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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: Cottonmouth

Synonyms and Other Names: water moccasin, swamp moccasin, black moccasin, gaper

Taxonomy: available through www.itis.gov

Identification: Agksitrodon piscivorus is a large, heavy-bodied species of pit viper snake (Gloyd and Conant, 1990; Conant and Collins, 1998). The back (dorsum) of a Cottonmouth varies in color from olive to brown, or black, with broad crossbands that vary from distinct to obscure, or absent (Gloyd and Conant, 1990; Conant and Collins, 1998). The pattern darkens with age so adults retain only a hint of the former banding or are a uniform black. This specie’s scales are keeled and they have eyes with a catlike vertical slit. The eyes are camouflaged by a broad, dark, facial stripe and the tip of the snout has two vertical dark lines. The head is thick and distinctly broader than the neck (diamond shape), and when viewed from above, the eyes cannot be seen. The top of head in front of the eyes is covered with large plate-like scales with deep facial pits between the nostril and the eyes (Florida Museum of Natural History, 2018).  Young Cottonmouths are strongly patterned and have a yellow tail (Behler and King, 1979; Gloyd and Conant, 1990; Lamar, 1997; Conant and Collins, 1998). When threatened, the cottonmouth may respond by coiling its body and opening its mouth as though ready to bite.  The exposed white interior of the mouth is what gave rise to the common name, 'cottonmouth.' Given the chance, the cottonmouth usually will retreat. This open mouth threat display has led to the widespread belief that cottonmouths are aggressive snakes (Florida Museum of Natural History, 2018).

There are three subspecies (races):  A. piscivorus conanti Gloyd, 1969, the Florida Cottonmouth; A. piscivorus piscivorus (Lacepède, 1789), the Eastern Cottonmouth; and A. piscivorus leucostoma (Troost, 1836), the Western Cottonmouth.  Typically, A. p. conanti has the most prominent bands and facial markings of the three subspecies but there is much variation within each taxon (Gloyd and Conant, 1990; Conant and Collins, 1998).  In A. p. leucostoma males are more likely to have prominent bands than females (Zaidan, 2001). Identification of individual subspecies is made more difficult by a broad geographic area of intergradation between all three of them (Conant and Collins, 1998).  

Numerous authorities provide illustrations of cottonmouths (Behler, 1999; Phillips et al., 1999; Johnson, 2000; Tennant and Bartlett, 2000; Werler and Dixon, 2000).

Cottonmouths vs. watersnakes

Unlike species of the nonvenomous genus Nerodia (watersnakes), Cottonmouths have a facial, heat-sensing pit between each nostril and eye, which is larger than the nostril.  The eyes of the Cottonmouth are a catlike vertical slit and cannot been seen from the top of the head, while water snakes have round pupils that can be seen from the top of the head.  Additionally, the dorsal portion of the Cottonmouth's chunky heads are distinctly flattened and covered with a few large scales, and they possess a single anal scale; characteristics not found in watersnakes (Conant and Collins, 1998; Powell et al., 1998). Most Cottonmouths stand their ground when approached and may gape their mouths widely, revealing the pale or cottony-white interior in a threat display. Unlike the escape behavior of the nonvenomous watersnake species, (Gloyd and Conant, 1990; Conant and Collins, 1998; Werler and Dixon, 2000). See Florida Museum of Natural History for a comparison of watersnakes and Cottonmouths.

Size: 760- 1892 mm total length (Gloyd and Conant, 1990; Conant and Collins, 1998)

Native Range: The Florida Cottonmouth is distributed in Florida, including the upper Keys, and extreme southeastern Georgia; the Eastern Cottonmouth from southeastern Virginia, the Carolinas, and Georgia; the Western Cottonmouth from eastern Texas, Oklahoma, Kansas (eastern Cherokee County only), Louisiana, Arkansas, southern Missouri, western Tennessee, extreme southern Illinois and Indiana, Mississippi, western Kentucky, and western Alabama (Martof, 1956; Smith, 1961; Webb, 1970; Minton, 1972; Mount, 1975; Stevenson, 1976; Linzey, 1979; Linzey and Clifford, 1981; Lohoefener and Altig, 1983; Moler, 1988; [Sievert] and Sievert, [1988]; Carpenter and Krupa, 1989; Dundee and Rossman, 1989; Lazell, 1989; Gloyd and Conant, 1990; Carmichael and Williams, 1991; Gibbons and Semlitsch, 1991; Collins, 1993; Mitchell, 1994; Palmer and Braswell, 1995; Boundy, 1997; Tennant, 1997; Conant and Collins, 1998; Price, 1998; Tennant et al., 1998; Phillips et al., 1999; Dixon, 2000; Johnson, 2000; King, 2000; Werler and Dixon, 2000). Intergrades between the three subspecies exist in a broad region encompassing Alabama, and parts of Mississippi, Georgia, South Carolina, and the western Florida panhandle (Gloyd and Conant, 1990; Conant and Collins, 1998). Such "intergrades" may represent clinal variation; suggesting problems in officially recognizing the three subspecific taxa.

To date there is no evidence that cottonmouths occur across the Rio Grande River in adjacent Mexico (Smith and Smith, 1993), and disjunct Rio Grande populations in Texas have been extirpated (Gloyd and Conant, 1990; Conant and Collins, 1998).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: These large, venomous pitvipers are semiaquatic snakes that eat a variety of terrestrial and aquatic vertebrates including fish, amphibians, snakes, turtles, baby alligators, mammals, and birds (Wharton, 1969; Dundee and Rossman, 1989; Gloyd and Conant, 1990; Palmer and Braswell, 1995; Conant and Collins, 1998;  Johnson, 2000; Werler and Dixon, 2000; Davis, 2002). The foraging activity of Cottonmouths is both aquatic and terrestrial, and often involves remaining in wait to ambush prey (Wharton, 1969; Gloyd and Conant, 1990; Conant and Collins, 1998; Werler and Dixon, 2000; Andreadis, 2001). Young lure frogs within striking range by wiggling their yellow tails (Wharton, 1960; Lamar, 1997). Females give live birth to 5-11 young in late summer or early fall (Wharton, 1966; Gloyd and Conant, 1990); some females briefly remain with their young to provide some degree of parental care (Wharton, 1960, 1966; reviewed in Somma, 2003).

Means of Introduction: The cottonmouth from Boulder, Colorado, was intentionally introduced "by a farmer to scare away fishermen" (Livo et al., 1998). The Montgomery County, Kansas cottonmouths also were introduced intentionally (Collins, 1993). The specimen from Massachusetts may have been a released pet or escapee (Cardoza et al., 1993). It is not clear if the formerly established colonies of A. piscivorus from Livingston County, Missouri, were introduced or natural (Gloyd and Conant, 1990).

Status: A. piscivorus was never established in Massachusetts. The disjunct population of A. piscivorus in Livingston County, Missouri, was determined extirpated by Johnson (1987). Currently, no natural populations of A. piscivorus in Missouri exist north of the Missouri River (Johnson, 1987, 2000; Gloyd and Conant, 1990). The cottonmouths in Montgomery County, Kansas are extirpated (Collins, 1993). Agkistrodon piscivorus is not established in Colorado (Livo et al., 1998; Hammerson, 1999).

Impact of Introduction: The impact of cottonmouths formerly inhabiting Livingston County, Missouri, remains unknown as it was never determined if they were introduced or indigenous.

Remarks: Another snake was found in the space between the inner and outer hulls of a barge in Winona, Minnesota in 2006 (Cochran 2008). The barge had come from Baton Rouge, Louisiana and likely picked up this hitch hiker from there. The specimen was preserved and is stored at Bell Museum of Natural History (JFBM15215) (Cochran 2008).  This specimen is not included in the NAS database because it was intercepted and was never released.

The taxonomy of A. piscivorus has been reviewed or summarized by several authors (Gloyd and Conant, 1990; Golay et al., 1993; McDiarmid et al., 1999; Boundy et al., 2000).   A variety of authors have reviewed or contributed to the natural history of cottonmouths (Wright and Wright, 1957, 1962; Wharton, 1960, 1966, 1969; Dundee and Rossman, 1989; Ernst and Barbour, 1989; Gibbons and Semlitsch, 1991; Palmer and Braswell, 1995; Conant and Collins, 1998; Johnson, 2000; Werler and Dixon, 2000; and many others cited herein), but the best overall summary is Gloyd and Conant (1990). Scientific and standard English names follow Crother (2008).

Most A. piscivorus stand their ground when approached, unlike the escape behavior of the nonvenomous Nerodia species, and may gape their mouths widely, revealing the pale or cottony-white interior in a threat display (Gloyd and Conant, 1990; Conant and Collins, 1998; Werler and Dixon, 2000).

These carnivorous snakes have the potential to impact indigenous wildlife if introduced out of their indigenous range, and their venom adds a potentially life-threatening presence to the human populace.

References: (click for full references)

Anderson, P. 1965. The Reptiles of Missouri. University of Missouri Press, Columbia, Missouri. 330 pp.

Andreadis, P. T. 2001. Nocturnal behavior of cottonmouths recorded with near-infrared video. Joint Annual Meetings Herpetologists' League, The Society for the Study of Amphibians and Reptiles [Abstracts] (Indianapolis, Indiana) 2001:41.

Ashton, R. E., Jr., and P. S. Ashton. 1981. Handbook of Reptiles and Amphibians of Florida. Part One. The Snakes. Windward Publishing, Inc., Miami. 176 pp.

Behler, J. L. 1999. National Audubon Society First Field Guide. Reptiles. Scholastic, Inc., New York. 160 pp.

Behler, J. L., and F. W. King. 1979. The Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf, Inc., New York. 743 pp.

Boundy, J. 1997. Snakes of Louisiana. Louisiana Department of Wildlife & Fisheries, Baton Rouge. 32 pp.

Boundy, J., J. [A.] Campbell, B. [I.] Crother, and T. Taggart. 2000. Squamata—snakes. Pp. 56-74. In: B. I. Crother (chair), and Committee on Standard English and Scientific Names (editors). Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. Society for the Study of Amphibians and Reptiles Herpetological Circular (29):i-iii, 1-82.

Cardoza, J. E., G. S. Jones, T. W. French, and D. B. Halliwell. 1993. Exotic and Translocated Vertebrates of Massachusetts. Fauna of Massachusetts Series 6. Massachusetts Division of Fisheries and Wildlife, Westborough, Massachusetts. 106 pp.

Carmichael, P., and W. Williams. 1991. Florida's Fabulous Reptiles and Amphibians. World Publications, Tampa. 120 pp.

Carpenter, C. C., and J. J. Krupa. 1989. Oklahoma Herpetology. An Annotated Bibliography. University of Oklahoma Press, Norman. 258 pp.

Collins, J. T. 1993. Amphibians and Reptiles in Kansas. Third Edition, Revised. The University of Kansas, Museum of Natural History, Lawrence. 397 pp.

Cochran, P. A.  2008.  A cottonmouth (Agkistrodon piscivorus) in Minnesota, and historical reports of other pit vipers unexpected in the Upper Midwest.  Northeastern Naturalist 15(3):461-464.

Conant, R. 1958. A Field Guide to Reptiles and Amphibians of the United States and Canada East of the 100th Meridian. Houghton Mifflin Company, Boston. 366 pp.

Conant, R. 1975. A Field Guide to Reptiles and Amphibians of Eastern and Central North America. Houghton Mifflin Company, Boston. 429 pp.

Conant, R. 1997. A Field Guide to the Life and Times of Roger Conant. Selva, Provo, Utah. 498 pp.

Conant, R. 2002. Herp collecting in Florida in 1930. Bulletin of the Chicago Herpetological Society 37(7):117-120.

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.

Crother, B.I. (chair). Committee on Standard and English and Scientific Names. 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. Society for the Study of Amphibians and  Reptiles Herpetological Circular. No. 37. iii + 86p.

Davis, J. B. 2002. Agkistrodon piscivorus (cottonmouth). Predation. Herpetological Review 33(2):136-137.

Dixon, J. R. 2000. Amphibians and Reptiles of Texas. Second Edition. Texas A & M University Press, College Station. 421 pp.

Dundee, H. A., and D. A. Rossman. 1989. The Amphibians and Reptiles of Louisiana. Louisiana State University Press, Baton Rouge and London. 300 pp + unattached erratum.

Ernst, C. H. 1992. Venomous Reptiles of North America. Smithsonian Institution Press, Washington and London. 236 pp.

Ernst, C. H., and R. W. Barbour. 1989. Snakes of Eastern North America. George Mason University Press, Fairfax, Virginia. 282 pp.

Freiberg, M., and J. G. Walls. 1984. The World of Venomous Animals. T.F.H. Publications, Inc., Neptune City, New Jersey. 191 pp.

Gibbons, J. W., and R. D. Semlitsch. 1991. Guide to the Reptiles and Amphibians of the Savannah River Site. The University of Georgia Press, Athens, Georgia, and London. 131 pp.

Gloyd, H. K., and R. Conant. 1990. Snakes of the Agkistrodon Complex. A Monographic Review. Society for the Study of Amphibians and Reptiles, Oxford, Ohio. 614. pp.

Golay, P., H. M. Smith, D. G. Broadley, J. R. Dixon, C. McCarthy, J.-C. Rage, B. Schätti, and M. Toriba. 1993. Endoglyphs and Other Major Venomous Snakes of the World. A Checklist. AZEMIOPS S.A., Herpetological Data Center, Geneva. 478 pp.

Hammerson, G. A. 1999. Amphibians and Reptiles in Colorado. Second Edition. University Press of Colorado, Niwot, Colorado. 484 pp.

Jackson, J. J. 1983. Snakes of the Southeastern United States. Publications Section, Georgia Extension Service, [Athens, Georgia]. 112 pp.

Johnson, T. R. 1987. The Amphibians and Reptiles of Missouri. Missouri Department of Conservation, Conservation Commission of the State of Missouri, Jefferson City. 368 pp.

Johnson, T. R. 2000. The Amphibians and Reptiles of Missouri. Revised and Expanded Second Edition. Missouri Department of Conservation, Conservation Commission of the State of Missouri, Jefferson City. 400 pp.

King, F. W. 2000. Florida Museum of Natural History's Checklist of Florida Amphibians and Reptiles [online]. Florida Museum of Natural History, University of Florida, Gainesville. Available on URL: http://www.flmnh.ufl.edu/herps/FL-GUIDE/Flaherps.htm.

Lamar, W. W. 1997. The World's Most Spectacular Reptiles & Amphibians. World Publications, Tampa. 208 pp.

Lazell, J. D., Jr. 1989. Wildlife of the Florida Keys: A Natural History. Island Press, Washington, D.C. 250 pp.

Linzey, D. W. 1979. Snakes of Alabama. The Strode Publishers, Inc., Huntsville, Alabama. 136 pp.

Linzey, D. W., and M. J. Clifford. 1981. Snakes of Virginia. University Press of Virginia, Charlottesville. 159 pp.

Livo, L. J., G. A. Hammerson, and H. M. Smith. 1998. Summary of amphibians and reptiles introduced into Colorado. Northwestern Naturalist 79(1):1-11.

Lohoefener, R., and R. Altig. 1983. Mississippi herpetology. Mississippi State University Research Center Bulletin (1):i-vi, 1-66.

Martof, B. S. 1956. Amphibians and Reptiles of Georgia. University of Georgia Press, Athens, Georgia. 94 pp.

Martof, B. S., W. M. Palmer, J. R. Bailey, and J. R. Harrison III. 1980. Amphibians and Reptiles of the Carolinas and Virginia. The University of North Carolina Press, Chapel Hill. 264 pp.

McDiarmid, R. W., J. A. Campbell, and T'S. A. Touré. 1999. Snake Species of the World. A Taxonomic and Geographic Reference. Volume 1. The Herpetologists' League, Washington, D.C. 511 pp.

Minton, S. A., Jr. 1972. Amphibians and reptiles of Indiana. Indiana Academy of Science Monograph (3):i-v, 1-346.

Mitchell, J. C. 1994. The Reptiles of Virginia. Smithsonian Institution Press, Washington and London. 352 pp.

Moler, P. 1988. A Checklist of Florida's Amphibians and Reptiles. Nongame Wildlife Program, Florida Game and Fresh Water Fish Commission, Tallahassee. 18 pp.

Mount, R. H. 1975. The Reptiles and Amphibians of Alabama. Auburn University Agricultural Experiment Station, Auburn. 347 pp.

Nissenson, M., and S. Jonas. 1995. Snake Charm. Harry N. Abrams, Inc., New York. 160 pp.

Palmer, W. M., and A. L. Braswell.1995. Reptiles of North Carolina. The University of North Carolina Press for North Carolina State Museum of Natural Sciences, Chapel Hill and London. 412 pp.

Phillips, C. A., R. A. Brandon, and E. O. Moll. 1999. Field Guide to Amphibians and Reptiles of Illinois. Illinois Natural History Survey, Champaign, Illinois. 282 pp.

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Price, A. H. 1998. Poisonous Snakes of Texas. Texas Parks and Wildlife Press, Austin. 112 pp.

[Sievert], G., and L. Sievert. [1988]. A Field Guide to Reptiles of Oklahoma. Oklahoma Department of Wildlife Conservation, Oklahoma City. 96 pp.

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Smith, H. M., and R. B. Smith. 1993. Synopsis of the Herpetofauna of Mexico. Volume VII. Bibliographic Addendum IV and Index, Bibliographic Addenda II-IV, 1979-1991. University Press of Colorado, Niwot, Colorado. 1082 pp.

Smith, P. A. 1961. The amphibians and reptiles of Illinois. Illinois Natural History Survey Bulletin 28(1):[i-v], 1-298. (Reprinted 1986.)

Somma, L. A. 2003 (in press). Parental Behavior in Lepidosaurian and Testudinian Reptiles: A Literature Survey. Krieger Publishing Company, Malabar, Florida.

Stevenson, H. S. 1976. Vertebrates of Florida. Identification and Distribution. University Presses of Florida, Gainesville. 607 pp.

Tennant, A. 1997. A Field Guide to Snakes of Florida. Gulf Publishing Company, Houston. 257 pp.

Tennant, A., and R. D. Bartlett. 2000. Snakes of North America. Eastern and Central Regions. Gulf Publishing Company, Houston. 588 pp.

Tennant, A., J. E. Werler, J. E. Forks, and G. T. Salmon. 1998. A Field Guide to Texas Snakes. Second Edition. Gulf Publishing Company, Houston. 291 pp. + poster.

Webb, R. G. 1970. Reptiles of Oklahoma. University of Oklahoma Press, Norman. 370 pp.

Werler, J. E., and J. R. Dixon. 2000. Texas Snakes. Identification, Distribution, and Natural History. University of Texas Press, Austin. 437 pp.

Wharton, C. H. 1960. Birth and behavior of a brood of cottonmouths, Agkistrodon piscivorus piscivorus with notes on tail-luring. Herpetologica 16:125-129.

Wharton, C. H. 1966. Reproduction and growth in the cottonmouths, Agkistrodon piscivorus Lacépède, of Cedar Keys, Florida. Copeia 1966(2):149-161.

Wharton, C. H. 1969. The cottonmouth moccasin on Sea Horse Key, Florida. Bulletin of the Florida State Museum, Biological Sciences 14:227-272.

Wright, A. H., and A. A. Wright. 1957. Handbook of Snakes of The United States and Canada. Volumes I-II. Comstock Publishing Associates, Ithaca and London. 1105 pp.

Wright, A. H., and A. A. Wright. 1962. Handbook of Snakes of the United States and Canada. Volume III. Bibliography. A. H. and A. A. Wright, Ithaca. 179 pp. [Reprinted 1979 by Society for the Study of Amphibians and Reptiles, Oxford, Ohio.]

Zaidan, F., III. 2001. Western cottonmouth (Agkistrodon piscivorus leucostoma) sexual dichromatism in northwestern Arkansas. Herpetological Natural History 8(1):79-82.

Other Resources:
Distinguishing the Florida cottonmouth from the Eastern cottonmouth

Chicago Herpetological Society: cottonmouth

Author: Somma, L.A., Fuller, P., and Foster, A.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.