Ants are famous for their regimented and complex social behaviors. In the tropics, they are also famous for forming mutualisms with plants. Certain species of trees have conspicuous hollow swellings that house ants, often feeding the ants with specialized ant food. In return, the ants are pugnacious bodyguards, swarming out to aggressively defend the plant against enemies. Scientists have observed these mutualisms for centuries, but an enduring question is how these intriguing interactions evolved in the first place.
