The question of whether red ants and black ants can live together is complicated because “red ants” and “black ants” are common names covering hundreds of different species. The short answer is that permanent cohabitation is nearly impossible. The complex social structure of ants is built on fierce exclusivity, meaning a vast majority of ant species are intensely territorial. They actively compete with any nearby colony, regardless of color, and interactions between different species are typically hostile.
The Biological Basis of Ant Aggression
The primary factor preventing different ant species from coexisting is the highly refined system of colony recognition. Ants distinguish their nestmates from all others through a specialized chemical signature, often referred to as the “colony smell.” This odor is a blend of cuticular hydrocarbons (CHCs), which are waxy compounds on the ant’s exoskeleton that function as a chemical identification badge. Each ant colony possesses a unique ratio of these hydrocarbons, determined by both genetics and environmental factors like diet. The presence of foreign CHCs acts as a trigger for aggression, instantly identifying an intruder as a threat. Unless the foreign ant can chemically mimic the colony’s scent, it will be met with hostility. This recognition system is closely tied to genetic relatedness; ants are far less aggressive toward non-nestmates who share a closer genetic signature. Any ant from a different species is immediately identified as a competitor or a predator, leading to fierce defense of resources and nesting sites.
Types of Inter-Colony Conflict
When different species of ants meet, the interaction is rarely passive and often escalates into distinct forms of conflict. These aggressive encounters are primarily driven by the need to eliminate competition for limited resources or to acquire protein. The outcome of these battles depends on the relative colony sizes and the specific adaptations of the species involved.
Direct Warfare
Direct warfare occurs when two colonies, often of similar size and competitive ability, engage in large-scale battles over disputed territory. A classic example involves the red imported fire ant (Solenopsis invicta) and the black Argentine ant (Linepithema humile), both highly invasive species. Fire ants utilize their powerful sting and venom, while Argentine ants rely on superior numbers and recruitment capabilities to overwhelm their opponent. In lab experiments, a large colony of Solenopsis invicta workers was observed to invade the Argentine ant nest and eliminate the rival queens and brood. Conversely, smaller fire ant colonies are easily overwhelmed by larger Argentine ant populations, which may even raid the fire ant’s nest and remove their brood. Battles also feature black ants, such as some Formica species, spraying formic acid, a chemical deterrent that can dissolve the exoskeleton of their opponents.
Predation
Predation occurs when one species actively hunts the workers and brood of another for food. Red ants, like the Big-Headed Ant (Pheidole megacephala), may actively prey on the red imported fire ant (Solenopsis invicta) workers. The black Pheidole minors and soldiers work together to subdue the fire ant. Multiple minor workers “spread-eagling” the larger Solenopsis worker to immobilize it before a soldier can deliver a fatal blow. This predatory behavior provides the attacking colony with a valuable source of protein. Such raids often result in the retrieval of dismembered opponent body parts and the theft of the rival colony’s pupae and larvae, which are consumed to support the growth of the aggressor’s colony. The ability of one species to overcome another is a significant factor in local species displacement.
Resource Raiding
Resource raiding involves fighting specifically over a highly concentrated or desirable food source, such as a dead insect or a patch of honeydew. A skirmish may break out the moment a red ant and a black ant meet near a shared resource, with each trying to drive the other away. The speed of recruitment, where one ant quickly alerts nestmates to the presence of the resource and the competitor, often determines the victor. These clashes are driven by the immediate need for sustenance. Colonies with faster-moving workers or a more effective alarm pheromone system often secure the resource and force rivals to retreat. This low-level competition constantly shapes the foraging patterns and territory boundaries of neighboring ant colonies.
Temporary Cohabitation and Symbiotic Exceptions
While permanent, peaceful cohabitation is rare, a few exceptions exist where different ant species may share space, though the relationship is often one of exploitation.
Social Parasitism (Dulosis)
One complex exception is social parasitism, also known as dulosis or “slave-making.” In this scenario, workers from a dulotic species, such as some red Formica ants, raid the nests of another species, often a black ant like Formica fusca or Formica subsericea, and steal the brood (pupae). The captured pupae hatch within the slave-maker’s nest and imprint on the new colony’s scent, believing they are home. These “slave” workers then perform all the necessary colony duties, including foraging, nest maintenance, and caring for the parasitic queen’s young. The slave-maker workers focus only on defense and raiding. This arrangement is obligatory for some slave-maker species, which cannot survive without the labor of the captured workers.
Shared Resource Foraging
A less dramatic form of temporary sharing occurs when two different species are drawn to a large, abundant resource, such as a honeydew-producing aphid colony. In this situation, the cost of fighting a full-scale battle may temporarily outweigh the benefit of monopolizing the food source. The ants may forage in proximity, maintaining a tense distance, as long as the resource is plentiful and the immediate threat of colony invasion is absent. However, this proximity is unstable. Minor territorial disputes can quickly erupt into violence if the resource becomes scarce or if an ant wanders too close to a rival nest entrance.