Army Ant

Army ants are a group of tropical ants best known for their unique nomadic lifestyle. The most familiar New World genus, Eciton, ranges from Mexico through Central and South America, while related but separately evolved lineages of army-ant-like species, such as the driver ants of the genus Dorylus, occupy similar ecological roles in tropical Africa and Asia.

Unlike most ants, army ant colonies do not build a fixed nest. Instead, they alternate between a stationary phase, during which the colony forms a temporary bivouac from the linked bodies of thousands of workers to shelter the queen and brood, and a nomadic phase, during which the entire colony relocates nightly while raiding for prey.

Army ant raids are a dramatic feature of tropical forest ecology, and their columns are often accompanied by "ant-following" birds and other animals that feed on insects flushed out by the advancing ants, illustrating the species' broader role as a keystone predator within its ecosystem.

• Workers are polymorphic, ranging from about 3 mm in minor workers up to 12 mm or more in soldiers
• Soldiers have distinctively large, sickle-shaped mandibles used for defense
• Reddish-brown to blackish body coloring
• Workers are essentially blind, relying on chemical trails rather than vision
• No permanent nest structure is ever visible; look instead for dense marching columns or a temporary bivouac of clustered ants
• Distinguished from other large ants by their massed, highly organized raiding columns rather than solitary foraging

True Eciton army ants are found in the lowland and montane tropical forests of Central and South America, from southern Mexico to Argentina. They are most active in humid rainforest leaf litter and understory, where their nomadic raids and temporary bivouacs can be encountered on the forest floor.

Army ants are specialized predators that hunt cooperatively in massive raiding columns, capturing other insects, spiders, and occasionally small vertebrates disturbed by the advancing swarm. Raids can involve hundreds of thousands of workers moving in a coordinated front. The colony alternates between roughly two-week nomadic phases, during which it raids and relocates nightly, and stationary phases lasting about three weeks, timed to the queen's egg-laying cycle. During the stationary phase, workers link their own bodies together to form a temporary bivouac nest.

Like all ants, army ants undergo complete metamorphosis through egg, larva, pupa, and adult stages, with brood development tightly synchronized to the colony's nomadic and stationary cycle. Colonies are headed by a single, wingless queen who is unable to survive outside the colony and never flies; new colonies form through fission, when part of the colony splits off with a newly produced queen rather than through traditional winged nuptial flights.