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New Insights Into Acacia Ant Conflicts

It has been too long since I've posted here, so let's jump in with two discussions about battles and weaponry in the insect world. Today we'll look at battles among acacia ants. Tomorrow let's take a look at animal weapons in general.

Acacia ants, Crematogaster mimosae, live on and fiercely defend Africa's whistling thorn acacia trees, Acacia drepanolobium.

Crematogaster_mimosae_casent0904507_p_1_highCrematogaster mimosae photograph by Will Ericson / © AntWeb.orgCC-BY-SA-3.0

Scientists have found they can induce battles between ant colonies on separate trees by bringing the branches of the trees into contact. The worker ants begin to fiercely defend their home tree when overlap occurs. The ants both bite and release a venom. When in defensive mode, Crematogaster ants hold their metasomas over their backs in a characteristic way, which has given them the common name "acrobat ants." Unlike some ants that have more ritualistic confrontations, Acacia ants actually battle causing significant losses in the number of workers. Before one colony is completely wiped out, however, the battle ceases and one colony is the apparent winner.

Recently Kathleen P. Rudolph and Jay P. McEntee studied Crematogaster mimosae colony battles in Kenya. They examined the genetic makeup of workers of the colony before and after the battles and discovered the winning colony became more genetically diverse afterwards. In other words, worker ants from the losing colony were joining forces with those of the winning colony. In fact, when two colonies fought to a draw, they actually ended up fusing together, including their queens.

From an ant biology conventional wisdom, this is startling finding because it is generally thought ant colonies reject workers that are not their sisters. However, the fact that even the winning colony is weakened and can't defend the trees against large herbivores makes the ability to recruit workers from a losing colony a distinct advantage.

Of course, there are ants that raid other colonies for pupae. Other ants eat the bodies of their fallen victims. Do you know of any other ant species that recruit or allow the losing workers to join the colony?

Literature:

Kathleen P. Rudolph, Jay P. McEntee. Spoils of war and peace: enemy adoption and queen-right colony fusion follow costly intraspecific conflict in acacia ants. Behavioral Ecology, 2015

Mack, Aileen. "Turn mortal enemies into allies? Ants can. UF News. 17 March 2016. .

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