The eastern copperhead (Agkistrodon contortrix), also known simply as the copperhead, is a widespread species of venomous snake, a pit viper, endemic to eastern United States of America; it is a member of the subfamily Crotalinae in the family Viperidae.
The eastern copperhead has distinctive, dark brown, hourglass-shaped markings, overlaid on a light reddish brown or brown/gray background. The body type is heavy, rather than slender. Neonates are born with green or yellow tail tips, which progress to a darker brown or black within one year. Adults grow to a typical length (including tail) of .
In most of the United States of America, the eastern copperhead favors deciduous forest and mixed woodlands. It may occupy rock outcroppings and ledges, but is also found in low-lying, swampy regions. During the winter, it hibernates in dens or limestone crevices, often together with timber rattlesnakes and black rat snakes. The eastern copperhead is known to feed on a wide variety of prey, including invertebrates (primarily arthropods) and vertebrates. Like most pit vipers, the eastern copperhead is generally an ambush predator; it takes up a promising position and waits for suitable prey to arrive.
As a common species within its range, it may be encountered by humans. Unlike other viperids, it often "freezes" instead of slithering away and fleeing, due to its habit of relying on excellent camouflage. Bites occur due to people unknowingly stepping on or near them. Copperhead bites account for half of the treated snake bites in the United States.
Five subspecies have been recognized in the past, but recent genetic analysis has yielded new species information.
Etymology Its generic name is derived from the Greek words ankistron "hook, fishhook" and odon, variant of odous "tooth"., , . The trivial name, or specific epithet, comes from the Latin contortus (twisted, intricate, complex), which is usually interpreted to reference the distorted pattern of darker bands across the snake's back, which are broad at the lateral base, but "pinched" into narrow hourglass shapes in the middle at the vertebral area.Campbell JA, Lamar WW (2004). The Venomous Reptiles of the Western Hemisphere. Ithaca and London: Comstock Publishing Associates. .Lemos Espinal, J.A., G.R. Smith, J.R. Dixon, and A. Cruz. (2015). Amphibians and Reptiles of Sonora, Chihuahua, and Coahuila, Mexico. Distrito Federal, Mexico. .
Description Adults grow to a typical length (including tail) of . Some may exceed , although that is exceptional for this species.Ernst, Carl H.; Barbour, Roger W. (1989). Snakes of Eastern North America. Fairfax, Virginia: George Mason University Press. . Males do not typically exceed and weigh from , with a mean of roughly . Females do not typically exceed ,Palmer, William M.; Braswell, Alvin L. (1995). Reptiles of North Carolina. Chapel Hill and London: University of North Carolina Press. .Stejneger, L (1895). The Poisonous Snakes of North America. Washington, District of Columbia: United States Government Printing Office. and have a mean body mass of . The maximum length reported for this species is for A. c. mokasen (Ditmars, 1931). Brimley (1944) mentions a specimen of A. c. mokasen from Chapel Hill, North Carolina, that was "four feet, six inches" (137.2 cm), but this may have been an approximation. The maximum length for A. c. contortrix is (Conant, 1958).
The body is relatively stout and the head is broad and distinct from the neck. Because the snout slopes down and back, it appears less blunt than that of the cottonmouth, A. piscivorus. Consequently, the top of the head extends further forward than the mouth.Gloyd HK, Conant R (1990). Snakes of the Agkistrodon Complex: A Monographic Review. Society for the Study of Amphibians and Reptiles. LCCN 89-50342. .
The escalation includes 21–25 (usually 23) rows of dorsal scales at midbody, 138–157 ventral scales in both sexes, and 38–62 and 37–57 subcaudal scales in males and females, respectively. The subcaudals are usually single, but the percentage thereof decreases clinally from the northeast, where about 80% are undivided, to the southwest of the geographic range where as little as 50% may be undivided. On the head are usually 9 large symmetrical plates, 6–10 (usually 8) supralabial scales, and 8–13 (usually 10) sublabial scales.
The color pattern consists of a pale tan to pinkish-tan ground color that becomes darker towards the foreline, overlaid with a series of 10–18 (13.4) crossbands. Characteristically, both the ground color and crossband pattern are pale in A. c. contortrix. These crossbands are light tan to pinkish-tan to pale brown in the center, but darker towards the edges. They are about two scales wide or less at the midline of the back, but expand to a width of 6–10 scales on the sides of the body. They do not extend down to the ventral scales. Often, the crossbands are divided at the midline and alternate on either side of the body, with some individuals even having more half bands than complete ones. A series of dark brown spots is also present on the flanks, next to the belly, and are largest and darkest in the spaces between the crossbands.
The belly is the same color as the ground color, but may be a little whitish in part. At the base of the tail are one to three (usually two) brown crossbands followed by a gray area. In juveniles, the pattern on the tail is more distinct: 7–9 crossbands are visible, while the tip is yellow. On the head, the crown is usually unmarked, except for a pair of small dark spots, one near the midline of each parietal scale. A faint postocular stripe is also present; diffuse above and bordered below by a narrow brown edge.
Several aberrant color patterns for A. c. contortrix, or populations that intergrade with it, have also been reported. In a specimen described by Livezey (1949) from Walker County, Texas, 11 of 17 crossbands were not joined middorsally, while on one side, three of the crossbands were fused together longitudinally to form a continuous, undulating band, surmounted above by a dark stripe that was 2.0–2.5 scales wide.
In another specimen, from Lowndes County, Alabama, the first three crossbands were complete, followed by a dark stripe that ran down either side of the body, with points of pigment reaching up to the midline in six places, but never getting there, after which the last four crossbands on the tail were also complete. A specimen found in Terrebonne Parish, Louisiana had a similar striped pattern, with only the first and last two crossbands being normal.
Distribution and habitat The eastern copperhead is found in North America; its range within the United States is in Alabama, Arkansas, Connecticut, Delaware, District of Columbia, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Mississippi, Missouri, Nebraska, New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Texas, Virginia, and West Virginia. In Mexico, it occurs in Chihuahua and Coahuila. The type locality is "Carolina". Schmidt (1953) proposed the type locality be restricted to "Charleston, South Carolina".McDiarmid RW, Campbell JA, Touré TA (1999). Snake Species of the World: A Taxonomic and Geographic Reference, Volume 1. Washington, District of Columbia: Herpetologists' League. (series). (volume).
Unlike some other species of North American pit vipers, such as the timber rattlesnake and massasauga, the copperhead has mostly not re-established itself north of the terminal moraine after the last glacial period (the Wisconsin glaciation),Anonymous. (year?). Copperhead Snake, Life History Notes. Ohio Division of Wildlife. Publication 373 (399). though it is found in southeastern New York and southern New England, north of the Wisconsin glaciation terminal moraine on Long Island.
Historically, kingsnakes have been major copperhead predators. Recent copperhead abundance has been linked to declining kingsnake populations in those areas.
Eastern copperheads are habitat generalists which are species able to survive in different habitats (fragmented and unfragmented). Within its range, it occupies a variety of different habitats. In most of North America, it favors deciduous forest and mixed woodlands. It is often associated with rock outcroppings and ledges, but is also found in low-lying, swampy regions. During the winter, it hibernates in dens or limestone crevices, often together with timber rattlesnakes and black rat snakes. In the states around the Gulf of Mexico, however, this species is also found in coniferous forest. In the Chihuahuan Desert of West Texas and northern Mexico, it occurs in riparian habitats, usually near permanent or semipermanent water and sometimes in dry arroyos (brooks). Habitat fragmentation has been found to impair Eastern Copperhead access to feeding, brumation, and reproduction sites. In a tracking study, copperheads studied in fragmented areas never left the area they were first caught in.
Conservation status This species is classified as least concern on the IUCN Red List of Threatened Species (v3.1, 2001). This means that relative to many other species, it is not at risk of extinction in the near future. The population trend was stable when assessed in 2007. Their venom has potential medicinal value to humans.
Behavior In the Southern United States, copperheads are nocturnal during the hot summer, but are commonly active during the day during the spring and fall. Unlike other viperids, they often "freeze" instead of slithering away, and as a result, many bites occur due to people unknowingly stepping on or near them. This tendency to freeze most likely evolved because of the extreme effectiveness of their camouflage. When lying on dead leaves or red clay, they can be almost impossible to notice. Eastern Copperheads are more likely to either remain in crypsis or flee in the presence of a human rather than display defensive behavior. Generally nonaggressive, will only strike if threatened as a last resort. Like most other New World vipers, copperheads exhibit defensive tail vibration behavior when closely approached. This species is capable of vibrating its tail in excess of 40 times per second— faster than almost any other non-rattlesnake snake species.
Diet and feeding behavior
The eastern copperhead is a diet generalist and is known to feed on a wide variety of prey, including invertebrates (primarily arthropods) and vertebrates. A generalized ontogenetic shift in the diet occurs, with juveniles feeding on higher percentages of invertebrates and ectotherms, and adults feeding on a higher percentage vertebrate endotherms. Both juveniles and adults, though, feed on invertebrates and vertebrates opportunistically. The diet is also known to vary among geographic populations.Ernst, Carl H. and Evelyn M. Ernst. (2011). Venomous Reptiles of the United States, Canada, and Northern Mexico, Volume 1. The Johns Hopkins University Press. Baltimore, Maryland.
Studies conducted at various locations within the range of the eastern copperhead (A. contortrix), including Tennessee, Kentucky, Kansas,Fitch, H.S. (1982). "Resources of a snake community in prairie-woodland habitat of northeastern Kansas", pp. 83–97 in N. Scott, Jr. (ed.), Herpetological communities. U.S. Fish and Wildlife Service, Wildlife Research Report, 13. and Texas, identified some consistently significant prey items included cicadas (Tibicen), caterpillars (Lepidoptera), lizards (Sceloporus and Scincella), voles (Microtus), and mice (Peromyscus). Accounts of finding large numbers of copperheads in bushes, vines, and trees seeking newly emerged cicadas, some as high as 40 feet above ground, have been reported from Texas by various herpetologists.Werler, John E. and James R. Dixon. (2000). Texas Snakes: Identification, Distribution, and Natural History. Austin, Texas: University of Texas Press.