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| NAS - Nonindigenous Aquatic Species |
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Common Name: Tessellated Watersnake
Synonyms and Other Names: dice snake
Taxonomy: available through 
Identification: The tessellated watersnake has strongly keeled dorsal scales, numbering 19 midbody rows, and a divided anal scale (Steward, 1971; Street, 1979; Leviton et al., 1992). The head may appear narrow and elongate (Arnold and Burton, 1978). Dorsal coloration varies from brown, gray-green, to olive, sometimes with a reddish tinge, with four or more longitudinal rows of dark brown or black squares or blotches; the blotches may unite across the dorsum to form crossbars (Arnold and Burton, 1978; Street, 1979; Trutnau, 1986; Arnold and Ovenden, 2002). The neck often has a distinct black chevron (Steward, 1971; Street, 1979; Arnold and Ovenden, 2002). Some individuals can have no markings or be completely black (Steward, 1971; Arnold and Burton, 1978; Street; 1979; Arnold and Ovenden, 2002). Natrix tessellata has 160-197 ventral scales, and 48-86 subcaudal scales (Leviton et al., 1992). The length of this species is 610-1,371 mm (24-54 in) (Steward, 1971). This species may be confused with indigenous water snakes (Nerodia) and garter snakes (Thamnophis); however, the garter snakes can at least be distinguished from N. tessellata because almost all Thamnophis have a single, undivided anal scale (Conant and Collins, 1998). Natrix tessellata has been illustrated by a variety of authors (Steward, 1971; Hvass, 1972; Arnold and Burton, 1978; Street, 1979; Trutnau, 1986; Mattison, 1987, 1992; Mehrtens, 1987; Leviton et al., 1992; Zhao and Adler, 1993; Saint-Girons, 1994; Schleich et al., 1996; Arnold and Ovenden, 2002).
Size: 610 - 1,371 mm total body length
Native Range: Natrix tessellata has a very broad distribution in central and southeastern, continental Europe (including Albania, Austria, Czech Republic, Hungary, Italy, Germany, Croatia, Greece, Romania, Switzerland, the other Balkans) to central Asia as far east as western China, south through Turkey, across southwestern Asia to Afghanistan and Pakistan, the Near East, including Iran, Iraq, Israel, Jordan, and into the Nile Delta of Egypt, Africa (Minton, 1966; Steward, 1971; Hvass, 1972; Arnold and Burton, 1978; Street, 1979; Trutnau, 1986; Mehrtens, 1987; Leviton et al., 1992; Zhao and Adler, 1993; Schleich et al., 1996; Arnold and Ovenden, 2002). An isolated population may occur in Yemen (Leviton et al., 1992), and in Europe there is an isolated population in the Rhine Valley, Germany (Arnold and Ovenden, 2002). European populations along the River Elbe are now extinct (Arnold and Ovenden, 2002).
Nonindigenous Occurrences: In May 1982, a juvenile N. tessellata (USNMFS 115808) was found in a warehouse near the Norfolk Naval Base, Norfolk, Virginia, U.S. (Mitchell, 1994).
A nonindigenous population of N. tessellata was established in Yorkshire, Great Britain, in the 1970s (Arnold, 1995). Populations in Switzerland, north of the Alps, are probably introduced (Arnold and Ovenden, 2002).
Means of Introduction: This single specimen was a waif introduced by overseas freight shipments (Mitchell, 1994).
Status: Not established in the U.S. The only currently established, nonindigenous, European populations are north of the Alps in Switzerland (Arnold and Ovenden, 2002).
Impact of Introduction: None in the U.S. Given their strong similarity in habits and diet to indigenous Nerodia and Thamnophis in the U.S. an established population could have a negative impact through competition. Moreover, N. tessellata could negatively impact indigenous fish and amphibians by causing them to undergo increased predation pressure.
The impact of established nonindigenous European populations is unknown.
Remarks: The taxonomy of N. tessellata has been summarized by Malnate (1960), Rossman and Eberle (1977), and Leviton et al. (1992). The tessellated water snake is an aquatic snake (except when basking on land) that feeds primarily on fish and amphibians (Steward, 1971; Arnold and Burton, 1978; Street, 1979; Trutnau, 1986; Arnold and Ovenden, 2002). They can be found in or near almost any aquatic habitat (Arnold and Burton, 1978; Street, 1979; Leviton et al., 1992; Arnold and Ovenden, 2002). Tessellated water snakes may bask in branches above water (Trutnau, 1986). When threatened, N. tessellata can feign death to deter a predator (Saint-Girons, 1994). Female tessellated watersnakes lay their flexible-shelled eggs on land in a moist sheltered environment such as loose soil beneath objects, rotting vegetation, anthropogenic refuse, and crevices of stone walls (Steward, 1971; Street, 1979; Arnold and Ovenden, 2002).
In Europe, N. tessellata are commonly kept by snake hobbyists (Trutnau, 1986; Mattison, 1987, 1992; Arnold, 1995).
References
Arnold, E. N., and J. A. Burton. 1978. A Field Guide to the Reptiles and Amphibians of Britain and Europe. Collins, London. 272 pp.
Arnold, E. N., and D.W. Ovenden. 2002. Reptiles and Amphibians of Europe. Princeton University Press, Princeton. 288 pp.
Arnold, H. R. 1995. Atlas of amphibians and reptiles in Britain. Institute of Terrestrial Ecology Research Publication (London) (10):1-40.
Conant, R., and J. T. Collins. 1998. A Field Guide to Reptiles & Amphibians. Eastern and Central North America. Third Edition, Expanded. Houghton Mifflin Company, Boston. 616 pp.
Hvass, H. 1972. Reptiles and Amphibians in Colour. First English Edition. Blandford Press, London. 153 pp.
Leviton, A. E., S. C. Anderson, K. Adler, and S. A. Minton, [Jr.] 1992. Handbook to Middle East Amphibians and Reptiles. Contributions to Herpetology 8. Society for the Study of Amphibians and Reptiles, Oxford, Ohio. 252 pp.
Malnate, E. V. 1960. Systematic division and evolution of the colubrid snake genus Natrix, with comments on the subfamily Natricinae. Proceedings of the Academy of Natural Sciences of Philadelphia 112:41-71.
Mattison, C. 1987. The Care of Amphibians and Reptiles in Captivity. Revised Edition. Blandford Press, London. 317 pp.
Mattison, C. 1992. A-Z of Snake Keeping. First American Edition. Sterling Publishing Co., Inc., New York. 143 pp.
Mehrtens, J. M. 1987. Living Snakes of the World in Color. Sterling Publishing Co., Inc., New York. 480 pp.
Minton, S. A., Jr. 1966. A contribution to the herpetology of West Pakistan. Bulletin of the American Museum of Natural History 134(2):27-184.
Mitchell, J. C. 1994. The Reptiles of Virginia. Smithsonian Institution Press, Washington and London. 352 pp.
Rossman, D. A., and W. G. Eberle. 1977. Partition of the genus Natrix, with preliminary observations on evolutionary trends in natricine snakes. Herpetologica 33(1):34-43.
Saint-Girons, M.-C. 1994. Postures & behavior: Defense or intimidation. Pp. 162-171. In: R. Bauchot (editor). Snakes. A Natural History. English Translation [Edition]. Sterling Publishing Co., Inc., New York. 220 pp.
Schleich, H. H., W. Kästle, and K. Kabisch. 1996. Amphibians and Reptiles of North Africa. Koeltz Scientific Books, Koenigstein. 630 pp.
Steward, J. W. 1971. The Snakes of Europe. First American Edition. Associated University Presses, Inc., Cranbury, New Jersey. 238 pp. Street, D. 1979. The Reptiles of Northern and Central Europe. B. T. Batsford Ltd., London. 268 pp.
Trutnau, L. 1986. Nonvenomous Snakes. First English Language Edition. Barron's Educational Series, Inc., Woodbury, New York. 191 pp.
Zhao, Er-mi, and K. Adler. 1993. Herpetology of China. Contributions to Herpetology 10. Society for the Study of Amphibians and Reptiles, Oxford, Ohio. 522 pp.
Other Resources:
Author: Louis A. Somma
Revision Date: 11/24/2003 Citation for this information:
Louis A. Somma. 2009. Natrix tessellata. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1194> Revision Date: 11/24/2003
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