In yet another example of ants displaying a "uniquely human" trait, researchers found that black garden ants sequester waste in designated regions within their colonies. (Other former "uniquely human" traits of ants include farming, going to war, and using tools). Many other social insects carefully remove waste from their colonies; why don't these ants do so?
The study authors hypothesize that these homebody ants don't want to leave to nest (which might lead them into danger); thus, it is safer to deposit waste within the colony. To prevent the spread of disease, the ants evolved a system akin to toilets or trash dumps.
Having internal waste sites may also provide further advantages compared to depositing waste elsewhere. Perhaps ants experience "bonding time" near the loo, like naked mole rats (which regularly visit toilet areas and coat themselves in waste as a badge of group membership). It is also possible that the waste reservoirs have some nutrients that are useful to ant larvae.
"Ants are indeed tidy creatures, but we must be careful not to anthropomorphize," says the study leader Tomer Czaczkes, adding "they are not tidy because it brings them satisfaction, but rather because there must be a selective advantage to being so." However, often traits that confer a selective advantage manifest themselves through an internal reward system, such as a feeling of satisfaction. For example, why do many humans crave love and long-term partnership? Because the trait of "having a long term partnership" confers an advantage (biparental care of offspring; better resource acquisition; etc). We derive satisfaction from love and partnership because satisfaction is the evolved mechanism to reward us for manifesting a selectively valuable trait!
Thus, even though sequestering waste likely confers a selective advantage to ants, it is very possible that in each individual, the reinforcement mechanism is a feeling akin to satisfaction.
For those fascinated by examples of ant culture and cognition, I recommend the science fiction short story Microcosmic God, by Theodore Sturgeon.
The first in-depth look at ant bathroom habits has found that some of the insects maintain "toilets" in their intricate underground colonies. Scientists studying black garden ants discovered that the bugs pile their waste in dedicated corners of their nests. This makes sense: With thousands of ants confined to such a small space, organization is key.