Ants are ubiquitous in nearly every urban setting, but why? They thrive despite not having traditional living spaces, nor many of their natural food sources. According to an isotopic study by NC State researchers to determine the diet of urban ant species, it’s because some of them have adapted to enjoy the same kind of junk food that sustains millions of city-dwelling humans.
“We wanted to learn more about why some ant species are able to live alongside us, on sidewalks or in buildings, while other species stay on the outskirts of human development,” says Dr. Clint Penick, lead author of a paper on the work and a postdoctoral researcher at NC State. “This could also help us determine which species are doing the most to clean up our trash.”
Working in Manhattan, Dr. Penick and his team collected 100 ant specimens from 21 species and analyzed their bodies for carbon isotopes. Also used in carbon dating, carbon isotopes also reflect our diets, as our bodies absorb carbon from food. Carbon-13 is of particular interest because it’s associated with grass plants, including corn and sugar cane. That makes it a good marker of human foods, as practically everything we eat is touched by corn and sugar – think of sweets, and even foods not associated with corn, like beef that was finished on corn before slaughter.
As it turns out, ants who eat more like humans have higher levels of carbon-13. The closer to humans they live, the more their diet mirrors our own – ants found in medians had higher levels of carbon-13 than those found in parks, for example. The pavement ant, found in medians and sidewalks, had the highest levels. Only one species, Lasius cf. emarginatus, a relative newcomer to NYC, was found in medians and sidewalks but did not show a preference for human food.
“Human foods clearly make up a significant portion of the diet in urban species,” Penick says. “These are the ants eating our garbage, and this may explain why pavement ants are able to achieve such large populations in cities.”
Of course, it’s not yet known whether ants actually have a preference for human junk food, or just find it convenient in terms of availability and caloric density. More research is needed to determine whether the ants are merely opportunistic, or have fully adapted to urban life. [NC State]