Other Taxonomic Groupings
Drymarchon couperi, the eastern indigo snake, is a heavy-bodied, docile, and non-venomous snake. The
longest native snake in North America, it grows to lengths of 1.88 - 2.65 m (6.2 - 8.7 feet) (Ashton and Ashton 1981; King and Krysko 2000). Body color is a uniform iridescent blue-black to black color except for a patch of red to reddish-cream around the chin, throat, and cheeks.
The extent and vibrancy of this patch varies with geographic location. Scales are
large and smooth, with the central 3 - 5 scale rows keeled in adult
males. There are 17 scale rows measured at mid-body, and the
anal plate is undivided. Juveniles measure 43 - 61 cm (17
- 24 inches) at hatching, are typically black, have narrow whitish
to bluish bands along the body, and are more red or cream colored
around the head (USFWS 1999; Conanat and Collins 1991).
Potentially Misidentified Species
Juveniles may be easily confused with southern black racers (Coluber
constrictor priapus) due to the pale patches around the chin
and cheeks. Black pine snakes (Pituophis melanoleucas
lodingi) are similar in color and size, but lack the iridescent
sheen of the indigo snake. They also retain a faint crossbanding
pattern on the tail that indigo snakes lack.
HABITAT AND DISTRIBUTION
The historic range of Drymarchon couperi included the coastal
plains of Georgia, Alabama, Mississippi, and possibly Southern South
Carolina. Currently indigo snakes primarily range throughout
Florida, including the Florida Keys, and into southern Georgia (Lazell
1989; Lawler 1977).
Drymarchon couperi occurs throughout the IRL.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Eastern Indigo snakes are the longest native snakes in the U.S. and grow
to lengths of 1.88 - 2.65 m (Ashton and Ashton 1981; King
and Krysko 2000). Juveniles measure 43 - 61 cm (17 -24 inches) at hatching.
is available regarding the lifespan of wild eastern indigo snakes;
however, captive snakes have been documented to live more than 25
years (Shaw 1959).
Though they occur throughout Florida, eastern indigo snake populations
are declining to the point where they are considered rare in many
couperi reaches sexual maturity at approximately 3 - 4 years
of age (Hallam et al. 1998). In North Florida, breeding occurs
November - April. Wild females lay clutches of 4 - 12 eggs
in May or June (Moler 1992), while captive females have an average
clutch size of 9 -20 (Speake et al. 1987). Hatching takes
place after approximately 3 months, with peaks occurring August
- September. In south-central Florida, breeding occurs June
- January, with egg laying taking place April - July. Hatching
generally occurs from mid-summer through early Fall (USFWS 1999).
Females can apparently store sperm
and delay fertilization of eggs. Carson (1945) reported a
on a female indigo snake that laid a clutch of 5 eggs after having
been isolated for more than 4 years. There have also been
anecdotal reports of parthenogenetic reproduction in virginal snakes
Drymarchon couperi is cold-sensitive and requires shelter when winter temperatures below approximately 10°C (50 °F). Most often refuge is taken in gopher tortoise burrows (Bogert
and Cowles 1947; Speake et al. 1978).
In wetter habitats where gopher tortoises do not occur, indigo snakes take refuge in hollow logs and the burrows of rodents, land crabs, and armadillos (Lawler 1977; Moler 1985a; Layne and Steiner 1996).
Other Physical Tolerances
laboratory conditions, Drymarchon couperi showed a high
susceptibility to desiccation, and thus seeks out cool, underground
burrows or similar cover as shelter against extreme heat and dryness
(Bogert and Cowles 1947; Speake et al. 1978; Moler 1985a).
As they lack venom and do not constrict, eastern indigo snakes attack
any vertebrate small enough to be overpowered and killed with their
strong jaws. They have been observed to flush prey from cover,
then give chase (Layne and Steiner 1996). They also occasionally
climb trees or shrubs in search of prey. The diet includes
toads, frogs, lizards, other snakes (including venomous types),
turtles, turtle eggs, gopher tortoises, small alligators, birds,
and rodents. Juveniles consume primarily invertebrates (USFWS
1999; Layne and Steiner 1996; Steiner et al. 1983).
Drymarchon couperi utilizes a variety of habitat types and shows some preference for open, undeveloped
uplands. Typical habitats include pine flatwoods, scrubby flatwoods, high pine, dry prairie, tropical hardwood hammocks, marshes,
coastal dunes and scrub, and mangrove forests (Steiner et al. 1983;
In Georgia and Northern
Florida, indigo snakes can be temperature-restricted to sandhill
areas where gopher tortoises burrows are available to shelter in
when winter temperatures drop below approximately 10°C.
In peninsular Florida, where winter temperatures are not typically
challenging, indigo snakes are found in all terrestrial habitats
that are not densely developed. Along the coast, indigo snakes
frequently use sandy ridges and hammock areas (Moler 1985b).
Drymarchon couperi move between habitats frequently, especially during the summer and
fall (Moler 1985a), and thus have extensive home ranges. Speake
et al. (1978) reported home range sizes for indigo snakes in Georgia
averaging 4.8 ha in winter (December - April) and 42.9 ha in late
spring and summer (May - July). Moler (1985a) reported that
adult males utilize larger areas then either females or juveniles,
perhaps encompassing 224 ha. Layne and Steiner (1996) reported
male home range size as averaging approximately 74 ha (with a maximum
of 199.2 ha), while females averaged approximately 19 ha (with a
maximum of 48.6 ha).
Drymarchon couperi can often be found in association with
gopher tortoises (Gopherus polyphemus) and other organisms
that share tortoise burrows, including the eastern diamondback rattlesnake
Drymarchon couperi has been listed
as Threatened in the State of Florida since 1971. It has been Federally listed as Threatened since Jan 31, 1978. The decline of eastern indigo snakes is primarily the result of over-harvesting for the pet trade, but habitat loss and degradation, and the gassing of tortoise burrows to collect rattlesnakes have also heavily impacted the species (Speake and Mount 1973; Speake and McGlincy 1981).
Law enforcement of prohibitions against unauthorized take has reduced pressure on the indigo snake, but has not eliminated it (Moler 1992). Because this snake has a large home range, it may be especially susceptible to habitat loss and fragmentation (Lawler 1977; Moler 1985a). Some estimates suggest that habitat losses of approximately 5% per year continue to occur (Lawler 1977). Increased human population growth also increases the possibility of increased snake mortality due to deaths from property owners and domestic pets.
It is expected that the increasing trend toward altering natural areas for agricultural, residential and commercial purposes will
result in a large number of isolated groups which cannot support a sufficient number of individuals to ensure continued survival.
Recovery of Drymarchon couperi requires protection and preservation
of large expanses of unaltered habitat (USFWS 1999). However,
relatively little is currently known about the minimum population
size required to maintain and recover the species, though research
and population modeling efforts are underway to address these issues.
Management activities being currently undertaken include prescribed burning to maintain optimum habitat quality, maintenance of a captive breeding colony, public outreach and education, and landowner cooperation to conserve snake populations on privately held lands.
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Carson, H. 1945. Delayed fertilization in a captive indigo snake with a note feeding and shedding. Copeia 1945(4):222-224.
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Hallam, C.O., K. Wheaton, and R. Fischer. 1998. Species profile: Eastern indigo snake (Drymarchon corais couperi) on military installations in the Southeastern United States. Technical report SERDP-98-2, March 1998. Strategic Environmental Research and Development Program, U.S. Army Corps. of Engineers, Waterways Experiment Station, Vicksburg, MS.
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Moler, P.E. 1985a. Home range and seasonal
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Speake, D.W. 1993. Indigo snake recovery plan revision. Final report to the U.S. Fish and Wildlife Service; Jacksonville, Florida.
Speake, D.W., and R.H. Mount. 1973. Some possible ecological effects of "rattlesnake roundups" in the southeastern coastal plain. Proceedings of the annual conference of the Southeastern Association of Fish and Wildlife Agencies 27:267-277.
Speake, D.W., J.A. McGlincy, and T.R. Colvin. 1978. Ecology and management of the eastern indigo snake in Georgia:
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Steiner, T.M., O.L. Bass, Jr., and J.A. Kushlan.
1983. Status of the eastern indigo snake in southern Florida National
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National Park; Homestead, Florida.
U.S. Fish and Wildlife Service USFWS). 1982. Eastern indigo snake recovery plan. U.S. Fish and Wildlife Service, Atlanta, Georgia.
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