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.