Other than dung beetles, most animals try their best to avoid poop. Humans typically build entire rooms designed to flush the stuff away. The ick factor evolved for good reason: fecal matter is a great place for microorganisms to live and grow, some of which can lead to serious infection and illness.

Like us, many insects that live in colonies have evolved ways of keeping their nests and hives sanitary. Honeybees perform so-called defecation flights, in which they leave the nest to do their business. Some ants, like leaf-cutters, use their feces as manure for gardens that grow fungal food, but only certain “sanitation workers” are permitted to handle it. Ants in general are well known for their cleanliness—disposing of the dead outside the nest and leaving food scraps and other waste in special refuse chambers.

Thus, University of Regensburg biologist Tomer J. Czaczkes was surprised when he noticed dark patches accumulating in the corners of the white plaster nests in which his black garden ants, Lasius niger, lived. Over seven years of observations, he became convinced the dark patches were made of feces.

To confirm his suspicion, Czaczkes added artificial coloring to the ants' food for 21 colonies. Sure enough, the dark patches started showing up in brilliant shades of red and blue. Because the piles of ant poo never contained food scraps, corpses or other debris, Czaczkes and his colleagues conclude that referring to these spots as “toilets” is apt. The results were detailed in the February issue of PLOS ONE.

No one is sure why black garden ants keep their feces inside the nest, especially given that Formicidae are otherwise fastidious housekeepers. Perhaps it is used for defense, for territory demarcation or as a building material. Or it could serve as a source of salt or other nutrients. Another possibility, according to Czaczkes, is that the waste is stored precisely because it is stinky. “Ants tell friend from foe apart by their smell,” he explains. “Perhaps newly emerged ants go to the toilet and sort of ‘bathe’ in it, to pick up the colony smell quickly.” Each explanation is plausible, so more research will be necessary to determine the best one.

“The next obvious step is a lot of boring observation, where I hope to catch the ants using the toilets,” he says. To covertly watch them do their business, Czaczkes will have to make nests with see-through lids and work under red light, which the ants cannot see. Onward, entomology.