The invaders put on a disguise and infiltrate the nest with dark plans: to kill the queen and enslave the kingdom.

Usually when ants take pupae from other colonies as future slaves all hell breaks loose in ensuing battles. The enslaved individuals sometimes even strike back against their overlords.

It’s a relatively dramatic affair, usually resulting in the aggressive slave-makers carrying the pupae back to their own colony, says Terrence McGlynn at California State University.


But a species of ant found in the eastern US, Temnothorax pilagens, does things differently. It is the first ant species known to waltz into a colony and enslave others without killing, and one of a few that take not only pupae but adult workers, too.

“This was extremely surprising as ants are usually able to detect foreign species or even individuals from a different colony through their chemical profile and react aggressively towards them,” says Isabelle Kleeberg at Johannes Gutenberg-Universität Mainz, Germany, whose team has found how they get away with it.

Kleeberg tracked the behaviour of T. pilagens and their preferred slave species, Temnothorax ambiguus, in 43 raiding experiments using colour-marked individuals. In each experiment the colonies of these two ant species, each housed in a plastic box, were placed 12 centimetres apart from each other.

Easy infiltration

In the majority of cases the raiding went smoothly. Instead of attacking the intruders, the T. ambiguus workers touched them with their antenna or even groomed them, Kleeberg says.

Faced with no opposition, the pillaging ants then used their mandibles to place each T. ambiguus worker on their back and carried them into their own colony. There the enslaved ants were accepted by already established slaves and started work raising the slave-maker brood. When the slave-makers were done transporting all the workers, they came for the brood, Kleeberg says.

The intruders’ secret? Chemical mimicry. After comparing the chemical profile of each species Kleeberg found similarities between both. They share 35 out of the 36 hydrocarbons found on their cuticles, for example.

During the raid, the raiding ants also regularly groomed slaves-to-be or rubbed their body against them to acquire their scent, presumably helping them to avoid recognition, Kleeberg says.

“The slave-maker enters host colonies, trying to be nice and kind, pretending to be one of them, hiding beneath a costume to get accepted,” says Kleeberg.

“The use of this subterfuge in slave-making raids is new,” say McGlynn.

Arms race

Such similarity in scent may be partly explained by the close relatedness of these two species, says Kleeberg. Also, it may reflect an ongoing co-evolutionary arms race, where T. pilagens is currently winning the race. “It seems that [T. ambiguus] has as yet no time to develop defence strategies, such as a more sophisticated recognition ability,” she says.

But they may be on their way to doing so. In about a quarter of raids T. ambiguus individuals tried to escape, fleeing from their attackers by relocating their colony. This suggests they had recognised the intruder.

Fighting back was futile, though. In the few cases where a host colony rebelled, the consequences were dire.

“Pillage slave-makers freaked out and used their efficient stinger to stab their attackers at a squishy spot between their head and thorax. Their victims are paralysed and frequently die,” Kleeberg says.

Journal reference: Behavioral Ecology and Sociobiology, DOI: 10.1007/s00265-015-2018-6

Read more: “Goodwill hunting: Random ants of kindness”

Image information: Temnothorax pilagens being fed by a Temnothorax ambiguus slave (Credit: Isabelle Kleeberg)