Meat ants live in underground nests of over 64,000 ants. Many nests may be connected together into a supercolony that stretches up to 650 m (2,130 ft). Nest holes are regularly arranged, and each leads to a separate series of branched tunnels, which typically do not connect with the tunnels from other holes. Satellite colonies are commonly formed by reproductively active daughter queens near the main nest, usually around 5-10 m away, or sometimes as much as 50 m.
The use of different parts of the nests is largely dependent on environmental factors; for example, excessive shading of the main mound will stimulate the occupation of different parts of the nest or the expansion of satellite colonies. Meat ants cover their nest mounds with gravel, sand, leaf petioles, twigs, seed capsules, mollusk shells, and other small items, which heat the nest more quickly in the morning.
Meat ants are omnivorous scavengers that get their name from their use, by farmers, to clean carcasses. They are diurnal, but on hot days, foraging is bimodal, with all activity ceasing during the heat of the day.
Like other Iridomyrmex species, they engage in a mutualistic relationship with certain caterpillars and butterflies of specific species which produce secretions on which meat ants will feed. In return, they protect the caterpillars from predation. Honeydew collected from hemipterous insects is the main component of the diet of most meat ant colonies. This is supplemented by scavenging for dead invertebrates.
Meat ants do not have dedicated soldier and worker castes like some ants. Instead, they exhibit age caste polyethism, meaning they take on different roles in the colony at different ages. Young ants care for eggs and larvae in the nest. Older ants form part of large foraging parties to exploit significant stationary food resources, such as a dead animal or a colony of hemipterous insects. Older ants undertake lone foraging across open ground, predominately collecting invertebrates and “building material”. The oldest ants are involved in intercolony competition.
Meat ants exhibit aggressive competitive interaction with other species of ants, so are a dominant component of Australian ant communities. Other species employ strategies to exploit resources or habitats not favoured by meat ants, or forage at alternate times (like the common crepuscular Camponotus species). They are aggressive towards meat ants from neighbouring colonies. Old workers engage in ritual combat along borders between colonies to establish foraging boundaries. Like many other species of ants, meat ants are able to communicate with one another using chemical cues.
Meat ants are able to kill poisonous cane toads, an introduced pest, as the toxins that usually kill a cane toad’s predators do not affect the meat ants. The cane toad’s normal response to attack is to stand still and let their toxin kill the attacker, which allows the ant to attack and eat the toad.