Drymarchon couperi HOLBROOK 1842
Eastern indigo snake (English)
The Eastern Indigo Snake (Drymarchon couperi) is a large shiny bluish black snake, sometimes with chin, throat, and sides of head with cream, reddish, or orange brown. It is the largest North American snake, reaching about 150 to 210 cm (record 263 cm). The scales are normally smooth, but some males, especially larger individuals, have faintly keeled scales on as many as five middorsal rows, starting at about the second quarter of the body; the anal plate is undivided. The third from last upper labial is wedge-shaped and cut off above by contact between adjacent labials. Young are like adults, but often with much more reddish on head and forward part of belly, 43 to 66 cm at hatching. (Behler 1979; Conant and Collins 1991)
The current stronghold for this threatened species is southeastern Georgia and peninsular Florida. It persists in lower numbers in Florida's panhandle, but is functionally extinct in Alabama and Mississippi. (USFWS 2008)
Conservation and Management
The Eastern Indigo Snake was listed as threatened under the U.S. Endangered Species Act in 1978 (Federal Register, 43 FR 4026-4029).
Because of their large home ranges and other behavioral traits, it is estimated that maintaining a viable population of Eastern Indigo Snakes requires at least 1000 hectares. The lack of reliable survey methods for this snake has made it difficult to obtain basic demographic and trend data and carry out effective conservation planning. One intriguing possibility that has shown at least some promise for locating Indigo snakes has been training dogs to track them. (USFWS 2008 and references therein)
Although development has been generally extremely harmful to the Eastern Indigo Snake, in south Florida, agricultural sites such as sugar cane fields and canal banks through citrus groves created in former wetland areas are occupied by Eastern Indigo Snakes. Historically, these snakes would have occupied only higher elevation sites within the wetlands. Agriculture and its associated canal systems, however, have brought increased numbers of rodents and other snake species that are eaten by Eastern Indigos, resulting in higher densities of Eastern Indigo Snakes in these areas than would have been present in the past. Efforts to restore natural wetlands in some of these areas may actually reduce resident populations of Eastern Indigo Snakes. (USFWS 2008)
Current efforts to secure the future of the Eastern Indigo Snake are focused on land acquisition, captive breeding snakes to establish new populations in the wild, and habitat management (USFWS 2008).
Loss of native habitat supporting Eastern Indigo Snakes is ongoing as a result of development and urbanization. Habitat loss is especially problematic for this species because of its relatively large home range. (USFWS 2008)
When cornered, the Eastern Indigo Snake flattens its neck vertically (not horizontally as in the hognose snakes), hisses, and vibrates its tail, producing a rattling sound. When caught, it seldom attempts to bite. Captive Eastern Indigo Snakes are usually restless and keep on the move when handled. (Conant and Collins 1991)
All other plain black snakes within the range of the Eastern Indigo Snake have keeled scales, a divided anal plate, or both (Conant and Collins 1991).
The Eastern Indigo Snake is found in pine woods, turkey oak, and palmetto stands near water, orange groves, and tropical hammocks (Behler 1979). It occurs mainly in large, unsettled areas (Conant and Collins 1991). Based on their work with Eastern Indigo Snakes in southeastern Georgia, Hyslop et al. (2009) suggest that availability of Gopher Tortoise (Gopherus polyphemus) burrows, which are used by the snakes as shelters, may be a limiting factor for the Eastern Indigo Snake in the northern part of its range (see also, e.g., Stevenson et al. 2003).
In a study in Georgia, Indigo Snake populations were typically associated with deep, excessively drained sandy soils on sand ridges along major coastal plain streams; winter sightings occurred almost exclusively on sandhills and in association with Gopher Tortoises (Diemer and Speake 1983).
Home range estimates for Eastern Indigo Snakes in peninsular Florida ranged from 1.9 to 150 hectares for females and 1.6 to 327 hectares for males. Summer home ranges tend to be much larger than winter home ranges. A recent telemetry study in Georgia estimated home ranges of 35 to 354 hectares for females and 140 to 1530 hectares for males. Especially in fall and winter, Eastern Indigo Snakes are often associated with Gopher Tortoise burrows. These snakes seem to avoid paved roads, urban areas, and deciduous forest. Eastern Indigo Snakes exhibit a homing instinct and may return annually to previously used winter dens. (USFWS 2008 and references therein)
The Eastern Indigo Snake (Drymarchon couperi) is found in the eastern United States from southeastern Georgia, peninsular Florida and the lower Keys west to southeastern Mississippi; it was apparently released outside its native range in extreme southern Mississippi by governmental agencies (Conant and Collins 1991). Historically, this species occurred throughout Florida and in the coastal plain of Georgia, Alabama, and Mississippi (USFWS 2008 and references therein).
The diet of the Indigo Snake includes small mammals, birds, frogs, snakes (including even cottonmouths and rattlenakes), lizards, and young turtles. The Indigo Snake is not a constrictor, instead immobilizing food with its jaws. (Behler 1979; Conant and Collins 1991)
Although the diet consists mainly of vertebrates, based on a single record Rossi and Lewis (1994) suggested that in some microhabitats Philomycus slugs could be an important food source for hatchling and juvenile Eastern Indigo Snakes.
The Eastern Indigo Snake is long-lived; one captive individual lived nearly 26 years (Behler 1979).
The Eastern Indigo Snake mates from November to February. It deposits 5 to 12 leathery eggs, 76 to 102 mm long, in April or May. Hatchlings appear in late July to October. (Behler 1979)
Sexual maturity is reached at about 1.5 meters in length. Two captive females bred at 40 and 41 months of age. Average clutch size of 20 females removed from the wild and laying eggs the following spring was 9.4 eggs. In captivity, Eastern Indigo Snakes typically lay eggs every year. (USFWS 2008 and references therein)
Foster et al. (2000) studied the parasites of 21 Eastern Indigo Snakes in Florida, identifying 19 different parasites that included 2 species of trematodes, 3 cestodes, 10 nematodes, 2 acanthocephalans, 1 pentastomid, and 1 tick.
Hyslop et al. (2009) and others have found that Eastern Indigo Snakes are often associated with the burrows of Gopher Tortoises (Gopherus polyphemus).
Evolution and Systematics
Systematics and Taxonomy
Although at the time it was listed as a federally threatened species the Eastern Indigo Snake was treated as a subspecies, Drymarchon corais couperi, it is now accepted as a full species, Drymarchon couperi (USFWS 2008 and references therein).
- Coluber couperi HOLBROOK 1842 (synonym)
- Drymarchon corais couperi CONANT 1991 (synonym)
- Georgia Couperi BAIRD 1853 (synonym)