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Army ants can also make new friends, study shows

In times of need, a colony of army ants will assimilate itself into another colony

A recent study shows that aggressive colonies of army ants can be cooperative when they have to. If the queen of one colony dies, the colony will attempt to assimilate itself into another.

This is according to new research by Daniel Kronauer of the Harvard Museum of Comparative Zoology, Caspar Schöning formerly of the University of Copenhagen, and colleagues Patrizia d’Ettorre and Jacobus Jan Boomsma of the Department of Biology at the University of Copenhagen, as reported in the Harvard Gazette.

The researchers have thereby shed light on the ants’ softer side. The colonies of army ants are otherwise known for their hostility towards each other – they practise a strict border control, keeping off rival soldiers, and making sure that the colonies are kept separate.

A clear pattern

The colonies of army ants are ruled by a queen, who produces millions of eggs. Colonies disappear shortly after the death of a queen, and until recently it was not known what happened to the orphaned ants in the queen-less colony.

The research conducted on the slopes of Mount Kenya in eastern Africa, showed that instead of being killed by a neighbouring colony, the worker ants of a colony that have lost their queen are allowed to join up and fuse into their colony.

Over two field seasons, Kronauer and his team removed the queens of 10 army ant colonies to observe the results. Although they lost two of the colonies, the remaining eight showed a clear pattern.

The odd one out

Seven out of the 10 colonies joined a neighbouring colony, based on genetic analyses. The workers slowly lost the odour of their old colony, and were fully integrated within days.

One of the 10 colonies produced a tiny brood of winged males, with the intention of flying off to find a new queen. This effectively means one last chance at reproducing.

»It is a last option to get some fitness returns before they die,« said Kronauer to the newspaper the Harvard Gazette.

The teams’ findings have been published in The Proceedings of the Royal Society. You need to sign up on their site to read the publication itself, but you can read the abstract here.