Where an ant goes when it’s gotta go

Most of us think ants are unsanitary; it certainly seems that way when they’ve invaded our homes. But scientists have spotted ant behaviors that show that the insects are cleaner than you might think. Some ant species are known to form “kitchen middens” outside their nests, full of waste and fecal material. And in some species of leaf-cutting ants, only specialist waste management workers go into refuse chambers.

Black garden ants (Lasius niger), a common species in Europe, make those refuse piles outside their nests, filling them with food remains, corpses of dead nest-mates and other refuse. But Tomer Czaczkes and colleagues at the University of Regensburg in Germany spotted distinct, dark patches within the nests of ants in the lab. The team thought the patches might be where ants were depositing fecal matter but had to set up an experiment to test the idea. Their study was published February 18 in PLOS ONE.

The researchers constructed 21 plaster nests in the lab, each with a group of 150 to 300 ants living inslde. They then fed the ants a sugar solution laced with one color (red or blue) and a protein food laced with the other color. Once a week for two months, the nests were photographed, and a person who was unfamiliar with the experiment recorded the locations of dark patches in the nests and what color those patches were.

Every nest had at least one dark patch, and some had as many as four. The patches were always the same color as the sugar solution and were mostly in the nest corners. The patches never contained nest debris, dead ants or colored bits of the protein food source — those were all relegated to the garbage dump outside the nest. And the ants formed those patches whether there were lots of ants in the nest or not.

“The presence of distinct colored patches in the ant nests thus strongly suggests that the ants were defecating in a specific location in the nest,” the researchers write. “We … feel justified in terming these patches ‘toilets.’”

This is the first time that anyone has formally reported finding ant toilets, though other researchers have seen similar structures in the nests of desert ants (Crematogaster smithi). And it’s not quite clear why the ants defecate inside the nests instead of outside. Many species take their business away from their homes to avoid spreading diseases that might be associated with feces. Honeybees, for instance, make special “defecation flights.” But other insects have found feces to be useful as an antibiotic or fertilizer. For the black garden ants, there might be a benefit to keeping their business in house — the toilets might be a source of salt or micronutrients, the researchers suggest. But if future research finds that the ant toilets are prone to carry disease, these insects might want to consider building outhouses.

Editor’s note: This post was updated with a new image of a black garden ant on February 24, 2015.