Though researchers have known for a while that ant colonies can live inside fruits, a new study in Nature Plants reveals that this housing arrangement is far more complex and ancient than we knew. University of Munich biologists Guillaume Chomicki and Susanne S. Renner went to Fiji to observe the ants and found that they inhabited six different species of Squamellaria. Each of these species evolved to grow in tree bark using a specialized root system called a foot. When the plants are still young, the ants enter a small cavity in the stalk called a domatium to fertilize it. Though the researchers never directly observed how the ants did the fertilizing, they speculate that basically the ants are pooping in there.
from In Fiji, ants have learned to grow plants to house their massive colonies