Black-necked Gartersnake – Tucson Herpetological Society

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Black-necked Gartersnake (Thamnophis cyrtopsis)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2141″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Black-necked Gartersnakes, Dragoon Mtns, 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=”2617″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Black-necked Gartersnake eating young Sonoran Desert Toad. Photo by Erik Enderson[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2618″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Black-necked Gartersnake eating Chiricahua Leopard Frog. Photo by Erik Enderson[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2619″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Black-necked Gartersnake, Rancho El Aribabi, Sonora, MX. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2620″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Black-necked Gartersnake, Rancho El Aribabi, Sonora, MX. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2621″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Black-necked Gartersnake, Rio Cocospera, Sonora. Photo by Jim Rorabaugh[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2622″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Black-necked Gartersnakes, Dragoon Mountains, AZ. Photo by Jim Rorabaugh[/vc_column_text][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2623″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Black-necked Gartersnake basking, Dragoon Mtns. Photo by Jim Rorabaugh[/vc_column_text][/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 Black-necked Gartersnake (Thamnophis cyrtopsis) is a moderate-sized (< 1144 mm total length [TL], but most are < 700 mm TL) striped snake often common in and near perennial and ephemeral waters in the 100-Mile Circle. The dorsum is dark brown to dark gray with a yellow to orange mid-dorsal stripe on the neck, body, and tail. A white to slightly yellow or cream lateral stripe is present on each side on scale rows two and three. The area between the lateral stripes and the ventral scales is lighter in color than the dark fields between the lateral and mid-dorsal stripes. Between the light stripes, and below the lateral stripes are often alternating rows of small dark spots that are most prominent anteriorly on the body. The top of the head is frequently gray and strongly contrasting with the colors on the body, but some individuals have gray brown or dark brown atop the head. A dark blotch lies on either side of the neck and they are usually separated from each other by the mid-dorsal light stripe. The supralabials are mostly white to yellowish with black seams. The venter is unmarked and cream to greenish. The dorsal scales are keeled and in 19 (rarely to 21) rows at mid-body. The anal plate is undivided, and typically there are eight (7-10) supralabials on each side. The head is not or only slightly differentiated from the neck (Degenhardt et al. 1996, Rossman et al. 1996, Ernst and Ernst 2003).

In the 100-Mile Circle, the Black-necked Gartersnake most closely resembles the Mexican and Checkered gartersnakes (T. eques and T. marcianus, respectively). The most conspicuous difference is the placement of the lateral stripes on the anterior portion of the body. On the Mexican Gartersnake they lie on the 3^rd and 4^th scale rows. On the Checkered Gartersnake, they are on the 3^rd scale row. Three subspecies of the Black-necked Gartersnake are recognized. Only T. c. cyrtopsis occurs in Arizona and the 100-Mile Circle.

In the 100-Mile Circle, the Black-necked Gartersnake is primarily a species of canyon and bajada ephemeral and perennial streams, ciénegas, and cattle tanks in Sonoran and Chihuahuan desertscrub, Plains and semi-desert grassland, oak and pine-oak woodland, and (rarely) mixed conifer forest. It avoids valley bottoms and major rivers where it is replaced by the Checkered and (historically) Mexican gartersnakes. No confirmed records are known for the San Pedro River mainstem or the Gila River in Arizona, although a few records are known for the Santa Cruz River. It has not been found on Cienega Creek, except at the Narrows on the National Conservation Area and in 1985 on the County Preserve (Rosen and Caldwell 2004). However, it is commonly encountered in montane canyons in virtually all of the sky islands and mountains to the east, north, south, and southwest of Tucson, from the Baboquivaris east to the Peloncillos, and north to the Pinals, Superstitions, and Sierra Anchas. In Sonora it has been found from the Río Altar near Altar and Rancho La Bachata (~45 km west-northwest of Caborca) east into Chihuahua. In the Circle it has been found from about 580-2407 m, but most are observed at < 1680 (HerpNet, MABA database). It occurs to near sea level on the coast of Sonora. The species occurs from southeastern Utah and southern Colorado south through Texas, New Mexico, and central and southern Arizona to Guatemala (Rossman et al. 1996).

The Black-necked Gartersnake occurs as an apparently isolated population in the northwestern Ajo Mountains at Organ Pipe Cactus National Monument. It has also been collected on Highway 86 at the northern end of the Quinlan Mountains in areas with little or no obvious surface water. In 1966, it was collected seven miles west of the Three Points Junction on Highway 86 (UAZ 26521), where currently only an ephemeral impoundment in Sonoran desertscrub occurs. I found a T. cyrtopsis on Highway 86 west of Sells on the Tohono O’odham Nation in the 1970s, with no apparent surface water nearby. Even in the heart of its range, this species is sometimes found up to a kilometer from water.

At Burro and Francis creeks in Mohave County, Black-necked Gartersnake local distribution, habitat use, and behavior changed seasonally. In dry periods, snakes congregated around remaining pools where they mostly employed a sit and wait strategy for capturing prey. In wetter times, when streams were flowing, the gartersnakes spread out, using riffles and runs to a greater degree. At that time, they also were more active foragers, moving along banks and in the water as they searched for prey (Jones 1990).

This is mostly a diurnal snake, but it can sometimes be found active at night as well. In the Circle, it has been collected every month of the year except February, but most are found March-October. This species can be abundant, and several may be seen around a water body in a short period of time. In Mohave County, it spends periods of inactivity in rodent burrows, crevices in stream banks and rocks, and in flood debris piles in the floodplain (Jones 1990).

Black-necked Gartersnakes feed upon a wide variety of anurans and their tadpoles, even species with potent skin toxins such as the Sonoran Desert Toad (Incilius alvarius). But they have also been known to take fish (alive or dead), earthworms, a skink, salamanders, a sparrow, and crustaceans (Enderson and Bezy 2002, see review in Ernst and Ernst 2003). Newborn snakes on Burro and Francis creeks, Mohave County, ate mostly fish, tadpoles, and earthworms, whereas adults and subadults ate mostly metamorphosed anurans (mostly Lowland Leopard Frogs, Lithobates yavapaiensis, Jones 1990). These snakes rarely dive, but rather forage on banks and at or near the water’s surface.

Courtship and mating occurs primarily from March to May, but possibly also in the fall, and females give birth to 3-24 young (mean = 8.4) from June through August (Goldberg 1998, Ernst and Ernst 2003). The smallest sexually mature males and females were 338 and 395 mm SVL, respectively (Sabath and Worthington 1959, Goldberg 1998). Neonates are 145-281 mm TL (Ernst and Ernst 2003).

With a valid Arizona hunting license, four Black-necked Gartersnakes may be taken per year or held in possession, alive or dead, except in protected areas such as National Park Service units. The Black-necked Gartersnake is listed as a species of least concern on the 2014 IUCN Red List; however, as a species dependent upon water, it is potentially threatened by water diversions, ground water pumping, pollution, and climate change. In the desert Southwest, most surface waters have been altered in some way, and many have been diminished or dewatered. That said, Black-necked Gartersnakes are still well-represented within the 100-Mile Circle and Arizona. It has likely benefited from creation of cattle tanks. Unlike the Mexican Gartersnake, which has been the victim of predation by introduced species, the Black-necked Gartersnake is much less affected by American Bullfrogs, sportfish, and other introduced species, mainly because it occurs in streams and canyons where introduced species tend not to thrive.

Black-necked Gartersnake (Thamnophis cyrtopsis)

Description

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