Agkistrodon contortrix

Agkistrodon contortrix. Commonly known as the copperhead, it is a species of pit viper endemic to eastern North America. It is a medium-sized, venomous snake known for its distinctive coppery-red head and hourglass-shaped crossbands. As a member of the subfamily Crotalinae, it possesses characteristic heat-sensing pits between its eyes and nostrils, which aid in hunting endothermic prey.

Description

Adult copperheads typically measure between 61 and 90 centimeters in length, with robust bodies and broad, triangular heads distinct from the neck. Their base color varies from pale tan to pinkish-brown, overlaid with a series of dark, chestnut-brown crossbands shaped like an hourglass or saddle. The head is a uniform copper color, giving the snake its common name. The juveniles are paler and possess a bright yellow or greenish-yellow tail tip, which is used as a caudal lure to attract small prey like frogs and shrews. The eyes have vertically elliptical pupils, a trait shared with other nocturnal vipers. The subcaudal scales are typically divided, and the anal plate is single.

Distribution and habitat

The copperhead has one of the largest ranges of any North American pit viper, extending from southern New England westward to Illinois and southward to the Florida Panhandle and central Texas. Its range broadly overlaps with that of the timber rattlesnake in the Appalachian Mountains. This species occupies a wide variety of habitats but shows a strong preference for deciduous forests, rocky, wooded hillsides, and lowland areas near streams or swamps. It is often found in the Chihuahuan Desert ecoregion within Trans-Pecos Texas and is frequently encountered in suburban areas where its camouflage makes it difficult to detect among leaf litter and garden debris.

Behavior and ecology

Primarily crepuscular and nocturnal during the hot summer months, copperheads become more diurnal in the spring and fall. They are ambush predators, relying on cryptic coloration to remain undetected by prey such as rodents, songbirds, and large insects. They are known to employ caudal luring, especially as juveniles. Copperheads are ovoviviparous, giving birth to live young in late summer or early fall. They often hibernate in communal dens, sometimes with other snake species like the black racer and the rat snake, in rocky crevices or abandoned mammal burrows. Their primary predators include raptors, opossums, skunks, and other snakes.

Venom

The venom of the copperhead is primarily hemotoxic, though it is considered the least potent among North American pit vipers and is rarely fatal to healthy adult humans. The venom contains enzymes like metalloproteinases and phospholipase A2 that disrupt blood clotting and cause local tissue damage, leading to pain, swelling, and ecchymosis. Bites are often "dry," with little to no venom injected, as the snake uses its venom primarily for subduing prey. Antivenom used for treatment is Crotalidae Polyvalent Immune Fab (CroFab), which is also effective against bites from the eastern diamondback rattlesnake and the cottonmouth.

Subspecies

Five subspecies are currently recognized, which vary in coloration, pattern, and geographic range. The northern copperhead (*Agkistrodon contortrix mokasen*) ranges from Massachusetts to Alabama. The southern copperhead (*A. c. contortrix*) is found in the southeastern United States. The broad-banded copperhead (*A. c. laticinctus*) inhabits central Texas and Oklahoma. The Trans-Pecos copperhead (*A. c. pictigaster*) is restricted to the Chihuahuan Desert in Texas. The Osage copperhead (*A. c. phaeogaster*) occupies regions in Missouri, Kansas, and Nebraska. These subspecies were first formally described by herpetologists like Edward Drinker Cope and Leonhard Hess Stejneger.