Lennart Tange via Wikimedia Commons // CC By 2.0

We might write bugs off as dumb, dirty little creatures, but social insects that live in large groups have come up with plenty of ways to keep their homes clean and sanitary. While ant nests and bee hives don’t have anything as impressive as indoor plumbing and trash compactors, the animals have their own ways of managing waste. Honey bees, for example, go on “defecation flights” to deposit their feces far from the hive. Many ant species make refuse piles called “kitchen middens” outside their nests for dumping bodily waste, trash, and the bodies of dead nestmates. Some ants even have specialized groups of sanitation workers that deal with these piles. Termites go even further and put their feces to work, using it as building material. 

Now German researchers have uncovered another way that insects deal with their poo. For the first time, they’ve found that one species of ant maintains underground “bathrooms” in its nests.

Tomer Czaczkes, a biologist at Germany’s University of Regensburg, has been working with ants for years, studying their behavior and decisions as individuals and colonies, and keeps several white plaster nests of black garden ants (Lasius niger) in his lab for experiments. Over time, he noticed that distinct dark patches always formed in some chambers in the corners of these nests. He suspected that these might be piles of feces—or, in the parlance of ant researchers, frass—and to make sure, he did a little experiment. 

One Poo, Two Poo, Red Poo, Blue Poo

Working with Jürgen Heinze and Joachim Ruther, Czaczkes began feeding ants in 21 different nests a sugar solution colored with food dye. Some nests got a red solution and others got blue. Then, as the ants went about their business and did their business, the scientists watched and waited. After two months, every nest had two to four dark patches in its corners, each the same color as the dye the ants in the nest had been eating. The ants were indeed relieving themselves in specific spots. On closer inspection, the researchers saw that the patches never contained uneaten food, corpses, or other waste, which were dumped outside the nest by all the colonies. The indoor piles were strictly for frass, and the researchers say in their new paper that they “thus feel justified in terming these patches ‘toilets.’”

Why, Czaczkes then wondered, would the ants bother having special chambers as toilets when other insects go to great lengths to get their waste out of their homes? Even these ants took their non-frass waste outside. While the toilets were always tucked away in the corners of the nests, the ants didn’t avoid these chambers and visited them repeatedly, so cleanliness and pathogens that might be in the feces didn't appear to be a concern. And having a kitchen midden outside of the nest entrance seems to rule out the notion that the ants don’t want to take the trouble of making a special trip to get rid of waste or leave anything that might attract predators. 

What's the Poop?

The researchers think that the ants might maintain toilets inside the nest because the feces has some use to them. One potential benefit to keeping frass in the house is that it might keep fungus out. Some termites produce poop that slows and stops fungal growth and they line their nests with fecal pellets to protect themselves from infection. The ants might be doing the same, or maybe they hang on to their waste because it has the opposite effect and promotes fungal growth. Some ant and termite species grow fungus for food and use feces to fertilize their gardens. A third possibility is that the frass provides nutrients not for fungus, but for the ants themselves. Yes, they might be treating their tiny toilets like pantries. Frass from adult ants may contain salt and micronutrients that went unused and could be fed to ant larvae. Figuring out which, if any, of these explanations is right is a subject that’s ripe for study, Czaczkes says. In the meantime, he’s collecting collecting observations of toilets in other ant species’ nests in the comments on the paper.