Eastern Indigo Snake

About the eastern indigo snake

The eastern indigo snake is a large, nonvenomous snake in the subfamily Colubrinae, native to the southeastern United States, where it holds the title of the longest native snake species in the country. It was first described by naturalist John Edwards Holbrook in 1842 and, after decades of being classified as one of 12 subspecies of a single monotypic species, was elevated to full species status in the early 1990s. Its genus name, Drymarchon, translates roughly to "lord of the forest," combining Greek words for forest and ruler; the species name honors James Hamilton Couper, the planter who supplied Holbrook's original specimen from south of the Altamaha River in Georgia.

The snake's common name comes from its glossy, iridescent scales, which appear uniformly blue-black and can flash blackish-purple in bright light; some individuals show reddish-orange to tan coloring on the throat, cheeks, and chin. The longest confirmed specimen measured 2.8 m (9.2 ft), but a typical mature male runs 1.2 to 2.36 m (3.9 to 7.7 ft), averaging 1.58 m (5.2 ft) and 2.2 kg (4.9 lb). Unusually, males average larger than females, likely a result of competition and physical combat between rival males; mature females typically measure 1.1 to 2 m (3.6 to 6.6 ft), averaging 1.38 m (4.5 ft) and 1.5 kg (3.3 lb). Males longer than 1.2 m (4 ft) tend to develop weak keels on several mid-dorsal scale rows, a trait females lack. Despite its size, the sympatric eastern diamondback rattlesnake can outweigh even a very large indigo snake of similar length.

Behavior and diet

Eastern indigo snakes are diurnal, terrestrial, and wide-ranging active foragers, and their cover needs shift with the seasons. From December through April they favor sandhill habitats, often near gopher tortoise burrows they use to escape cold weather; from May through July they move between winter dens and summer territory; and from August through November they're found more often in shady creek bottoms. Summer home ranges can run as large as 273 acres (110 hectares), which means the snakes depend on connected corridors linking sandhills, upland pine-hardwood forest, creek bottoms, and agricultural fields throughout the year. They frequently shelter in gopher tortoise burrows, and when those aren't available they'll use armadillo holes, hollow logs, or debris piles left over from tree-plantation clearing — cover that's often destroyed for appearance's sake even though it's important habitat for both the snake and its prey.

As a carnivore, the eastern indigo snake will overpower almost any small animal it can catch, probing into stump holes and burrows or patrolling wetland edges, and it sometimes kills prey by pressing it against burrow walls. Its diet includes other snakes — even venomous ones, since it's immune to the venom of North American rattlesnakes — along with slugs, turtles, lizards, frogs, toads, fish, small birds, mammals, and eggs. Studies with mice found the snake relies on visual cues of prey rather than airborne scent to trigger investigation. When threatened, it flattens its neck vertically, hisses, and vibrates its tail, but it rarely bites if picked up.

Mating peaks from November through January, though it can run from October through March, and takes place while the snakes are in their sandhill habitat. Females can store live sperm for potentially more than four years, choosing when to fertilize their eggs. A single clutch of 4 to 14 eggs, each 75-100 mm (3-4 in) long, is laid from late April through early June, and hatchlings emerge 600-700 mm (23.5-27.5 in) long. The species matures late for a colubrid, typically not until age three to five and a body length of 5 to 6 feet.

Range and habitat

The eastern indigo snake is found from Florida into southern Georgia and southern Alabama, with the heaviest concentration of Georgia sightings in the sand ridges of the Tufton Upland region of the coastal plain. Its historic range once extended into Mississippi and possibly South Carolina. It favors flatwoods, hammocks, dry glades, stream bottoms, cane fields, and riparian thickets, along with high ground on well-drained sandy soils, and is especially tied to longleaf pine and scrub oak plant communities that include turkey oak, live oak, and sand post oak. In the northern part of its range it's largely restricted to sandhills, where it depends on gopher tortoise burrows for winter shelter, nesting, foraging, and shedding. Its closest relative, the Texas indigo snake, occupies a separate range in southern Texas and Mexico.

Conservation status

The eastern indigo snake carries an IUCN status of Least Concern, but in the United States it's listed as a federally threatened species because of habitat loss, and NatureServe considers it endangered. Alabama listed the species as possibly extirpated within the state as of 2012, though a reintroduction program has since shown signs of success, including a sighting in March 2022. The snake was also effectively eliminated from northern Florida; a restoration effort at the Apalachicola Bluffs and Ravines Preserve released 12 snakes in 2017 after no sightings there since 1982, followed by 20 more in 2018 and 15 more in 2019, in a 10-year collaboration between the Florida Fish and Wildlife Conservation Commission and private partners.

Beyond habitat loss, the species faces a snake fungal disease caused by Ophidiomyces ophiodiicola, which produces lesions on the head and near the vent, and captive populations can suffer from a protozoal parasite, Cryptosporidium serpentis, that causes gastric illness, dehydration, and sometimes death. Humans remain the biggest threat overall: highway deaths, illegal collection for the pet trade, and "gassing" — pouring gasoline into gopher tortoise burrows to flush out rattlesnakes — all take a toll, and the snake's decline is closely tied to the decline of the gopher tortoise, whose burrows it depends on.