Every summer, blood-red ants of the species Formica sanguinea go on a mission to capture slaves. They infiltrate the nest of another ant species, like the peaceful F. fusca, assassinate the queen, and kidnap the pupae to raise as the next generation of slaves. Once the slaves hatch in their new nest, they appear none the wiser to their abduction, dutifully gathering food and defending the colony as if it were their own.
Scientists have long wondered how such slavemaking behavior evolved. Now, new evidence suggests that today’s slave snatchers started out as temporary parasites—ants that laid their eggs in the nests of other species and then used those workers as part-time caregivers for their own offspring.
The evolution of enslavement in Formica ants has long eluded scientists, largely because they didn’t know how species in the genus were related. So Jonathan Romiguier, a molecular biologist at the University of Lausanne in Switzerland, and colleagues sequenced and meticulously mapped the genetic relationships of 15 Formica species to create the most robust family tree to date. The tree includes major branches for slavemakers, species without slaves, and parasitic species that exploit foreign workers on a temporary basis.
