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 [1902]. 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). 

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. Meyenburg collected snakes from the Ft. Davis Mountains of Texas for Brown. In addition to the type specimen of L. alterna, Meyenburg also obtained the first specimen of Bogertophis subocularis (Trans-Pecos Ratsnake), which Brown described (as Elaphe 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. The handful of Mexican specimens of L. alterna mostly fall under the alterna pattern class, although a single specimen obtained from the outskirts of Monterrey (NL) is a blairi morph. 

Relationships: Phylogenetic relationships within the mexicana group are still not well understood. On the basis of overall morphology and features of color and pattern, L. alterna is perhaps most similar to L. leonis (= L. mexicana “thayeri”). The ranges of these two approach closely at the northern end of the Sierra Madre Oriental southeast of Saltillo (Coahuila), as well as in the mountains ringing the city of Monterrey (Nuevo Leon). MtDNA sequences also suggest a close relationship between alterna and leonis. Additional genetic studies, particularly involving material from areas where the ranges of alterna and leonis converge, should prove helpful in unraveling the evolutionary history of these snakes. 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.  

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. However, to our knowledge, there are no living specimens from Mexico in any collection. 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 (including Panther Canyon), Christmas Mountains, Black Gap, W of Alpine, and Davis Mountains.