College of Arts and Sciences Newsroom

Can a patch of greenery on top of a downtown building really count as wildlife habitat, even for bugs that have to scale 90 feet of concrete to get there?

For ants, the answer is yes, according to a new study in Urban Ecosystems by Grace Walusis and associate professor Chelse Prather. As an undergraduate, Walusis led the field work, analysis and writing, funded by a Keck Environmental Fellowship.

The team sampled ants on nine green roofs and the plants growing at street level nearby in Dayton, Columbus and Cincinnati. They found fewer ants up top, but largely the same kinds of ants doing the same things. On both roofs and ground, the ants overwhelmingly went for sugar over salt.

The bigger surprise was what that overlap suggests. The roofs almost never had ant nests, the size and height of the building didn't matter, and the researchers kept spotting worker ants climbing straight up the sides of buildings. The likely explanation: the rooftop ants and the ground ants are often the same colonies, with workers nesting at street level and commuting several stories up to forage for sugar from flowers, aphids and even people's leftover food.

"It's surprising, because scaling a multistory building is a huge effort for an ant," Prather said. "What it tells us is that green roofs aren't isolated islands. They can be part of a connected web of habitat running right up the sides of our buildings. Even small green spaces in a city can give insects more room to live and feed."