[vc_row][vc_column][vc_column_text]

Yaqui Black-headed Snake (Tantilla yaquia)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2131″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Yaqui Black-headed Snake, Santa Cruz Co, AZ. Photo by Jim Rorabaugh[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2540″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Yaqui Black-headed Snake, Santa Cruz Co, AZ. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

The Yaqui Black-headed Snake (Tantilla yaquia) was described by Hobart M. Smith (1942) based on an adult female (MCZ 43274) collected at Guasaremos on the Rio Mayo, Chihuahua by Howard Scott Gentry in August 1936. The systematics of this snake has not been investigated with molecular genetics, but Cole and Hardy (1981) provided an excellent and detailed review of this species, its morphology, and how it differs from other related, North American Tantilla. No subspecies of T. yaquia are currently recognized (Crother 2012).

This is a small, secretive, and infrequently encountered snake (Figure 1). The University of Arizona collection contains 29 specimens, only 15 of which are from Arizona. In comparison, the collection includes 178 specimens of Smith’s Black-headed Snake (T. hobartsmithi) from Arizona. The Yaqui Black-headed Snake was first collected in Arizona in 1907 at Bisbee, but the specimen was misidentified as a Plain’s Black-headed Snake (T. nigriceps) until reexamined and declared the first T. yaquia from Arizona and the United States by C.J. McCoy in 1964.

Description and Similar Species

The Yaqui Black-headed Snake is a brown, grayish-brown, or tan snake with a maximum total length (body + tail) of 325 mm. Tail length varies from 17.2-28.5% of total length, with the higher percentages characteristic of more northerly populations. Dorsal scales are smooth and occur in 15 rows throughout the length of the body. The anal plate is divided, and the mental scale is usually separated from the chinshields. A dark gray, dark brown, or black head cap extends two to slightly more than four scales behind the posterior end of the suture between the parietal scales, and usually extends 0.5-3 scales below the angle of the mouth. The posterior edge of the cap is usually straight. Posterior to the dark cap is a light collar, 1.0-1.5 scales wide, that is not bordered posteriorly by a dark band and does not contact the parietal scales (primarily in specimens from Mexico, the light collar may be bordered posteriorly by a few dark spots). A large, light cheek patch posterior to the eye and a light stripe on the supralabials below and anterior to the eye are notable and distinctive (Figure 2). The snout is often light-colored or has light spots, as well. Ventral coloration in life is cream grading to light pink or orange posteriorly. In preserved specimens, the ventral coloration fades to light tan, light gray, or gray (Smith 1942; McDiarmid 1968, 1977; Cole and Hardy 1981; Degenhardt et al. 1996; Ernst and Ernst 2003).

The Yaqui Black-headed Snake is most similar to other Tantilla in Arizona (T. hobartsmithi, T. nigriceps, and T. wilcoxi). The large, white cheek patch is a distinctive character that is absent or not as well developed in other Arizona Tantilla. Minute dark spots present on the dorsal scales of Smith’s Black-headed Snake and the Chihuahuan Black-headed Snake (T. wilcoxi) are absent or very small and very few in the Yaqui Black-headed Snake. In the Chihuahuan Black-headed Snake, the light-colored neck collar is in contact with the parietals and is bordered posteriorly by a dark band or a distinct row of spots. The dark head cap does not extend below the angle of the mouth in Smith’s Black-headed Snake, and furthermore, the light collar is commonly absent (in ten of 51 specimens from Pima County, Cole and Hardy 1981), and when present is thin and often faint. The Plain’s Black-headed Snake lacks the light neck collar and the posterior margin of the dark head cap tapers to a point or is convex (sometimes irregularly so) at mid-dorsum. The Ring-necked Snake (Diadophis punctatus) is superficially similar to the Yaqui Black-headed Snake, but it has loreal scales (may be missing on one side – Tantilla lacks loreal scales) and dark spots on the ventral scales. A color phase of the Western Groundsnake (Sonora semiannulata) frequently found in and near Phoenix and the Verde Valley (well north of the range of T. yaquia) resembles Tantilla, but that species also has loreal scales.

Distribution and Habitat Use

In Arizona, the Yaqui Black-headed Snake is known only from Cochise and Santa Cruz counties at elevations ranging from about 1,083 to 1,830 m. In Cochise County, it is been found in the Peloncillo, Dos Cabezas, Chiricahua, Swisshelm, and Mule mountains, as well as sites at the base of the Pedregosa Mountains on Highway 80. In Santa Cruz County, the species is known from the Pajarito/Atascosa, Patagonia, and Santa Rita Mountains, the northern Canelo Hills, “Los Encinos” near Sonoita, and a site just south of the Santa Cruz River near Nogales. A specimen from Kitt Peak in the Baboquivari Mountain (UAZ 45527) is a misidentified Smith’s Black-headed Snake, although it seems likely that T. yaquia occurs in that mountain range. Its apparent absence from the Huachuca Mountains is puzzling, especially given its presence in the adjacent Canelo Hills.  Turner et al. (2003) found Smith’s Black-headed Snake in the Whetstone Mountains, but no Yaqui Black-headed Snakes.  Given its presence in the Mule Mountains, the Dragoon Mountains should be searched for Yaqui Black-headed Snakes.

Elsewhere, the Yaqui Black-headed Snake occurs in the Peloncillo Mountains of Hidalgo County, New Mexico, where it was first reported in 1992 (Painter et al. 1992), and in Mexico in eastern and southern Sonora, western Chihuahua, and Sinaloa southward to the Rio Santiago Valley, Nayarit (McDiarmid 1977, Ernst and Ernst 2003). In Sonora, the species has been found in the mountains west of Nogales, the Sierras El Tigre, de la Madera, and Aconchi, near Aribabi, the Río Aros northeast of Sahuaripa, the Sierra El Aguaje north of San Carlos, and localities near Álamos, at Mirasol, and south of Navojoa. On the coastal plain from Sonora to Nayarit, this species occurs as low as 60 m in elevation. Figure 3 illustrates its distribution in Arizona and Sonora.

In Arizona, the Yaqui Black-headed Snake is primarily a species of oak woodlands in rolling to rugged terrain. However, the species occurs sparingly into semi-desert grasslands, Chihuahuan desertscrub, and pine-oak woodland in Arizona. In Mexico, it also occurs in foothills and coastal thornscrub, tropical deciduous forest, and marginally into Sonoran desertscrub (Sierra El Aguaje, Sonora). Many Arizona localities are in rocky canyons with intermittent or permanent streams, but whether that represents a habitat preference or a collector bias is unknown.

Activity and Behavior

In Arizona, the Yaqui Black-headed Snake has been collected from March-October, with the greatest number encountered in April and August. Activity is extended in southern Sonora, where snakes may be found year round.  This species is mostly found under rocks and occasionally other surface litter, often when the ground is moist from rainfall (McDiarmid 1968). It is frequently characterized as fossorial, but occasionally encountered surface active at night or at dusk. B.R. Tomberlin (in Degenhardt et al 1996) reported finding them occasionally on paved roads after dark near Portal, Arizona during the summer months. They are also taken in pitfall traps, indicating surface activity.

The reproductive biology of this species has not been studied; however, Stebbins (2003) suggests 1-4 eggs are probably laid in late spring and summer. Two recently hatched specimens with umbilical scars measured 104 and 140 mm total length (McDiarmid 1968); the smallest of which was found in January near Álamos, Sonora. Size at maturation is unknown. Females typically possess more ventral scales as compared to males from the same population. McDiarmid (1968) found a Yaqui Black-headed Snake in the stomach of a Tarahumara frog (Lithobates tarahumarae) collected in Alamo Canyon, Santa Cruz County, Arizona.

Diet

The diet of the Yaqui Black-headed Snake has not been investigated; however, authors have speculated that it eats invertebrates, particularly elongated forms such as centipedes and millipedes, and soft-bodied spiders, insect larvae, and other arthropods (Degenhardt et al. 1996, Ernst and Ernst 2003). Goldberg and Bursey (2004) present indirect evidence that a Yaqui Black-headed Snake collected in Santa Cruz County consumed an arthropod.  Enlarged, grooved teeth in the rear of the upper jaw are presumably capable of delivering toxins from a Duvernoy’s gland to prey items.

Conservation

The Yaqui Black-headed Snake is listed as a species of least concern on the IUCN’s 2013 Redlist. Given this species’ fairly broad geographic range over a variety of biotic communities, it is probably fairly safe from most anticipated assaults to it and its habitat. It is vulnerable locally to activities such as hard rock mining (e.g. for copper and gold) that eliminate its habitat, and on a broader scale to the effects of climate change and the spread of non-native plants, which could alter fire regimes and patterns and severity of drought, with potentially adverse effects to Yaqui Black-headed Snake populations.

Literature Cited

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.

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., and C.R. Bursey. 2004. Oligacanthorhynchid Acanthocephalan Cystacanths in the Yaqui Blackhead Snake, Tantilla yaquia (Serpentes: Colubridae) from Arizona.  Journal of the Arizona-Nevada Academy of Science 37(2):83-84.

McCoy, C. J., Jr., 1964. The snake Tantilla yaquia in Arizona: an addition to the fauna of the United States. Copeia 1964:216-217.

McDiarmid, R.W. 1968. Variation, distribution and systematic status of the black-headed snake Tantilla yaquia Smith. Bulletin of the Southern California Academy of Sciences 67(3):159-177.

McDiarmid, R.W. 1977. Tantilla yaquia. Catalog of American Amphibians and Reptiles 198:1-2.

Painter, C.W., P.W. Hyder, and G. Swinford. 1992. Three species new the herpetofauna of New Mexico. Herpetological Review 23:62.

Smith, H.M. 1942. A resume of Mexican snakes of the genus Tantilla. Zoologica (New York) 27:33-42.

Stebbins, R.C. 2003.  A Field Guide to Western Reptiles and Amphibians, third edition. Houghton Mifflin Company, Boston, Massachusetts.

Turner, D.S., P.A. Holm, E.B. Wirt, and C.R. Schwalbe. 2003. Amphibians and reptiles of the Whetstone Mountains, Arizona.  The Southwestern Naturalist 48(3):347–355.

Author:  Jim Rorabaugh

Originally published in the Sonoran Herpetologist 2013 26(3):61-63.  For additional information on this species see Sonoran Herpetologist 2015 (June):19-20.

[/vc_column_text][/vc_column][vc_column width=”1/6″][/vc_column][/vc_row][vc_row][vc_column][gap size=”30px” id=”” class=”” style=””][/vc_column][/vc_row]