The findings stem from a study that tested isotope levels in New York City ants to determine the makeup of their diet.
"This could also help us determine which species are doing the most to clean up our trash," said Penick. The researchers collected more than 100 ant samples, representing 21 species, at dozens of sites on sidewalks, street medians and parks in Manhattan.
The ant samples were then analysed to determine the isotope content of their bodies. Animals, including humans, incorporate the carbon in their food into their bodies.
One type of carbon, called carbon-13, is associated with grasses, such as corn and sugar cane. Because corn and refined sugar are present in everything from hamburgers (corn-fed beef) to processed foods, ants that eat a lot of human food have higher levels of carbon-13 than ants that avoid human food.
The researchers found that the most common ant species on sidewalks and medians, the pavement ant (Tetramorium Sp E), had the highest levels of carbon-13.
And, in general, the species found in medians had higher carbon-13 levels than those species found in parks. The ants living in closest contact with humans, Penick said, look more like us in terms of their isotope content.
Also read: Fast food industry on fast track
"Human foods clearly make up a significant portion of the diet in urban species," he said. "These are the ants eating our garbage, and this may explain why pavement ants are able to achieve such large populations in cities," said Penick.
An ant species called Lasius cf emarginatus - only found in NYC within the past five years - is thriving on Manhattan's medians, and is one of the few species other than the pavement ants to be found in high numbers on the city's sidewalks.
But Penick's isotope analysis found that L emarginatus has no preference for human food. The research was published in the journal Proceedings of the Royal Society B.