Checkered Gartersnake (Thamnophis marcianus)

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Checkered Gartersnake (Thamnophis marcianus)


The Checkered Gartersnake (Thamnophis marcianus) is a moderately long gartersnake (<1088 mm total length, < 988 mm SVL) that in our area is characterized by a yellow or orange mid-dorsal stripe and a light lateral stripe on each side on the 3rd scale row anteriorly. Between the mid-dorsal and lateral stripes are black, squarish spots in an alternating checkerboard pattern on a yellowish-brown, light brown or olive background.  A cream or yellow crescent marks the rear lateral aspect of each side of the head, which are followed by a dark blotch on each side of the neck. The supralabials are marked with light and dark vertical slashes, and usually there is a small light spot atop the head and posterior to the eyes along the margin of the parietal scales. The ventral surface is cream-colored to light gray and virtually without any markings.  The tongue is red and black, and the pupil is round.

Photo by Jim Rorabaugh

Checkered Gartersnake, Cochise Cnty, AZ. Photo by Jim Rorabaugh

The keeled dorsal scales typically number 19 (rarely as many as 23) at mid-body, and the anal plate is undivided. Supralabials number 8 (rarely 7 or 9), infralabials number 10.  There is one loreal scale on each side. The largest males are smaller than the largest females, but the male tail is proportionally longer and males average greater numbers of subcaudal scales than females.  Juveniles resemble small adults and are 123-279 mm total length at birth.

The above description applies to snakes in our area (T. m. marcianus); the other subspecies (T. m. bovalii, T. m. praeocularis), which occur in southern Mexico and Central America, possess a different suite of characters.

The Checkered Gartersnake resembles the other three gartersnake species in our area: the Black-necked, Mexican, and Terrestrial Gartersnakes.  The best character for distinguishing among them is the placement of the lateral light stripe near the head.  It is located on the 3rd and 4th scale rows on the Mexican Gartersnake and the 2nd and 3rd scale rows on the Black-necked and Terrestrial Gartersnakes (3rd scale row on the Checkered Gartersnake).

In the 100-Mile Circle, the Checkered Gartersnake is primarily a species of river valleys.  It is found in the Altar and Avra Valleys, the Santa Cruz River from Tucson south to at least Rio Rico, Sonoita Creek, Las Cienegas, the upper and lower reaches of the San Pedro River, the Sulphur Springs Valley from Bonita south to Whitewater Draw, the San Bernardino Valley, and the San Simon Valley.  It also occurs along the Gila and Salt Rivers and associated agricultural lands.  There are a few records from the San Rafael Valley (Jones et al. 2014), and a single record for Aravaipa Creek near its confluence with the San Pedro River. In Sonora, the only records for Checkered Gartersnake in the 100-Mile Circle are from the Cananea area and the Río San Rafael, a western tributary of the San Pedro.  A collection near Agua Prieta is just outside of the Circle.

Photo by Young Cage

South of the Gila River there are no records for this species between the Avra Valley and the Colorado River.  It occurs along the Gila and in associated agricultural lands as far downstream as Painted Rock Reservoir, but there are no records between there and Fortuna Pond (on the Gila about 10 km E of the Colorado confluence).  It likely occurred throughout the lower Gila River historically when flow in the river was more dependable, and may still occur in agriculture of the lower Gila Valley.  Throughout its range, the Checkered Gartersnake occurs from the southwestern and south-central USA south through portions of Mexico to Nicaragua.

In the Circle, it is generally absent from the mountains, although there are records from the Southwest Research Station in the Chiricahua Mountains, the northeastern flank of the Huachuca Mountains, and on the lower, southern slopes (1350 m elevation) of the Whetstone Mountains.  It occurs in lower Sabino Canyon at the base of the Catalina Mountains, as well.

The Checkered Gartersnake is usually found at or near water, which may take the form of rivers, lakes, cattle tanks, agricultural areas, canals, and ditches.  Both ephemeral and perennial waters are used, although this snake is most likely to be abundant in perennial water.  Checkered Gartersnakes are good at finding new sources of water, such as isolated cattle tanks, and are sometimes encountered a kilometer or more from water.  Wetlands at which they are found occur in Sonoran and Chihuahuan desertscrub, semi-desert grassland, and Plains grassland.  The species also occurs rarely into the lower reaches of oak and pine-oak woodland. Elevational occurrence in the 100-Mile Circle is about 322 m at the Gila River to 1643 m at the Southwest Research Station.

Unlike the Mexican Gartersnake, the Checkered Gartersnake is proficient at coexisting with non-native fishes, American Bullfrogs, Rio Grande Leopard Frogs, crayfish, and a variety of aquatic turtles.  Rosen and Schwalbe (2002) suggest that Checkered Gartersnakes, especially the juveniles that are particularly susceptible to predation, are more terrestrial than Mexican Gartersnakes, putting them out of the danger zone where non-native aquatic predators are most common. On the lower Colorado River, where Checkered Gartersnakes occur from just north of Imperial Dam south to the Ciénega de Santa Clara, Sonora, the species is almost always associated with thick emergent cover that likely shields them from predators (pers. observation).

There are Checkered Gartersnake records in the 100-Mile Circle from every month of the year except February, although most snakes are found from April through October. This species is probably active on warm days through winter at low elevations, such as in the Phoenix area. It is active by day or at night, with nocturnal activity becoming more common in the heat of summer.

Photo by Jim Rorabaugh

Checkered Gartersnake, Cochise Cnty, AZ. Photo by Jim Rorabaugh

In a captive population of Checkered Gartersnakes from Graham County, courtship and mating took place within two days of emergence from hibernation (Ford and Cobb 1992).  Courtship was observed in the wild at Roper Lake State Park, Graham County, on March 27 (Seigel et al. 2000).  Perry-Richardson et al. (1990) described courtship in captive snakes from southern Arizona. Copulation in those captive snakes lasted 5-6 minutes.  They found that cloacal alignment is accomplished by aligning the tail tips, so snakes with truncated tails (common in populations with elevated levels of predation) may have difficulty accomplishing proper alignment.  Adults are about >515 and >458 mm SVL (females and males, respectively) in southeastern Arizona (Seigel et al. 2000), and females typically outnumber males. Throughout the range of T. m. marcianus, litters of 3-35 snakes are born from mid-May into October.  Two litters may be produced in favorable years. At Roper Lake State Park, mean clutch size was 14.1 (for 20 clutches) and births and gravid females occurred almost exclusively from late May through the end of June (Seigel et al. 2000).  Parthenogenesis has been documented in a captive, virgin female. That female produced five litters that included reproductively viable males (Reynolds et al. 2012).  How often parthenogenesis occurs in wild Checkered Gartersnakes is unknown. Females are also capable of storing sperm.

The diet of the Checkered Gartersnake is varied, and probably opportunistic.  These snakes actively search for prey with sight and smell.  A wide variety of frogs, toads, spadefoots and their larvae are taken, as well as salamanders, snakes, lizards, fish, earthworms, slugs, and crayfish (see review in Ernst and Ernst 2003). In the population at Roper Lake State Park, Checkered Gartersnakes were found to consume small American Bullfrogs and their tadpoles, and earthworms.  Juveniles ate a higher percentage of earthworms than adults (Seigel et al. 2000).  In captivity, Checkered Gartersnakes have also taken raw horse meat and consumed their own kind (Ernst and Ernst 2003).

Checkered Gartersnakes may bite when first captured, but usually tame down rapidly and do well in captivity.  However, even long-term captives may smear their handlers with musk and feces.

The Checkered Gartersnake is a species of least concern on the 2013 IUCN Red List. With a valid Arizona hunting license, four may be captured per year or held in possession, live or dead.  This species is eliminated by urbanization and activities that drain or otherwise destroy wetlands; however, it likely has benefited from construction of cattle tanks and development of agriculture.  In agricultural areas, it probably does better in areas of tree crops (e.g. citrus, pecans, date palms) as opposed to seasonal row crops that are plowed up on a regular basis.

Suggested Reading:

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.

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.

Ford, N.B., and V. Cobb. 1992. Timing of courtship in two Colubrid snakes of the southern United States. Copeia 1992(2):573-577.

Jones, T.R., R.J. Timmons, and J.C. Rorabaugh. 2014. Geographic Distribution. Thamnophis marcianus (Checkered Gartersnake). Herpetological Review 45(4):666.

Perry-Richardson, J.J., C.W. Schofield, and N.B. Ford. 1990. Courtship of the garter snake, Thamnophis marcianus, with a description of female behavior for coitus interruption. Journal of Herpetology 24:76-78.

Reynolds, R.G., W. Booth, G.W. Schuett, B.M. Fitzpatrick, and G.M. Burghardt. 2012. Successive virgin births of viable male progeny in the checkered gartersnake, Thamnophis marcianus. Biological Journal of the Linnean Society 107(3):566-572.

Rosen, P.C., and C.R. Schwalbe. 2002. Widespread effects of introduced species on reptiles and amphibians in the Sonoran Desert Region. Pages 220-240 in B. Tellman (ed.), Invasive Exotic Species in the Sonoran Region. University of Arizona Press and the Arizona-Sonora Desert Museum, Tucson.

Rossman, D.A., N.B. Ford, and R.A. Seigel. 1996. The Garter Snakes, Evolution and Ecology. University of Oklahoma Press, Norman.

Seigel, R.A., N.B. Ford, and L.A. Mahrt. 2000.  Ecology of an aquatic snake (Thamnophis marcianus) in a desert environment: implications of early timing of birth and geographic variation in reproduction. American Midland Naturalist 143:453-462.

Author: Jim Rorabaugh

For additional information on this species, please see the following volume and pages in the Sonoran Herpetologist: 2004 Sep:82-86.