Agkistrodon contortrix

Agkistrodon contortrix
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Suborder:	Serpentes
Family:	Viperidae
Genus:	Agkistrodon
Species:	A. contortrix
Binomial name
Agkistrodon contortrix (Linnaeus, 1766)
Synonyms
Boa contortrix Linnaeus, 1766 Scytale contortrix – Sonnini & Latreille, 1801 Scytale Cupreus Rafinesque, 1818 Scytale cupreus – Say, 1819 Tisiphone cuprea – Fitzinger, 1826 [Cenchris] marmorata F. Boie, 1827 Acontias atrofuscus Troost, 1836 [Toxicophis atrofuscus] – Troost, 1836 T[rigonocephalus] cenchris Schlegel, 1837 Trigonocephalus Contortrix – Holbrook, 1838 Trigonocephalus atro-fuscus – Holbrook, 1842 Cenchris contortrix – Gray, 1842 Cenchris atrofuscus – Gray, 1849 Agkistrodon contortrix – Baird & Girard, 1853 T[rigonocephalus] histrionicus A.M.C. Duméril & Bibron, 1853 Ancistrodon contortrix – Baird, 1854 Agkistrodon contorting Abbott, 1869 (ex errore) Ancistrodon atrofuscus – Cope, 1875 Agkistrodon atrofuscus – Yarrow, 1882 [Ancistrodon contortrix] Var. atrofuscus – Garman, 1884 Ancistrodon contortrix – Boulenger, 1896 Agkistrodon contortirix Keim, 1914 (ex errore) Agkistrodon mokasen cupreus – Gloyd & Conant, 1938 Agkistrodon contortrix contortrix – Klauber, 1967 Ancistrodon contortrix contortrix – Schmidt, 1953[2]

Agkistrodon contortrix is a species of venomous snake endemic to Eastern North America, a member of the Crotalinae (pit viper) subfamily. The common name for this species is the copperhead. The behavior of Agkistrodon contortrix may lead to accidental encounters with humans. Five subspecies are currently recognized, including the nominate subspecies described here.^[3]

Description

Detail of head

Adults grow to an average length (including tail) of 50–95 cm (20–37 in). Some may exceed 1 m (3.3 ft), although that is exceptional for this species.^[4] Males are usually larger than females. Good-sized adult males usually do not exceed 74 to 76 cm (29 to 30 in), and females typically do not exceed 60 to 66 cm (24 to 26 in).^[5][6] In one study, males were found to weigh from 101.5 to 343 g (3.58 to 12.10 oz), with a mean of roughly 197.4 g (6.96 oz).^[7] According to a different study, females have a mean body mass of 119.8 g (4.23 oz).^[8] The maximum length reported for this species is 134.6 cm (53.0 in) 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 132.1 cm (52.0 in) (Conant, 1958).^[9]

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.^[10]

The scalation includes 21–25 (usually 23) rows of dorsal scales at midbody, 138–157 ventral scales in both sexes and 38–62/37–57 subcaudal scales in males/females. 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 there are usually 9 large symmetrical plates, 6–10 (usually 8) supralabial scales and 8–13 (usually 10) sublabial scales.^[9]

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 2 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 there are 1–3 (usually 2) 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.^[10]

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 2–2.5 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 by Ernest A. Liner, had a similar striped pattern, with only the first and last two crossbands being normal.^[10]

Common names

Common names for A. contortrix include: copperhead (snake), chunk head, highland moccasin, (dry-land) moccasin, narrow-banded copperhead, northern copperhead, pilot snake, poplar leaf, red oak, red snake, southeastern copperhead, white oak snake,^[11] American copperhead,^[12] southern copperhead,^[10] and cantil cobrizo (Spanish).^[3]

Distribution and habitat

It is found in the United States in the states of Alabama, Arkansas, Connecticut, Delaware, Northern Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Ohio, Oklahoma, Maryland, Massachusetts, Mississippi, Missouri, Nebraska, New Jersey, New York, North Carolina, Pennsylvania, South Carolina, Tennessee, East 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".^[2]

Unlike some other species of North American pit vipers, such as timber rattlesnake and Sistrurus catenatus, Agkistrodon contortrix has mostly not reestablished itself north of the terminal moraine after the last glacial period (the Wisconsin glaciation),^[13] though it is found in southeastern New York State and southern New England, north of the Wisconsin glaciation terminal moraine on Long Island.

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, in limestone crevices, often together with timber rattlesnakes and black rat snakes.^[14] 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).^[9]

Conservation status

This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2001).^[1] Species are listed as such due to their wide distribution, presumed large population, or because it is unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend was stable when assessed in 2007.^[15]

Behavior

Southern copperhead, A. c. contortrix, at the southern limit of its range, in Liberty Co., Florida, camouflaged in dead leaves

Like all pit vipers, A. contortrix is generally an ambush predator: it takes up a promising position and waits for suitable prey to arrive. One exception to ambush foraging occurs when copperheads feed on insects such as caterpillars and freshly molted cicadas. When hunting insects, copperheads actively pursue their prey.^[16] Juveniles use a brightly colored tail to attract frogs and perhaps lizards, a behavior termed caudal luring (see video: ). In the Southern United States, they are nocturnal during the hot summer months, but are commonly active during the day during the spring and fall.

Like most North American viperids, these snakes prefer to avoid humans and, given the opportunity, will leave the area without biting. However, unlike other viperids they will often "freeze" instead of slithering away, and as a result, many bites occur from people unknowingly stepping on or near them.^[17] 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. They will frequently stay still even when approached closely, and will generally strike only if physical contact is made. 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.^[18][19] Copperheads may release a cucumber-smelling musk if touched.^[14]

Feeding

Roughly 90% of its diet consists of small rodents, such as mice and voles. They have also shown fondness for large insects and frogs, and though highly terrestrial, have been known to climb trees to gorge on emerging cicadas.

Reproduction

A. contortrix breeds in late summer, but not every year: sometimes a female will produce young for several years running, then not breed at all for a time. They give birth to live young, each of which is about 20 cm (7.9 in) in total length. The typical litter size is 4 to 7, but there can be as few as one, or as many as 20. Their size apart, the young are similar to the adults, but lighter in color, and with a yellowgreen-marked tip to the tail, which is used to lure lizards and frogs.

A study has shown that A. contortrix males have longer tongue tine lengths than females during the breeding season which may aid in chemoreception of males searching for females.^[20]

Facultative parthenogenesis

The effects of central fusion and terminal fusion on heterozygosity

Parthenogenesis is a natural form of reproduction in which growth and development of embryos occur without fertilization. A. contortrix can reproduce by facultative parthenogenesis, that is, they are capable of switching from a sexual mode of reproduction to an asexual mode.^[21] The type of parthenogenesis that likely occurs is "automixis with terminal fusion," a process in which two terminal products from the same meiosis fuse to form a diploid zygote. This process leads to genome wide homozygosity, expression of deleterious recessive alleles and often to developmental failure (inbreeding depression). Both captive-born and wild-born A. contortrix appear to be capable of this form of parthenogenesis.^[21]

Venom

Although venomous, these snakes are generally not aggressive and bites are rarely fatal. Copperhead venom has an estimated lethal dose of around 100 mg, and tests on mice show its potency is among the lowest of all pit vipers, and slightly weaker than that of its close relative, the cottonmouth. Copperheads often employ a "warning bite" when stepped on or agitated and inject a relatively small amount of venom, if any at all. "Dry bites" involving no venom are particularly common with the copperhead, though all pit vipers are capable of a dry bite.

Bite symptoms include extreme pain, tingling, throbbing, swelling, and severe nausea. Damage can occur to muscle and bone tissue, especially when the bite occurs in the outer extremities such as the hands and feet, areas in which there is not a large muscle mass to absorb the venom. A bite from any venomous snake should be taken very seriously and immediate medical attention sought, as allergic reaction and secondary infection are always possible.

The venom of the southern copperhead has been found to hold a protein called "contortrostatin" that halts the growth of cancer cells in mice and also stops the migration of the tumors to other sites.^[22] However, this is an animal model, and further testing is required to verify safety and efficacy in humans.^[23]

Although technically the antivenin CroFab could be used to treat an envenomation, it is usually not administered for copperheads, as the risk of complications of an allergic reaction to the treatment are greater than the risk from the snakebite itself in most cases. The antivenin can cause an immune reaction called serum sickness. Pain management, antibiotics, and medical supervision in the case of complications is usually the course of action.^[24] In 2002, an Illinois poison control center report on the availability of antivenin stated it used 1 Acp to 5 Acp depending on the symptoms and circumstances. The symptoms of a mild envenomation include swelling of the hand, mild cellulitis, and respiratory distress. The symptoms of a moderate envenomation would include swelling of the hand, vomiting, mild bleeding, ecchymosis, diaphoresis, sinus tachycardia, and hypotension.^[25]

Subspecies

Gallery

Habitats	Isolated	Closeups
Broad-banded copperhead	Southern copperhead	At the St. Louis Zoo
Copperhead crossing river in Virginia Beach	Southern copperhead in Covington, Georgia, at Bert Adams Scout Reservation	Northern copperhead
Southern copperhead, approaching a cicada (in Arkansas)	Southern copperhead consuming cicada (Arkansas)	Southern copperhead close up (in Arkansas)
Southern copperhead

See also

• List of crotaline species and subspecies
• Crotalinae by common name
• Crotalinae by taxonomic synonyms
• Snakebite

References

Further reading

External links

Wikimedia Commons has media related to Agkistrodon contortrix.

Wikisource has the text of the 1879 American Cyclopædia article Copperhead.

• Agkistrodon contortrix at the Reptarium.cz Reptile Database. Accessed 9 August 2007.
• Copperhead on Reptiles and Amphibians of Iowa