Slave-making ants or slaver ants are brood parasites that capture broods of other ant species to increase the worker force of their colony. After emerging in the slave-maker nest, slave workers work as if they were in their own colony, while parasite workers only concentrate on replenishing the labor force from neighboring host nests, a process called slave raiding.
The slave-making ants are specialized to parasitize a single species or a group of related species, and they are often close relatives to their hosts, which is typical for social parasites. The slave-makers may either be permanent social parasites (thus depending on enslaved ants throughout their whole lives) or facultative slave-makers. The behavior is unusual among ants but has evolved several times independently.
Terminology
Theft of brood for the purpose of employing the stolen individual's efforts in support of the thief is called dulosis (from Greek , "slave"), but the term "slave-making" is used in older literature and is still common. There is some controversy associated with using the term "slave" and "slave-maker" to describe the natural history of this species. Additionally, there are species commonly raided that are referred to as "negro ant" specifically because they are common victims of ant raids, although this is not endorsed by nomenclature societies. Using this terminology can cause discomfort and negativity such that it may discourage certain people from wanting to study these ant behaviors. Some have argued that using such non-inclusive metaphors in science is harmful to scientists and interferes with the unbiased scientific process. Suggestions to replace these terms with alternatives include replacing "slave-making ant" with "pirate ant" or "kidnapper ant" and replacing "slave" with "captive".
A related type of social parasitism is called inquilinism, in which a reproductive enters a host colony, lays eggs, and relies on the host colony to rear its offspring. Unlike brood parasitism, the inquiline remains within the nest and typically its brood does not outnumber the host's brood.
Obligate and facultative slave-makers
Slave-making ants may be permanent social parasites, thus depending on enslaved host ants throughout their whole lives and unable to function without them in which case they are termed obligate slave-makers. Alternatively, facultative slave-making ants, like those in the Formica sanguinea complex, represent an intermediate parasitic group, between free-living species and obligatory slave-making species. In laboratory tests, when captured workers were removed from colonies of Formica sanguinea and Polyergus rufescens, the behavior of F. sanguinea changed dramatically within 30 days of their removal, with workers becoming self-sufficient at feeding and brood care. Workers of Polyergus, in contrast, were unable to care for their brood, and experienced high mortality.
Raids
Parasitized nests need to replenish the host workers periodically. This is achieved by raiding other nests in a process called slave raiding. The parasite workers are specialized for conducting raids in a two-step process. First, scouts individually search for potential host nests. When successful, the scout returns to its nest and recruits nest-mates to initiate the raid, during which slave-maker ants seize a brood and bring it back home. A colony may capture 14,000 pupae in a single season. Most slave-raiders capture only the young, but Strongylognathus sp. also enslave adult workers.
In most parasite species, workers mark the way to their nest with pheromones and afterwards fellow slave-makers are attracted within a few seconds. They then go quickly to the targeted host nest, attack it, and carrying as many larvae and pupae as possible, return to their nest following the same trail marked by the pheromone. Rossomyrmex is the only reported slave-maker that exclusively uses adult transport and single recruitment chain instead of pheromones during raids, a behavior probably constrained by the arid habitat; raids take place in early summer when soil surface temperature can reach up to , a temperature in which pheromones would quickly evaporate.