Gray-Banded Kingsnake — Lampropeltis alterna Brown 1902
Other Common Names:Blair’s Kingsnake, Davis Mountains Kingsnake, or simply “alterna”
Spanish Names: Falsa Coralilla Bandeada, Alicante, Alicante Ceniza, Pichicuata, Coralilla, Culebra Real Rayada de Gris
Original Description: Brown, A. E. 1901 . A new species of Ophibolus from western Texas. Proceedings of the Academy of Natural Sciences of Philadelphia 53:612–613. Issued February 6, 1902.
Holotype & Type Locality: Academy of Natural Sciences of Philadelphia 14977, collected by E. Meyenberg [date unknown, but likely during 1901] from the Davis Mountains, Jeff Davis County, Texas (USA). Type locality subsequently restricted to vicinity of Madera Canyon, Little Aguja Canyon, and Big Aguja Canyon, near headwaters of Toyah Creek, Jeff Davis County, Texas, USA.
Etymology: The species name refers to the alternating series of bands in the dorsal pattern.
Scientific Describer: Arthur Erwin Brown (1850–1910), General Superintendent of the Zoological Society of Philadelphia (Philadelphia Zoo). Mr. E. Meyenberg collected snakes from the Davis Mountains of Texas for Brown. In addition to the type specimen of L. alterna, Meyenberg also obtained the first specimen of Bogertophis subocularis (Trans-Pecos Ratsnake), which Brown described (as Coluber subocularis) in 1901. Earlier (1890), Brown described Stilosoma extenuatum (Short-tailed Snake) from Florida.
Distribution: Extreme southeastern New Mexico eastward through the Trans-Pecos region of southwestern Texas, then southward within the boundaries of the Chihuahuan Desert of north-central Mexico (including Coahuila, Durango, Nuevo Leon, and probably northern Zacatecas), but ranging outside the boundaries of the desert near Monterrey, Nuevo León and on the eastern flank of the Sierra Madre Occidental in northern Durango (elev. > 2300 m/7550 ft). In strong contrast to the U.S. portion of the range, the distribution within Mexico is very poorly understood. Snakes from the eastern part of the Mexican range have been found from 1000–1800 m (3280–5900 ft) elevation.
Habitat: In Coahuila and eastern Durango, alterna has been found in rocky (especially limestone) Chihuahuan Desert scrub. However, farther to the west, the species extends onto the eastern slopes of the Sierra Madre Occidental of northern Durango, in a pine-oak community at moderately high elevation.
Growth and Size: Based on specimens obtained from the U.S. part of the range, this species attains a greater size than other mexicana kingsnakes, with adults ranging from 24–48 inches (61–122 cm) in total length, exceptionally longer. Hatchlings start out in the 8.5–11 inch (21.6–27.9 cm) TL range, with captives becoming sexually mature at about 20 months if fed aggressively.
Pattern Variation: Because of the strong interest of hobbyists and herpetologists, details of pattern variation are well documented for the U.S. part of the range. The seeming rarity of alterna within Mexico—likely more the result of vastly reduced search efforts compared to what occurs in west Texas—makes it difficult to place pattern variation in a geographic context. Based on U.S. material, it is clear that L. alterna displays considerable pattern variation (“blairi” and “alterna” morphs being endpoints on a continuum) and that such variation has a strong geographic component (i.e., alterna-morph snakes predominate in the western, more arid part of the range, while blairi-morph individuals are characteristic of the more humid eastern segment). Indeed, experienced collectors often can identify the geographic area from which particular snakes were found, owing to nuances of pattern. The degree of pattern variation is among the highest observed for North American colubrids, and approaches that of the often-remarkable within-litter variation typical of captive-bred L. leonis. Most of the Mexico range contains alterna-morph snakes, with the exception of those at the far eastern portion of the range in the Sierra Madre Oriental, where several blairi-type snakes have been found. Ground color varies as well, mostly reflecting the local geology: high-constrast, light ground color snakes are associated with limestone formations, and darker snakes, often with “busier” patterns occurring on volcanic substrates. Although selection for cryptic and/or disruptive color patterns is obvious, mimicry likely also plays a role in influencing pattern types. Venomous models include Rock Rattlesnakes (Crotalus lepidus) and Trans-Pecos Copperheads (Agkistrodon contortrix pictigaster).
Relationships: Phylogenetic relationships within the mexicana group are still not fully resolved. However, recent studies based on sequences from nuclear genes suggest that alterna is not as closely related to mexicana-group species as was long assumed. On the basis of overall morphology and features of color and pattern, L. alterna was thought to be closely related. Their ranges approach one another, but do not overlap, and morphology and color pattern of each species is generally similar in the region where their ranges come closest to one another at the northern end of the Sierra Madre Occidental. Previously, studies of mitochondrial DNA supported such a relationship between alterna and leonis, but those results have been reevaluated based on a better understanding of the limitations of mtDNA evidence in making phylogenetic inferences. Although it is tempting to suggest that the pattern similarity of southern alterna and northern leonis is indicative of recent genetic contact, caution is warranted, as color and pattern may be poor proxies for revealing lineage histories. As yet, there is not any genetic evidence suggestive of hybridization between these two species.
Conservation Status: Gray-banded Kingsnakes potentially occupy a vast area within the Chihuahuan Desert, most of which is herpetologically underexplored, especially for secretive species like L. alterna. Some areas presumed to constitute habitat for L. alterna have been severely degraded by human activities—areas in or near Monclova, Saltillo, and Monterrey. Thus, while it seems reasonable to assume that certain areas no longer support L. alterna, many other places are sufficiently remote, or the terrain so rugged, as to minimize anthropogenic effects.
Captive Stock: A number of breeders in the U.S. specialize in alterna from specific localities, and offspring are available each year. Our alterna breeding groups comprise a mix of both wild-caught and captive-propagated animals from the following U.S. localities: Hueco Mountains, River Road, Christmas Mountains, Black Gap, W of Alpine (Paisano Pass), and Davis Mountains (Hwy 118 NW of Fort Davis).