Naked mole-rats (Heterocephalus glaber) have long been considered friendly animals, being one of the few mammalian species to live in eusocial colonies. Their life is comparable to that of bees, existing within tight-knit colonies made up of sterile workers and a single reproducing queen. New research published in the Journal of Zoology, however, has highlighted the less-than-friendly behaviors that can occur between colonies, as it was found that wild colonies have invaded their neighbors and even kidnapped their pups.

Led by Stan Braude at Washington University, researchers first noted the Viking-esque behavior back in the early 90s, but without sufficient genetic technology to corroborate their observations they were unable to confirm their findings. These early observations came as part of a study looking at naked mole rats in Meru National Park, Kenya, where they suspected 26 colonies had expanded their territory by colonizing neighboring nests. To investigate their theory, they captured and marked entire colonies to see where they ended up as the researchers returned year after year.

Four years on, the team noticed that a queen had injuries to her face. Loyal workers would never attack their precious queen and therefore the researchers suspected the wounds were indicators that a second colony had attacked the nest. Having marked rats from both colonies, the researchers returned the next year to find that two pups from the injured queen’s colony were now living as worker rats in the invading colony’s nest. Perplexed by their findings, the team initially put the unusual observation down to human error when tagging the animals.

Thankfully, as time ticked on so too did technological advancements, and now with an arsenal of genetic analyses at their disposal, the same team have been able to confirm from tissue samples that the pups really had been kidnapped from a different colony. The hostages by this stage had become completely integrated into their adopted colony as workers, drawing parallels between these mammals and slave-making ants, brood parasites who steal the young of other ant species as a means of increasing the workforce.

The researchers state their findings support reports of inter?colony aggression and invasion seen in laboratory colonies and indicate that direct aggressive competition for resources may act as a driving force for the large colony size in naked mole?rats. Their results also confirm that invading colonies may kidnap un?weaned pups to be integrated into their workforce. Not so friendly after all, it seems.