Scientists from the University of Mainz and the Senckenberg Museum of Natural History Goerlitz recently described a new slave-making ant species from the eastern USA. They baptized the new ant Temnothorax pilagens since it pillages other ant colonies.

In contrast to the famous slave-hunting Amazon ants whose campaigns may include up to 3,000 warriors, this newly discovered slave-maker is minimalistic in expense, but most effective in result. These tiny ants are only 2.5 millimeters long, and their range is only a few square meters of forest floor.

A slave hunter (below) and a slave (top) in head-to-head contact. Photo by Miriam Papenhagen.

The victims of their raiding parties are societies of two related ant species that live in hollow nuts or acorns. The ants are usually well protected inside the nuts, which have thick walls and a single entrance hole of only 1 millimeter in diameter, so they cannot be entered by larger enemy ants.

An average raiding party of the pillage ant contains just four slave-hunters, including the scout which discovers the targets. Due to their small size, the raiders easily penetrate the slave species nut homes.

The observed behavior is surprising because invading ants and their victims often fight extremely fiercely. However, in several observed raids of the pillage ant, the attacked ants did not defend themselves, and instead allowed the robbers to freely carry away broods and even adult ants to be integrated into the slave workforce. The attacked ants did not show aggression or try to defend themselves because they couldn’t recognize the slave-hunters due to a neutralizing chemical components on the cuticle of the pillage ant, which acts as a sort of chemical camouflage.

The survival of slave ant nests is good for the slave hunters since it provides the chance for further raids in the future, but in other observed raids, the chemical camouflage was less effective -– perhaps because the attacked ant population was strongly imprinted to a more specific blend of surface chemicals.

If slave ants do try to defend themselves, their chances at winning a fight with pillage ants is nearly zero. The attackers use their stingers in a sophisticated way, aiming them precisely in the tiny spot where the slave ant’s neck is soft-skinned. This stinging causes immediate paralysis and quick death and may result in high rates of casualties ranging from 5% to 100% of the attacked nests’ population, with no casualties among the attackers. Since the pillage ants can conduct such successful raids with such few losses, researchers wonder which factors regulate their populations.

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– Temnothorax pilagens sp. n. – a new slave-making species of the tribe Formicoxenini from North America (Hymenoptera, Formicidae)