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Colonies of turtle ants behave as if they are playing a game of Risk. They spread out their forces to control more resources, but also retreat if their position is not defensible.

“They’re sensitive to changes in the environment. They can change the allocation of their defenses in response to that,” says at Harvey Mudd College in California.

is a species of that lives in trees in the Sonoran Desert of Mexico and Arizona. Each colony can hold a few hundred ants, spread out over several nests in tree cavities.

The nests are defended…