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Smith’s Black-headed Snake (Tantilla hobartsmithi)
[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2118″ img_size=”large” style=”vc_box_rounded”][vc_column_text]Smith’s Black-headed Snake, Gila Bend Mtns, AZ. Photo by Jim Rorabaugh[/vc_column_text][/vc_column][vc_column width=”1/2″][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]
Description
Tantilla hobartsmithi was described by E.H. Taylor (“1936” 1937) from a single specimen he collected near La Posa, 16 km northwest of Guaymas, Sonora on the night of July 3, 1931. Smith’s Black-headed Snake is a small (< 313 mm TL and 238 mm SVL) and slender snake. The head is not distinct from the neck. It is tan to light brown dorsally with a dark head cap that extends 0.5-3.0 (mostly 1.0-2.0 in Arizona) scales behind the posterior end of the furrow or suture between the two parietal scales. That head cap does not extend below the corner of the mouth and its posterior edge is usually straight or convex, but sometimes concave, irregular, or pointed. There is usually a thin, light collar immediately behind the head cap (present in 80% of hobartsmithi from southern Arizona, but it is often quite faint). When that collar is present, it does not touch the parietal scales (it begins at least a 0.5 scale width posterior to them), it is not bordered by a dark line or row of spots, and does not extend below the angle of the mouth (Cole and Hardy 1981, Wilson and Mata-Silva 2014). There are minute dark spots or maculations on the dorsal scales of nearly all specimens. Ventrally, the chin and throat are gray, followed by orange, pink, or red that manifests as a broad stripe down the belly that becomes wider and may intensify in color towards the tail (Wright and Wright 1957, Ernst and Ernst 2003).
The loreal scale is absent, and the first infralabials are most often not in contact. In Arizona specimens there are usually (97%) fewer than 22 gular scales. Dorsal scale rows number 15 throughout the length of the body, and are smooth and pitless. Males have 124-166 ventrals and 48-74 subcaudals, and females have 130-172 ventrals and 47-67 subcaudals. The anal plate and subcaudals are divided (Cole and Hardy 1981, Wilson and Mata-Silva 2014, pers. obs.). A pair of slightly enlarged, grooved teeth are present in the rear of the upper jaw and may serve to deliver toxins from a Duvernoy’s gland to prey. No subspecies are currently recognized (Crother 2012).
Smith’s Black-headed Snake is most likely to be confused with the three other Tantilla in Arizona and a form of the Western Groundsnake (Sonora semiannulata) that resembles Tantilla. In the 100-Mile Circle, that latter snake is known from the Phoenix area. It has loreal scales, lacks the orange, red, or pink coloration on the venter, and gular scale counts exceed 22. Tantilla wilcoxi and T. yaquia both have bold, broad white collars just posterior to the dark head cap. In the former, that collar almost always touches the parietal scales, and it is bordered posteriorly and often anteriorly by a dark band or a row of dark spots. In T. yaquia there is a distinctive post-ocular white cheek patch, the dark head cap usually extends 0.5-3 scales below the angle of the mouth, and there are few or no dark maculations on the dorsal scales. Distinguishing between Smith’s Black-headed Snake and T. nigriceps can be problematic and there is much overlap in the range of various character traits. However, if the black head cap extends < 1.5 scales beyond the furrow at posterior end of the parietals, it is T. hobartsmithi, or if the cap extends > 3.5 scales beyond that furrow it is T. nigriceps. If the posterior edge of the black cap is straight or concave it is almost certainly a T. hobartsmithi. If a white neck collar is present (may be very faint), it is a T. hobartsmithi. A gular scale count of >22 indicates T. nigriceps. The first infralabials are most often not in contact in T. hobartsmithi, but they usually are in contact in T. nigriceps. Finally, dorsal scales of Arizona T. hobartsmithi are almost always broadly flecked with tiny, dark maculations, whereas Arizona T. nigriceps rarely if ever exhibit this trait. The two differ in distribution and habitat use, as well. However, some specimens, especially in the San Pedro River Valley, defy categorization to one species or the other. Numerous Tantilla specimens in museum collections have been misidentified. In particular, Smith’s Black-headed Snake is often misidentified as T. nigriceps, and Western Groundsnakes that have the Tantilla pattern are often misidentified as Smith’s Black-headed Snake.
Smith’s Black-headed Snake is widely distributed in the Arizona portion of the 100-Mile Circle from the Ajo Mountains east to the San Bernardino Valley and Swisshelm Mountains, and north to Greenlee County, the Sierra Ancha, and the Sierra Estrella below about 1860 m. However, most records are from lower mountains, bajadas, and valleys. There are no records from the Chiricahua, Mule, Huachuca, Galiuro, Patagonia, or Sierrita mountains, and only a few from the Pajarito-Atascosa complex. In the Sonora portion of the Circle, Smith’s Black-headed Snake is only known from near the northern end of the Sierra Los Ajos. This is a secretive species and has no doubt been overlooked in a number of areas. In the arid western portion of the Circle, it is likely restricted to desert mountains, particularly mesic canyons. Throughout its range, Smith’s Black-headed Snake is found from southern California, southern Nevada, southern Utah, western Colorado, portions of Arizona, southern New Mexico and western Texas south to Sonora and portions of Coahuila, Chihuahua, and Nuevo Leon.
In the Circle, Smith’s Black-headed Snake is found in Sonoran desertscrub, Chihuahuan desertscrub, semi-desert grassland, Plains grassland, oak woodland, and marginally into pine-oak woodland. Throughout the Circle, it is often found in riparian situations, but is certainly not restricted to those areas. This is a primarily nocturnal species, rarely seen surface active during the day. It is most often encountered under rocks, logs, and other surface debris. It is probably relatively abundant in some riparian habitats based on the ease of collection in some areas, such as the Verde River northeast of Phoenix. Smith’s Black-headed Snake is rarely found on roads at night. However, they are readily captured in pitfall traps. They are most easily found and captured when conditions are moist. In dry periods and seasons, they become difficult to find and likely burrow deep into soil, burrows, and debris piles. Smith’s Black-headed Snake has been collected every month of the year in the Circle except November, although most are found from March through September.
Smith’s Black-headed Snakes mate in the spring and females lay 1-2 (rarely 3) eggs in May through August (Degenhardt et al. 1996, Goldberg 2004). The smallest sexually mature male and female from Arizona were 138 and 141 mm SVL, respectively (Goldberg 2004). This snake feeds on a variety of invertebrates with elongated bodies, including soft-bodied caterpillars and beetle grubs, as well as scorpions, millipedes, and centipedes (Stebbins 1954; Ernst and Ernst 2003). Captives have eaten mealworms (Stebbins 1954).
Smith’s Black-headed Snake is listed as a species of least concern on the 2014 IUCN Red List. With a valid Arizona hunting license, 20 can be captured per day or held in possession, alive or dead, although take of the species is prohibited without special authorization in protected areas such as National Park Service units. This snake is eliminated in heavily developed agricultural areas and urban environments, and its penchant for riparian areas means it has likely declined with the draining, degradation, and loss of these wetland habitats.
Acknowledgements: Andy Holycross, Tom Brennan, and Randy Babb assisted with the examination of specimens upon which Arizona T. hobartsmithi and T. nigriceps scalation counts and characterizations are based.
Suggested Reading:
Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.
Cole, C.J., and L.M. Hardy. 1981. Systematics of North American colubrid snakes related to Tantilla planiceps (Blainville). Bulletin of the American Museum of Natural History 171(3):199-284.
Cole, C.J., and L.M. Hardy. 1983. Tantilla hobartsmithi. Catalogue of American Amphibians and Reptiles 318:1-2.
Crother, B.I. 2012. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding, seventh edition. Society for the Study of Amphibians and Reptiles, Herpetological Circular (39):1-92.
Degenhardt, W.G., C.W. Painter, and A.H. Price. 1996. Amphibians and Reptiles of New Mexico. University of New Mexico Press, Albuquerque.
Ernst, C.H., and E.M. Ernst. 2003. Snakes of the United States and Canada. Smithsonian Books, Washington, D.C.
Goldberg, S.R. 2004. Reproductive cycle of Smith’s Black-headed Snake, Tantilla hobartsmithi (Serpentes: Colubridae), in Arizona. Western North American Naturalist 64(1):141-143.
Stebbins, R.C. 1954. Amphibians and Reptiles of Western North America. McGraw-Hill Book Company, Inc., New York, NY.
Taylor, E.H. 1937. Notes and comments on certain American and Mexican species of the genus Tantilla with descriptions of new species. Transactions of the Kansas Academy of Science 39:335-338.
Wilson, L.D., and V. Mata-Silva. 2014. Snakes of the genus Tantilla (Squamata: Colubridae) in Mexico: taxonomy, distribution, and conservation. Mesoamerican Herpetology 1(1):5-95.
Wright, A.H., and A.A. Wright. 1957. Handbook of Snakes of the United States and Canada. Volumes I and II. Comstock Publishing Associates, Cornell University Press, New York, NY.
Author: Jim Rorabaugh
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