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An Annotated Checklist of the Snakes of Atascosa County, Texas

By

Tom Lott




This checklist is based on my almost fifty years of experience-the last twenty-five of those as a resident--with the snakes of Atascosa County. The notes attached to the species list consist of my impressions of individual species' general distribution and abundance.

Atascosa County, Texas includes an area of 1,235.7 square miles and is generally tilted-like most of the state-toward the Gulf coast. It ranges from 725 to 241 feet in elevation above mean sea level. Its principal drainage system is the Atascosa River, a largely permanent flowing watercourse, which runs from the northwestern tip of the county to its southeastern edge. The growing season is 282 days. The mean annual rainfall is 29.0 inches (up from 27.8 inches in 1993). The mean January low temperature is 39° F; the mean July maximum temperature is 95.9° F (down from 97° F in 1993).

The distribution of the snakes of Atascosa County may be best understood in terms of the vegetative habitats to be found within its boundaries. Two major habitats occur within the county: a sandy Post Oak Belt zone-the "Sand Hills" or the "Blackjacks"--in the northern portion and an extensive area of Tamaulipan thornscrub-the "Brush Country"-in the south. Of the two habitats, the Post Oak Belt is the more complex, since great areas of its original forest and savanna have been cleared for agricultural purposes for more than two-hundred years. In most of these areas, in the absence of continuous cultivation or even in the presence of continuous grazing, the original forest species have been replaced by more invasive and faster growing thornscrub species (especially mesquite and prickly pear cactus). Such areas, formerly known ecologically as "disclimaxes," are herein referred to as "second growth" and may harbor snake species that are more characteristic of the Brush Country than would have been the case had the original habitat remained.

There is also substantial historical evidence that the Brush Country we see today was once considerably more prairie-like, featuring much more extensive grasslands. With the development of the cattle industry subsequent to the Civil War and its concomitant overgrazing, the south Texas grasslands were devastated and rapidly replaced in most areas with the familiar thornscrub thickets. Consequently, many prairie/grassland species that were presumably once more widely distributed in south Texas are now relegated to spotty, relictual populations.

The scientific and common names used in this checklist do not necessarily conform to either of the two "standard" herpetological lists but, instead, reflect the author's personal preferences in favor of stability and conservative taxonomic practice.


NON-VENOMOUS SPECIES


South Texas Blind Snake (Leptotyphlops dulcis rubellum) - This tiny subterranean-dwelling snake is common throughout the county in all major habitats.

Texas Glossy Snake (Arizona elegans arenicola) - Common throughout the county in sandy situations.

Eastern Racer (Coluber constrictor) - Rare. Known from Atascosa County only as a literature record. This snake is occasionally encountered around the Choke Canyon Reservoir of adjacent McMullen and Live Oak counties, thus it is to be expected in similarly riparian habitats in Atascosa County. The subspecies occurring in the area is generally conceded to be the Eastern Yellow-bellied Racer (Coluber c. flaviventris), although a juvenile specimen observed in northern McMullen County clearly displayed the characteristic dorsal pattern of the Mexican Racer (C. c. oaxaca), perhaps an indication that these two races intergrade in this area.

Texas Indigo Snake (Drymarchon melanurus erebennus) - This large snake is fairly common in the brushlands of southern Atascosa County. Although it occurs in live-oak savannas in deep south Texas, I have never encountered it in the oak woodlands of the northern part of the county. Texas law prohibits the harassment, collection and/or intentional destruction of this species without a permit.

Eastern Hognose Snake (Heterodon platirhinos)- Fairly common in the sandy northern portions of the county, even in second growth habitats. Apparently absent from the brush country although this species has a tendency to follow the more forested habitats associated with watercourses into less hospitable areas.

Texas Night Snake (Hypsiglena torquata jani) - Surprisingly uncommon in the county, it is likely completely absent from the Post Oak Belt.

Desert King Snake (Lampropeltis getula splendida) - Apparently absent from primary forest zones, this species is fairly common in the brush country to the south.

Mexican Milk Snake (Lampropeltis triangulum annulata) - Although it is rare in second growth zones to the north, and absent from the oak forests, it is fairly common in the brushlands.

Western Coachwhip (Masticophis flagellum testaceus) - Occurs throughout the county, with specimens from the brush country tending to be somewhat larger than those from the forested areas.

Schott's Whipsnake (Masticophis schotti) - A quintessential brush country snake, I have been surprised on several occasions to find it within the northern oak forest zone.

Blotched Water Snake (Nerodia erythrogaster transversa) - Much less common than the Diamondback Water Snake, it is more likely to be restricted to the immediate vicinity of permanent water.

Diamondback Water Snake (Nerodia rhombifer) - Common near water throughout the county, this snake even manages to establish populations in larger, more permanent cattle tanks.

Rough Green Snake (Opheodrys aestivus) - Fairly common and generally distributed in the Post Oak forests of the north, but it is restricted to the environs of watercourses in the brush country.

Southwestern Rat Snake (Pantherophis guttatus meahllmorum) - Rare or absent from the Post Oak woodlands, although it is present in second growth in such areas. Common in the brushlands of the south.

Texas Rat Snake (Pantherophis obsoletus lindheimeri) - Generally distributed in forested areas, in the brush country it is typically found only along streams.

Bull Snake (Pituophis catenifer sayi) - Rare or absent in the climax forests of the Post Oak Belt, but occurs in second growth areas and is fairly common in the brush country.

Longnose Snake (Rhinocheilus lecontei) - Most abundant in the brush country, this colorful snake also occurs in second growth areas within the Post Oak Belt.

Texas Patchnose Snake (Salvadora grahamiae lineata) - Occurs commonly throughout the county but is less abundant in the forested areas.

Texas Brown Snake (Storeria dekayi texana) - Generally distributed within the Post Oak Belt and follows watercourses into the brushlands.

Flat-headed Snake (Tantilla gracilis) - Probably occurs countywide, but is most abundant in the sandy oak forests of the northern part of the county.

Plains Black-headed Snake (Tantilla nigriceps) - Rare or absent from the oak forests, but common in second growth and the brush country.

Checkered Garter Snake (Thamnophis marcianus) - Abundant throughout the county-often phenomenally so after rainfall-this species is slightly less common in forest habitats.

Western Ribbon Snake (Thamnophis proximus) - Common near water throughout the county. Much more restricted to the vicinity of water than the Checkered Garter Snake.

Eastern Garter Snake (Thamnophis sirtalis) - While this is a very common species of the eastern US, the presence of this snake in Atascosa County is suggested by only a single literature record (Dixon, 2000). If present at all, it appears that it could persist in the riparian areas of the southeastern part of the county.

* Lined Snake (Tropidoclonion lineatum) - After two specimens were disgorged by a coral snake collected in the southern portion of the county, several others were road collected in the same general area. This species' spotty distribution is likely due to its being a relict of the once widespread grassland habitat in south Texas.

* Rough Earth Snake (Virginia striatula) - Fairly common in the sandy forests of the northern part of the county, it persists as well in second growth habitats and also in the wetter portions of the brush country.

(*) = These species have not yet been formally reported from the county and their inclusion here is based solely on my personal observations.


VENOMOUS SPECIES


Broad-banded Copperhead (Agkistrodon contortrix laticinctus) - Abundant in the sandy northern forested zones of the county and tends to at least persist in second growth areas. Apparently absent from the thornscrub brushlands of the southern portion of the county, although they may follow riparian zones associated with streams into this otherwise inhospitable habitat.

Western Cottonmouth (Agkistrodon piscivorus leucostoma) - Uncommon. This is a semi-aquatic snake that is generally restricted to riparian areas along permanent watercourses. Occasionally, however, this species can become established around larger permanently filled cattle tanks, suggesting that they will wander across drier land to reach new water sources.

Western Diamondback Rattlesnake (Crotalus atrox) - Abundant in the brush country of the southern portion of the county. Rare or absent in forested zones of the Post Oak Belt but rapidly colonizes such areas when they are cleared and thornscrub species (especially mesquite and prickly pear cactus) are subsequently allowed to invade.

Texas Coral Snake (Micrurus tener) - Relatively common throughout the county in all major habitats.


HYPOTHETICAL SPECIES


These species are considered likely to be eventually found in Atascosa County based on their occurrence in similar habitats in adjacent counties. Special effort should be made to report specimens of these forms found in the county to the author.

Mexican Hook-nosed Snake (Ficimia streckeri) - Likely occurs in the brushlands of the extreme southern portion of the county. Specimens have been taken in adjacent parts of Live Oak and McMullen counties.

Mexican Hognose Snake (Heterodon kennerlyi) - The distribution of this snake is spotty throughout south Texas. Specimens are known from adjacent McMullen and LaSalle counties to the south and Bexar County to the north. Possibly occurs in the brushlands of the extreme southern portion of Atascosa County. Some authors consider this species to be merely a geographic race of the Western Hognose Snake (Heterodon nasicus) of the Great Plains, and there is very little obvious difference between the two.

Graham's Crayfish Snake (Regina grahami) - Given that this snake is found near most permanent streams in adjacent Bexar County, it is almost certainly to be found in similar habitats in Atascosa County.

Southern Texas Ground Snake (Sonora semiannulata taylori) - Another relict grassland species with a correspondingly spotty south Texas distribution, it is well known from similar such areas of adjacent Bexar County.


PRINT REFERENCES


Brown, B. C. 1950. An annotated check list of the reptiles and amphibians of Texas. Waco: Baylor University Studies.

Conant, R and J. T. Collins. 1998. A field guide to the reptiles and amphibians: Eastern and central North America. 3rd edition (expanded) Boston: Houghton Mifflin Co.

Dixon, J. R. 2000. Amphibians and reptiles of Texas. 2nd Ed. W. L. Moody, Jr., Nat. Hist. Ser. 25. College Station: Texas A&M University Press.

Dixon, J. R. and J. E. Werler. 2005. Texas Snakes: A Field Guide. Austin: University of Texas Press.

Tennant, A. 1984. The snakes of Texas. Austin: Texas Monthly Press.

Vermersch, T.G. and R.E. Kuntz. 1986. Snakes of South Central Texas. Eakin Press, Austin, Texas.

Werler, J. E. and J. R. Dixon. 2000. Texas Snakes: Identification, Distribution, and Natural History. Austin: University of Texas Press

Wright, A. H., and A. A. Wright. 1957. Handbook of snakes of the United States and Canada. Ithaca, N. Y.: Comstock Publishing Co.


ON-LINE REFERENCES


Texas Cooperative Wildlife Collection, Division of Amphibians and Reptiles


Date submitted 02/10/08






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