"Copperhead" can refer to two extremely distinct species of snake, to the North American Agkistrodon Contortorix, a member of the Crotalinae (pit viper) subfamily; or to Austrelaps, a genus of venomous elapid snakes native to the relatively fertile temperate southern and eastern part of the Australian continent. As of now, the Austrelaps spp. are another writeup for another day. This writeup will address only the Agkistrodon species of North America.
Adult copperheads usually grow to a total length of 50-95 cm, although some specimens have exceeded 1 m. Males are usually larger than females. The maximum reported length for the subspecies A. c. mokasen is 134.6 cm. Likewise, the maximum reported length for A. c. controtrix is 132.1 cm.
The body is relatively stout, and the head is broad and distinct from the neck. Because the snout slopes down and back, it usually appears less blunt than that of the cottonmouth, A. piscivoris. Owing to this, the top of the head usually extends further forward than the mouth.
The scalation includes 21-25 (with an average of 23) rows of dorsal scales at midbody, 138-157 ventral scales in both sexes, and 38-62/37-57 subcadual scales in males/females. The subcaudals are usually single, but the percentage thereof decreases clinically 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 supralabial scales and 8-13 sublabial scales.
The color pattern consists of a pale tan to pinkish tan ground color that becomes darker toward the midline, overlaid with a series of 10-18 crossbands. 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, 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.
Common names for the snakes of the Agkistrodon family include: Copperhead, chunk head, death adder, highland moccasin, dry moccasin, narrow-banded copperhead, northern copperhead, pilot snake, poplar leaf, red oak, red snake, southeastern copperhead, white oak snake, American copperhead, southern copperhead, and cantil cobrizo.
The copperhead is found in the majority of the Southern United States, including Texas, Oklahoma, Kansas, Missouri, Arkansas, Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina, North Carolina, Tennessee, Kentucky, Virginia, West Virginia, Illinois, Indiana, Ohio, Iowa, Pennsylvania, Maryland, New Jersey, Delaware, New York, Connecticut and Massachusetts. In Mexico it occurs in Chihuahua and Coahuila.
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. 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 brooks.
A. contortrix is currently classified as Least Concern (LC) on the IUCN Red List of Threatened Species. 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.
Roughly 90% of the copperhead diet consists of small rodents, such as mice and voles. On observation and in captivity, they have also shown fondness for large insects and frogs, and though mainly a terrestrial snake, they have been known to climb trees to gorge on emerging cicadas. Like all pit vipers, A. contortrix is generally an ambush predator. It will assume a promising position and wait for sutible prey to arrive. One exception to ambush foraging occurs when copperheads feed on insects. When hunting insects, copperheads will actively pursue their prey.
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 moving away, and as a result many bites occur from people unknowingly stepping on or near them. This tendency to freeze 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.
Copperheads breed 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 about 20 cm long: a typical litter is 4 to 7, but it 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 yellow-marked tip to the tail, which is used to lure lizards and frogs. Studies have shown that male A. contortrix has longer tongue fork tine length than females during the breeding season to aid in chemoreception of males searching females.
Although venomous, these snakes are generally non-aggressive and bites are almost never fatal. Copperhead venom has an estimated lethal dose of around 100 mg. 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 intense 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 and also stops the migration of the tumors to other sites. It will probably be ten or more years before contortrostatin is used in practical treatment but it has shown to be a very promising drug in laboratory studies.
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 very few reported deaths from copperhead bites all involved multiple snakes. Pain management, antibiotics, and medical supervision in the case of complications is usually the course of action.
Due to the somewhat technical nature of this writeup, I should note that the entire thing was shamelessly reworked from an old paper I wrote, entitled "An Overview of Agkistrodon Contortorix", with many changes made to reduce the overall length. In reworking, I tried to make it extremely accessible to everyone, but there are some terms (for instance, terms describing types of scalation, like supralabial and subcadual) that are necessary. I apologize for any inconvience.