Smith’s black-headed snake (Tantilla hobartsmithi)

Smith's Black-headed Snake (Tantilla hobarthsmith) is a small snake species that typically measures less than 313mm in total length and less than 238mm in snout to vent length. It exhibits a light brown to tan dorsal coloration, occasionally appearing gray or cream colored. As its name suggests, it is complemented by a distinct dark head cap.

This head cap of Smith's Black-headed Snake is a defining feature, extending from a half scale to three scales behind the posterior end of the furrow between the two parietal scales. Notably, this cap does not extend below the corner of the mouth and often presents with a straight or convex rear border, although it may exhibit irregularities such as concavity or pointedness. Immediately following the head cap, a thin, light collar may be present in approximately 80% of specimens from southern Arizona, though it is often faint. This collar, when observable, does not touch the parietal scales and lacks a bordering dark line or row of spots, while also not extending below the angle of the mouth.

Venturing onto the ventral side, Smith's Black-headed Snake features a gray chin and throat, transitioning into a striking orange, pink, or red stripe running down the belly. This stripe widens and may intensify in color towards the tail, providing a vibrant contrast to the subdued dorsal hues.

Additional morphological features include the absence of a loreal scale and often a lack of contact between the first infralabials. In Arizona specimens, the presence of fewer than 22 gular scales are common, comprising 97% of specimens examined by herpetologists. 15 dorsal scale row count at the midbody is expected. These scales are smooth and devoid of pits.

Sexual dimorphism maybe present in the ventral and subcaudal scale counts but is highly variable, with males typically possessing 124-166 ventral scales and 48-74 subcaudal scales, while females exhibit 130-172 ventral scales and 47-67 subcaudal scales. Both the anal plate scale and subcaudal scales are divided in this species.

Smith's Black-headed Snake exhibits primarily nocturnal behavior, rarely venturing out during daylight hours. It is most active during the night, utilizing its secretive nature to remain hidden beneath the ground's surface. Despite its nocturnal tendencies, the snake may occasionally be encountered on the surface, particularly on moist spring days when near-surface activity increases. During periods of cold weather in late fall and winter, Smith's Black-headed Snake enters a state of hibernation, minimizing activity to conserve energy.

The diet of Smith's Black-headed Snake consists primarily of invertebrates, reflecting its role as a predator within its ecosystem. It preys upon a variety of organisms with elongated bodies, including centipedes, scorpions, millipedes, and soft-bodied caterpillars. Additionally, it consumes beetle larvae and other insects. This species is considered venomous, though not harmful to humans. A pair of grooved teeth, slightly enlarged, are located at the rear of the upper jaw. Venom is delivered through these teeth to incapacitate prey, which consists primarily of invertebrates.   

This species occupies a diverse range of habitats, demonstrating adaptability across various biotic communities. These include brushland, grassland, sagebrush-greasewood, mesquite-yucca, and creosote bush environments. Additionally, it thrives in open chaparral, thornscrub, pinon-juniper woodland, and open coniferous forests. In the eastern part of its range, it extends into persimmon-shin oak, mesquite-creosote bush, and cedar-savanna habitats. The snake's habitat selection often centers around canyon bottoms and stream courses, though it is not restricted to these areas. It seeks shelter beneath rocks, logs, boards, dead yuccas, agave, sotols, and other plant debris, utilizing these microhabitats for refuge and thermoregulation.

Reproduction occurs in the summer months, with females laying clutches of up to three eggs.

Smith's Black-headed Snake exhibits a widely scattered distribution across various regions of the southwestern United States and northern Mexico. In the United States, the snake is primarily found across southeastern Arizona and the sub-Mogollon Rim region of central Arizona. It occupies elevations ranging from 1,500 feet to approximately 5,500 feet above sea level in these areas.

Extending beyond Arizona, Smith's Black-headed Snake ranges across diverse habitats spanning from the south San Joaquin Valley, south Sierra Foothills, and Great Basin Desert in California, eastward through southern Nevada, southern and eastern Utah, to western-central Colorado. Further south, its distribution encompasses southeastern California, southern New Mexico, and western Texas. In Mexico, the snake can be found from the central coast of Sonora, through southeastern Chihuahua, and north into Coahuila.

Within the Arizona portion of the 100-mile circle, Smith's Black-headed Snake is widely distributed, stretching from the Ajo Mountains in the west to the San Bernardino Valley and Swisshelm Mountains in the east, and north to Greenlee County, the Sierra Ancha, and the Sierra Estrella below an elevation of approximately 1860 meters. However, most records of the species stem from lower mountains, bajadas, and valleys, with limited documentation from higher elevations such as the Chiricahua, Mule, Huachuca, Galiuro, Patagonia, or Sierrita mountains.

In the Sonoran portion of its distribution, Smith's Black-headed Snake is known to occur near the northern end of the Sierra Los Ajos. The snake exhibits a secretive nature, often overlooked in many areas due to its elusive behavior. In arid regions within its range, such as the western portion of the 100-mile circle, it is likely restricted to desert mountains, particularly mesic canyons where suitable habitat conditions prevail. Despite its widespread distribution, its secretive nature likely results in underreporting and overlooked populations in various areas.