- Dorsal scales are smooth (though large adult males may have a couple of keeled rows) and in 17 rows near midbody.
- Anal plate is undivided.
- Indigo snakes are easily identified by their thick, shiny black bodies.
Their dorsal surface color is translucent black or blue-black, from which their common name of "indigo" comes.
Belly scales are also blue-gray.
The head and chin often are reddish or orange brown, with the head also having at times prominent dark lines radiating downward from the eye.
Indigo snakes are typically between (3-8 ft) although they have found measuring over (100 in) and weighing around (5-6 lbs) in weight.
Indigo snakes are found from the southern U.S., through Central America, and in southern South America. Drymarchon melanurus is found from Texas south through Central America to Venezuela. Another species of indigo snake, Drymarchon couperi, is found in Florida and in adjacent Mississippi, Alabama, and Georgia. The third indigo snake species, Drymarchon corais is found only in South America.
Often active in the mornings, indigo snakes are voracious foragers that actively search for anything small enough to swallow, including other large snakes (including rattlesnakes) and birds. In fact, one indigo snake was found to have recently eaten three mice, two small snapping turtles, and two toads. When captured, indigos may bite repeatedly and release foul smelling musk and feces to instigate their release. Indigos may also hiss, vibrate their tail, and flatten their necks vertically to appear "dangerous".
Mating takes place in the winter with eggs laid in the spring. Up to 12 eggs are deposited and the young hatchlings appear about 80 days later, measuring up to 66 cm (26 in) long and possessing more red coloration towards their heads than do the adults.
Indigo snakes are restricted to the riparian areas found in the remaining areas of mesquite savanna and thorn brush woodland left in south Texas. They can be found lying along canal banks or coiled in the lower branches of trees overhanging ponds or streams.
Indigo snakes are listed as threatened by the Texas Parks and Wildlife Department and are protected by the state of Texas.
Drymarchon m. erebennus is found throughout much of the southern third of Texas, found as far north as San Antonio and Del Rio.