The question of whether ants have “slaves” is a biological reality, though the term carries complexities. Scientists refer to this unique form of social parasitism as dulosis, which translates from Greek to “enslavement.” This behavior, found in several genera of ants, is a highly specialized evolutionary adaptation where one species exploits the labor force of another.
Defining Dulosis: The Biological Reality of “Slave-Making”
Dulosis describes a form of permanent social parasitism where one ant species, the slave-maker, raids the nest of another species, the host, to steal its young. Slave-maker species, such as the Amazon ants (Polyergus species), are often so specialized for raiding that they have lost the ability to perform basic colony maintenance tasks. The host species is typically a closely related, non-parasitic ant, frequently belonging to the Formica genus.
The degree of dependency varies across dulotic species, ranging from facultative to obligate. Facultative slave-makers, like Formica sanguinea, can function without captives but are more productive with them. Obligate slave-makers, such as Polyergus rufescens, are entirely dependent on their captives to survive, as their own workers are specialized for combat and raiding. Without the captured workers, the slave-makers cannot feed themselves or raise their own young.
The Mechanics of the Raid
The process of acquiring new workers begins with a scout ant from the slave-maker colony locating a nearby host nest. Once a suitable target is found, the scout returns to its colony and recruits a large raiding army, communicating the path via chemical trail pheromones. These specialized workers, which are adapted for fighting, then march toward the victim colony in a highly organized column.
Upon reaching the host nest, the raiders release specific chemicals, known as propaganda pheromones, to subdue the defending ants. These substances trigger confusion and panic in the host workers, causing them to scatter and flee the nest instead of mounting an effective defense. This disarray allows the slave-makers to enter the nest relatively unopposed and seize the host colony’s pupae and larvae. They then transport the stolen brood back to their own nest; a single colony may steal thousands of pupae in a single season to maintain its workforce.
Life in the New Colony: Roles of the Captive Ants
Once the stolen brood is brought back to the slave-maker nest, the host ants emerge in the parasitic nest and imprint on the new colony’s unique odor. The newly emerged workers subsequently integrate themselves into the parasitic colony, performing the full range of duties that the slave-maker workers are incapable of performing.
The captive ants are responsible for foraging for food, maintaining the cleanliness of the nest, and feeding both the slave-maker queen and the parasitic brood. They even groom the slave-maker workers. In some cases, the enslaved workers will also participate in the defense of the mixed colony, actively protecting the nest and the parasite’s brood from intruders. This arrangement creates a functional colony where the slave-makers focus solely on reproduction and replenishing their workforce, while the captives provide all necessary labor.
Evolutionary Reasons for this Specialized Behavior
Dulosis is an extreme example of evolutionary specialization. The behavior likely arose from a predatory ancestor that occasionally stole brood. Over time, the selective pressure to maximize raiding efficiency led to a corresponding loss of basic worker functions in the parasitic species, making them obligate parasites.
This parasitic strategy allows the slave-maker colony to conserve the energy and resources that would otherwise be spent on foraging, nest construction, and brood care. The life of the captive ants, while seemingly altruistic to a non-related species, is a consequence of their early olfactory imprinting and the parasite’s exploitation of their innate worker behavior.