Army ants, belonging to the subfamily Dorylinae, are defined by their unique, nomadic lifestyle and their massive, aggressive swarm raids. Unlike many other ant species, these colonies do not build permanent nests, instead forming a temporary “bivouac” composed entirely of their own bodies to house the queen and brood. Their foraging is characterized by a collective hunting strategy known as mass foraging, where millions of workers advance across the forest floor, overwhelming any arthropod in their path. This sheer strength in numbers, combined with the powerful mandibles of specialized soldier ants, makes the entire colony a highly mobile and difficult target for most predators.
Avian Specialists That Follow the Swarm
The most famous associates of army ant raids are the specialized bird species that exploit the chaos of the advancing column. These “ant-following” birds include various antbirds, antthrushes, and woodcreepers, some of which are obligate followers, relying almost entirely on the ants for their diet. The birds do not typically consume the army ants themselves, which are unpalatable, but rather feed on the secondary prey flushed out by the ants.
The ants act as natural beaters, driving arthropods and small vertebrates out of the leaf litter and into the waiting beaks of the birds. This unique relationship is most commonly observed with the Neotropical species Eciton burchellii, which conducts large, diurnal surface raids. Over 50 species of birds have been recorded attending these swarms, creating a feeding spectacle just ahead of the ant front.
This avian association is generally considered parasitic or commensal, as the birds benefit significantly without providing any clear advantage to the ants. Studies suggest that the presence of ant-following birds can actually reduce the ants’ foraging success by up to 30 percent, as the birds snatch larger prey items the ants would otherwise capture. Obligate species, such as the Bicolored Antbird, have evolved such a dependence on this food source that they must constantly track the nomadic ant colony to survive.
Arthropod Parasites and Micro-Predators
Despite the swarm’s formidable defenses, the colony is susceptible to specialized arthropod threats that attack individual ants or infiltrate the bivouac. One method of attack involves certain Phorid flies, minute parasitoids sometimes called “decapitating flies.” The female fly lays an egg on a foraging ant, often in the head or thorax, which eventually causes the ant’s head to fall off as the larva develops inside.
Other threats involve specialized rove beetles (family Staphylinidae). Species like Ecitomorpha and Ecitophya have evolved remarkable chemical and morphological mimicry to integrate seamlessly into the bivouac. These beetles physically resemble the host ants and chemically coat themselves in the ants’ cuticular hydrocarbons, effectively smelling like a nestmate to avoid detection.
Once accepted into the bivouac, these parasitic beetles feed on the colony’s resources, including the ant brood and raided food. This chemical camouflage allows them to live among the aggressive workers, exploiting the colony’s energy investment from within. Other tiny invertebrates, including specialized mites, also infiltrate the bivouac, often attaching themselves to the ants for transport or feeding on the refuse piles.
Terrestrial Vertebrate Interceptors
Ground-dwelling vertebrates preying on army ants must employ strategies of speed, armor, or targeted predation at the swarm’s edges. Fast-moving lizards, such as Ameiva (Amazon racerunners), snatch individual ants straying from the main column or consume insects fleeing the raid. These lizards use their speed and quick reflexes to intercept prey without becoming overwhelmed by the mass of soldiers.
Amphibians, including toads and frogs, opportunistically feed on army ants, relying on sticky tongues to capture individuals quickly. While many frogs eat ants, the high concentration of aggressive army ant workers limits all but the most specialized or quick-feeding predators.
Mammals specializing in eating ants, such as the Giant Anteater or Southern Tamandua, generally avoid confronting a mobile army ant swarm. These animals prefer to target stationary nests of other ant or termite species, performing a quick, concentrated feeding burst before the colony can fully mobilize its defense. The aggressive biting and chemical defenses of the army ant bivouac often make them an unprofitable and dangerous meal for these larger insectivores.