain in close proximity to females to deter other potential suitors.

 During the summer months, typically in July to August, females give birth to live young. Litter sizes can vary, ranging from 3 to 16 offspring, with larger litters being less common. The female diligently protects her brood until after their first molt, after which the young snakes begin to explore independently.

(Black tailed rattlesnakes and Tiger rattlesnake interaction)

Resources:

McGinnis, S. M., & Stebbins, R. C. (2018). Peterson Field Guide to Western Reptiles and Amphibians. Houghton Mifflin Harcourt.

Brennan, T. C. (n.d.). Black-tailed Rattlesnake. The reptiles and amphibians of Arizona. https://reptilesofaz.org/snakes-subpages/h-c-molossus/

Western black-tailed rattlesnake (crotalus molossus). iNaturalist. (n.d.). https://www.inaturalist.org/taxa/515948-Crotalus-molossus