The dulotic ant Polyergus rufescens raids the nests of other ant species and steals their pupae. When these pupae hatch in the raider's colony, they imprint on their captors and perform all the colony's work—the Polyergus ants cannot even feed themselves without their captive workforce.
Ants That Kidnap Other Ants to Do All Their Work
Imagine being so specialized that you literally cannot feed yourself. That's the evolutionary path chosen by Polyergus rufescens, commonly known as slave-maker ants or dulotic ants. These remarkable insects have evolved to depend entirely on kidnapped workers from other species.
The Raid
On a summer afternoon, scout ants from a Polyergus colony venture out to find target nests—usually colonies of Formica ants. The scouts evaluate potential targets carefully: larger nests with more brood get priority. A nest with insufficient workers? Not worth the effort. Once a suitable target is identified, the scout returns home and recruits raiders.
The raiding party—sometimes hundreds strong—marches in formation to the target nest. What follows is swift and brutal. The raiders storm in, using their sickle-shaped mandibles to fight off defenders. But they're not there to kill. They're there to steal babies.
The raiders grab pupae and larvae, carrying them back home. A successful colony might capture 14,000 pupae in a single season. These aren't random kidnappings—this is how Polyergus colonies survive.
The Psychology of Capture
Here's where it gets fascinating: the captured pupae don't "know" they've been kidnapped. When they emerge as adult ants in the Polyergus nest, they imprint on their surroundings. They treat their captors as nestmates and perform all the tasks a normal ant would do: foraging, feeding larvae, maintaining the nest, and even feeding the Polyergus ants who kidnapped them.
The Polyergus ants, meanwhile, have become so specialized for raiding that they've lost the ability to do basic tasks. Their mandibles are shaped like curved daggers—perfect for fighting, terrible for carrying food or caring for young. Without their captive workforce, a Polyergus colony would starve within days.
An Evolutionary Dead End?
This lifestyle comes with risks. Polyergus colonies depend entirely on:
- Finding enough nearby Formica nests to raid
- Successfully overwhelming defenders during raids
- Capturing sufficient pupae to maintain workforce levels
- The captive ants accepting their role without rebellion
Some researchers have observed behavioral plasticity in the system. When Formica cinerea are the captive workers, the Polyergus raiders sometimes drop pupae at the nest entrance, allowing the Formica workers to retrieve them. It's unclear if this is learned behavior or genetic adaptation.
Scientists call this social parasitism—a fascinating evolutionary strategy where one species exploits the social behavior of another. And while the terminology of "slave-making" has ethical weight when applied to insects with no concept of freedom, it does capture the bizarre reality: these ants have evolved to build their entire society on the labor of kidnapped workers from another species.
