Army ant

Army ants hunt for insects and spiders.

They work as a team to catch their food. Then they carry it back to their camp to feed the babies.

Army ants are hunters. A colony spreads out across the forest floor in a wide swarm and catches the insects, spiders and other small animals that it finds, especially the young of other ants and wasps, cockroaches and crickets.

Workers team up to carry big pieces of food home, with large workers as porters. The ants cannot cut well with their pointed jaws, so food that is too big to carry or pull apart is left behind. All of it goes to feed the colony and its growing young.

Swarms take a broad range of prey, including other social Hymenoptera (especially ants), cockroaches and mantids, spiders, scorpions and Orthoptera, while some well-armored arthropods are ignored (AntWiki). Franks (1987) found wasp and ant brood dominating wet-season prey, and cockroaches and crickets in the dry season (Animal Diversity Web).

Prey is subdued by stinging and by pulling off legs and antennae with gripping mandibles. Teams of workers led by large medias carry big items, which Franks (1986) showed is more energy-efficient than cutting prey up. Schneirla reported that snakes, lizards and nestling birds were occasionally killed, but the ants' mandibles lack a cutting edge, so they cannot tear such animals apart. The brood's high-fat diet drives the colony's daily raids during the migratory phase.

At night, army ants hold on to each other in a big, round ball.

This living camp keeps the queen and the babies safe. In the daytime, birds follow the ants to catch bugs that jump out of the way.

Army ants do not dig a nest. Instead, thousands of workers hook their legs together into chains and nets until they form a living ball, called a bivouac, that can be a meter across. The queen and young stay safe inside. They often camp between the roots of big trees or under fallen logs.

At dawn the ball melts away, and the hunting swarm spreads out. It can be 15 meters wide. Many birds, called antbirds, follow the swarm and catch the insects that jump away from the ants. Butterflies come too, to feed on the birds' droppings.

Bivouacs form between tree buttresses, under fallen trunks or up to 20 meters or more up trees; interlocked workers make a mass up to a meter across around the queen and brood. When light exceeds about 0.5 lux, it dissolves into a raid that advances leaderless, up to 20 meters an hour, as front-runners lay trail and fall back (Hölldobler and Wilson 1990). At its height, Schneirla described a front of 15 meters or more, 1 to 2 meters deep. Raids are largely diurnal (AntWiki).

On Barro Colorado Island, Panama, at least ten antbird species follow E. burchellii and Labidus praedator swarms but ignore column-raiding Eciton. Ithomiine butterflies feed on the antbirds' droppings. Euxenister beetles and mites live in the bivouac (Animal Diversity Web).

Army ants need big, shady forests.

The colony walks to new places all the time. Shady paths of trees help them get from one forest to the next.

Army ants have not been given a conservation status. But scientists are watching how they cope when forests are cut into smaller pieces. Because queens cannot fly, a colony can only walk to new places, and hot, open fields block its way.

Studies in Costa Rica and Panama found that cleared land acts like a wall for these ants, while shady strips of forest let them pass. Scientists recommend keeping forests connected. Army ants matter to many other animals, from antbirds to beetles that travel with the colony.

Eciton burchellii has no IUCN Red List assessment (Not Evaluated), and the Animal Diversity Web lists no special status. Because queens are wingless and colonies move on foot, gene flow through females depends on walking routes. Pérez-Espona and colleagues (2012) found deforested areas to be strong barriers to gene flow in Panama, with mature forest promoting it; Soare and colleagues (2014) found that forest clearing impeded queen dispersal in a montane population and recommended maintaining habitat connectivity for this keystone species.

Berghoff and colleagues (2008) found that flying males maintain gene flow between forest patches in the Panama Canal area, with no sign of inbreeding on Barro Colorado Island. Meisel (2006) concluded that shaded vegetative corridors allow colonies to move between fragments and should be preserved. The Animal Diversity Web notes the species' painful sting but says it rarely meets people.