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Drymarchon couperiEastern Indigo Snake

By Anika Gooch and Meredith Ranney

Geographic Range

Eastern indigo snakes are most common in Florida and the southern regions of Georgia, although they used to occur throughout much of Alabama, Texas, and South Carolina, as well. Populations in those areas have largely been lost due to habitat destruction, poaching, and killing of these snakes. (Daerr, 1999; Diemer and Speake, 1983; Stevenson, et al., 2003)

Habitat

Eastern indigo snakes can be found in a variety of environments including pine and scrubby flatwoods, high pine, dry prairie, tropical hardwood hammocks, edges of freshwater marshes, agricultural fields, coastal dunes, and human-altered habitats. These snakes thrive more in wetland environments, as opposed to xeric conditions. Often eastern indigo snakes can be found living in the same habitat as gopher tortoises. Eastern indigo snakes use gopher tortoise burrows for shelter in the xeric habitats where gopher tortoises are found. In more moist habitats, eastern indigo snakes take shelter in hollowed root channels, hollow logs, or the burrows of rodents, armadillos, or land crabs. One study (Smith 1987) concluded that eastern indigo snakes live in different habitats throughout the year and at different stages of their lives. For example, adults and juveniles use different burrow habitats. ("Eastern Indigo Snake: Drymarchon corais couperi", 1999; Daerr, 1999; Diemer and Speake, 1983; Stap, 2001; Stevenson, et al., 2003)

Physical Description

Eastern indigo snakes are the largest snakes in the United States and the largest, non-venomous snakes in the southeastern United States. Eastern indigo snakes are uniformly black with the exception of a red or cream colored area on the chin, throat, and, occasionally, the cheeks. The scales are smooth and large, typically with 17 scale rows at the mid body. Adults typical reach between 157.2 and 213.36 cm long. The record, however, is 280.4 cm long. Eastern indigo snakes are sexually dimorphic, with males growing longer than females. Eastern indigo snake young are similar in appearance, with the exception of a white band around their body. These snakes are commonly confused with with racers. Racers differ from eastern indigo snakes in several aspects: racers are rarely over 121.9 cm long, they are often thinner and have a dull black coloration with white or brown throats. ("Eastern Indigo Snake: Drymarchon corais couperi", 1999; "Welcome to Zipcode Zoo", 2009; Murphy, 2003)

  • Sexual Dimorphism
  • male larger
  • Range mass
    14 to 30 g
    0.49 to 1.06 oz
  • Average mass
    24 g
    0.85 oz
  • Range length
    152.4 to 213.36 cm
    60.00 to 84.00 in
  • Average length
    174.7 cm
    68.78 in

Development

Eastern indigo snakes are sexually dimorphic in growth as well. Males grow to larger sizes and females may halt growth to focus their energy on maintaining the production of eggs. Growth rates are higher in younger individuals. (Stevenson, et al., 2003; Ditmars, 1939; Stevenson, et al., 2003)

Reproduction

Female eastern indigo snakes signal their readiness to mate by producing pheromones. When the scent is picked up by a male indigo snake, they track down the scent until they come into contact with the female. If other males are present, they will typically engage in ritual combat dances. During these dances, both males will intertwine their bodies and try to force the other's head to the ground. The winner mates with the female. Eastern indigo snakes have a polygynandrous mating system; males and females have multiple mates. (Murphy, 2003; Stevenson, et al., 2003)

In northern Florida, where most research on reproduction cycles has been conducted, the breeding season is from November to April. Females deposit their eggs from May to June. Females lay from 4 to 12 eggs, usually in vacated animal burrows, such as those of gopher tortoises, fallen logs, or some other sheltered burrow. Young hatch in about 3 months, usually in August and September. The breeding season may be extended in parts of south central Florida. Some researchers suggest that can store sperm and delay fertilization, but this idea has yet to be supported by evidence. ("Eastern Indigo Snake: Drymarchon corais couperi", 1999; "Environmental & Extension Services - Natural Resources: Florida Eastern Indigo Snake (Drymarchon corais couperi)", 2001; Smith, 2002)

  • Breeding interval
    Eastern indigo snakes breed once a year.
  • Breeding season
    Eastern indigo snakes mate from November to April and lay eggs in May and June.
  • Range number of offspring
    4 to 12
  • Average number of offspring
    7
  • Average age at sexual or reproductive maturity (female)
    3-4 years
  • Average age at sexual or reproductive maturity (male)
    3-4 years

Eastern indigo snake hatchlings are born at an average size of 30.48 cm long. They grow rapidly and often reach adult size in 2 to 3 years. Eastern indigo snake females invest in young through supplying the egg and finding a safe place to lay their eggs. There is no further parental investment. (Murphy, 2003)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

The average lifespan of a wild eastern indigo snake is commonly 17 years. However, they can survive up to 21 years in the wild. The longest living indigo snake lived in captivity for 25 years and 11 months. ("Welcome to Zipcode Zoo", 2009; Stevenson, et al., 2003)

  • Range lifespan
    Status: wild
    12 to 21 years
  • Average lifespan
    Status: wild
    17 years
  • Range lifespan
    Status: captivity
    16 to 25 years
  • Average lifespan
    Status: captivity
    23 years
  • Typical lifespan
    Status: wild
    15 to 21 years
  • Average lifespan
    Status: wild
    17 years
  • Typical lifespan
    Status: captivity
    16 to 25 years
  • Average lifespan
    Status: captivity
    23 years

Behavior

Eastern indigo snakes display a wide range of behaviors. They are active during the day. In summer months they prefer wetland habitats and tend to move to drier habitats in the winter. Unlike many other snakes, eastern indigo snakes breed and are more active in the winter months. Although eastern indigo snakes shift among habitats throughout the year, they don't exhibit true migration. Because they live in warm temperate areas, eastern indigo snakes only hibernate a few weeks out of the year. They may travel as much as 4 miles between foraging and winter retreats. (Ditmars, 1939)

Home Range

Home range sizes of male eastern indigo snakes ranges from 0.72 to 1.9 square kilometers. Adult female indigo snakes usually have home ranges of 0.18 to 0.49 square kilometers. Home ranges generally are largest during the summer and smaller during the winter. ("Environmental & Extension Services - Natural Resources: Florida Eastern Indigo Snake (Drymarchon corais couperi)", 2001)

Communication and Perception

Eastern indigo snake females use pheromones to attract males. Some researchers take advantage of this method of communication to attract males and capture them for research. ("Eastern Indigo Snake: Drymarchon corais couperi", 1999; Ditmars, 1939)

Food Habits

Eastern indigo snakes consume a variety of food sources. They have one of the most varied diets of any snake. Eastern indigo snakes eat mammals, frogs, lizards, fish, eggs, birds, and other snakes, including venomous snakes. Eastern indigo snakes are immune to the venom of sympatric species of venomous snakes. Interestingly, they are one of the only snakes known to eat young turtles. Like other snakes, they typical eat their prey while it is still living. However there has been recorded cases of an eastern indigo snake beating prey against a nearby object to kill it. Eastern indigo snakes do not constrict their prey, they typically overpower it until the prey is exhausted to the point at which it can't escape, sometimes immobilizing the prey by pressing it to the ground. Their powerful jaws are used to grasp and pin down their prey until it can be ingested. ("Eastern Indigo Snake: Drymarchon corais couperi", 1999; "Environmental & Extension Services - Natural Resources: Florida Eastern Indigo Snake (Drymarchon corais couperi)", 2001; "Welcome to Zipcode Zoo", 2009; Stap, 2001)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • fish
  • eggs

Predation

Humans are an important threat to eastern indigo snakes. At adult size they have few natural predators, but smaller or younger snakes may be taken by larger predators, such as large hawks. If eastern indigo snakes are threatened, they will first try to retreat quickly. If retreat is not possible, these snakes will display intimidating behavior when confronted by a potential threat. These behaviors include flattening their heads, hissing, and vibrating their tails. However, they rarely bite humans. Eastern indigo snakes protect themselves by hiding in burrows and by behaving cryptically. Their coloration may also help to protect them somewhat. ("Eastern Indigo Snake: Drymarchon corais couperi", 1999; Smith, 2002)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Eastern indigo snakes occupy abandoned gopher tortoise burrows, where they seek protection and reproduce. After eastern indigo snake young hatch, they may remain in the nest for a day or two before dispersing. Eastern indigo snakes also help control populations of rodents and other snakes, including venomous snakes, in their home range. ("Eastern Indigo Snake: Drymarchon corais couperi", 1999; "Environmental & Extension Services - Natural Resources: Florida Eastern Indigo Snake (Drymarchon corais couperi)", 2001; Smith, 2002)

Mutualist Species

Economic Importance for Humans: Positive

Eastern indigo snakes were commonly used in the pet trade before this became illegal. They were prized in the pet trade for their docile nature and hardiness. Currently, some are bred in captivity as pets but keeping eastern indigo snakes is regulated and permits are required. Now though, to keep an indigo snake in a one's possession one must have a permit or it is illegal. Eastern indigo snakes are important predators of rodents and venomous snakes, which helps to regulate populations of these potentially harmful animals. Eastern indigo snakes are not aggressive and often live near humans without any negative interactions, aside from human persecution resulting from misunderstanding about snakes and their important ecological roles. ("Environmental & Extension Services - Natural Resources: Florida Eastern Indigo Snake (Drymarchon corais couperi)", 2001; Ditmars, 1939; Murphy, 2003)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Eastern indigo snakes are not a threat to humans. Their status as endangered species sometimes interferes with construction projects. ("Environmental & Extension Services - Natural Resources: Florida Eastern Indigo Snake (Drymarchon corais couperi)", 2001; Stevenson, et al., 2003)

Conservation Status

Humans present that greatest threat to eastern indigo snakes. Appropriate habitat is destroyed during roadway and housing construction and logging and agricultural activities. Domesticated animals and pesticides also negatively affect populations. Eastern indigo snakes are sometimes accidentally gassed in their burrows by rattlesnake poachers and they were frequently and illegally taken from their natural habitats and sold as pets. Eastern indigo snakes were placed on the U.S. endangered species list in 1971. Since then, they have been protected by the United States Fish and Wildlife Service and the Florida Fish and Wildlife Conservation Commission. Under this protection, it is illegal to possess, harm or harass eastern indigo snakes and permits are required to keep or transport them. Several adult snakes have been returned to sandhill regions and are being monitored for conservation research purposes. Populations remain threatened. ("Eastern Indigo Snake: Drymarchon corais couperi", 1999; "Environmental & Extension Services - Natural Resources: Florida Eastern Indigo Snake (Drymarchon corais couperi)", 2001; "Welcome to Zipcode Zoo", 2009)

Contributors

Anika Gooch (author), Centre College, Meredith Ranney (author), Centre College, Stephanie Fabritius (editor, instructor), Centre College, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

agricultural

living in landscapes dominated by human agriculture.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

1999. "Eastern Indigo Snake: Drymarchon corais couperi" (On-line). Accessed May 04, 2009 at http://www.fws.gov/verobeach/images/pdfLibrary/eisn.pdf.

2001. "Environmental & Extension Services - Natural Resources: Florida Eastern Indigo Snake (Drymarchon corais couperi)" (On-line). Official web site of the Charlotte County Board of County Commissioners. Accessed May 04, 2009 at http://charlottecountyfl.com/EnvironmentalServices/NaturalResources/indigo.asp.

2009. "Welcome to Zipcode Zoo" (On-line). Accessed April 08, 2009 at http://zipcodezoo.com/Animals/D/Drymarchon_couperi.

Daerr, E. 1999. Eastern Indigo Snakes. National Parks, Vol. 73/ Issue 9/10: 40. Accessed May 04, 2009 at http://web.ebscohost.com/ehost/detail?vid=3&hid=120&sid=93ecf47a-7df6-498d-88f9-533b4dd4d0a4%40sessionmgr103&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=aph&AN=2247358.

Diemer, J., D. Speake. 1983. The Distribution of the Eastern Indigo Snake, Drymarchon corais couperi, in Georgia. Journal of Herpetology, Vol.17/Issue 3: 256-264. Accessed May 04, 2009 at http://www.jstor.org/stable/1563828?&Search=yes&term=snake&term=indigo&term=eastern&list=hide&searchUri=%2Faction%2FdoBasicSearch%3FQuery%3Deastern%2Bindigo%2Bsnake%26gw%3Djtx%26prq%3Dindigo%2Bsnake%26Search%3DSearch%26hp%3D25%26wc%3Don&item=3&ttl=537&returnArticleService=showArticle.

Ditmars, R. 1939. A field book to North American Snakes. New York: Doran & Company.

Murphy, J. 2003. Grzimek's Animal Life Encyclopedia: Reptiles.

Smith, R. 2002. "Eastern Indigo Snakes" (On-line). Accessed May 04, 2009 at http://www.nbbd.com/godo/ef/indigo/index.html.

Stap, D. 2001. Tracking North America's Largest Snake. National Wildlife, Vol 39 / Issue 6: 16. Accessed May 04, 2009 at http://web.ebscohost.com/ehost/detail?vid=3&hid=120&sid=93ecf47a-7df6-498d-88f9-533b4dd4d0a4%40sessionmgr103&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=aph&AN=5397197.

Stevenson, D., K. Dyer, B. Willis-Stevenson. 2003. "SURVEY AND MONITORING OF THE EASTERN INDIGO SNAKE IN GEORGIA."" (On-line). Accessed April 08, 2009 at <http://www.bioone.org/doi/full/10.1656/1528-7092%282003%29002%5B0393%3ASAMOTE%5D2.0.CO%3B2>..

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