Drymarchon couperi reaches two and a half metres or more, longer than any other snake native to the United States. It hunts by day across large home ranges, taking frogs, lizards, small mammals, birds and other snakes, including venomous ones, which it overpowers with its jaws rather than by constriction.
Its weak point is winter. In the northern part of the range indigo snakes need a frost-free refuge, and the burrows excavated by gopher tortoises in longleaf pine sandhill provide it. Those burrows can run several metres deep and are used by hundreds of other species, making the tortoise a keystone of the ecosystem. As longleaf pine has been reduced to a small fraction of its original extent and tortoise numbers have fallen, indigo snake numbers have fallen with them.
The snake is listed as Threatened under the United States Endangered Species Act, and reintroduction projects in Alabama and Florida have released captive-bred animals into protected longleaf habitat. Its global IUCN assessment differs from that federal listing, which is a common and often confusing mismatch between the two systems.