Pavement ants (Tetramorium) on human food in a Manhattan street median

Pavement ants (Tetramorium) on human food in a Manhattan street median. Pavement ants were the most common species found on street medians. Photo credit: Amy Savage

Ants—they’re everywhere. Charging across your picnic blanket, sneaking into your sandwich and, naturally, marching one by one (hurrah! hurrah!). Throughout the temperate zone you’ll find ants swarming in almost every forest, ducking beneath blades of grass in virtually every prairie.

Forests and prairies are hard to come by in New York City. But in a study published in the November issue of Insect Conservation and Diversity, researchers report that millions of urban ants have settled for what appears to be the next best thing—the grassy median strips that divide Manhattan’s busy streets.

The findings suggest that some swathes of city concrete may foster just as much insect diversity as heavily wooded areas. “We looked at tiny strips of green in the middle of two lanes of traffic with the subway running underneath,” says study co-author Amy Savage, an ecologist at North Carolina State University. Savage found almost 20 different ant species in those median strips, alone.

Collecting Bugs for Science

Ants are one of the go-to organisms for studying species diversity. That’s because they can survive in many different environments, and also because they are surprisingly diverse, with over 12,000 species worldwide. “Ants—which I love to watch—are some of the best systems for understanding environmental variation,” Savage says.

Savage has spent much of her career studying why some environments have a greater diversity of species than others. In urban ecosystems, where humans have considerably altered the environment, that question is particularly pressing. “I’m really interested in diversity within cities,” she says. “Urban planning decisions are affecting what kind of diversity we see on the ground.”

But insect hunting in the big city isn’t always easy. In their study Savage and her team spent days sifting through blades of grass on cramped Manhattan median strips while cabbies and bus drivers sped by. “We don’t infuriate people too much, but we do confuse them,” she says. “We actually had a lot of interesting conversations with taxi drivers waiting at stop lights.”

An Insect Census

Beyond median strips, Savage and her colleagues collected ant samples from about 50 sites in Manhattan, including parks and urban forests. In total, they found 42 ant species in the city, with median strips alone accounting for 18 different species. That’s five more species than a prior study of urban median strips reported in 2010.

Savage says that the previous research inspired her to take the experiment one step further. “We were interested in understanding the context of that [study],” she says. “We wanted to use that as a launching point to compare other habitats in the city.”

One of the most surprising findings, Savage says, was that the proximity between urban habitats had relatively little to do with species diversity. When she compared ant populations in an urban forest with those of a nearby park, she found very few of the species lived in both habitats, despite the shared border.

But when Savage compared urban forests--even ones that were very far apart--she discovered striking similarities. “Habitat type was more important than proximity,” she explains.

Why Urban Ants Matter

The population and diversity of ant species in an ecosystem can be central to its success. “Different species have different affinities, they nest differently, turn over soil differently, eat different types of food,” Savage says. “More diversity will likely mean greater ecosystem services than just one ant species.”

For this reason, scientists have already studied ant population dynamics in national parks and forests. But Savage suspects that ant diversity could also be crucial to holding urban ecosystems together. “Some ant species may keep pest populations down so trees can survive,” she says. “Others might be important for eating a fallen piece of street food.”

Savage hopes that her research will help arm ecologists and policymakers with the information necessary to protect species diversity both in national parks and between city streets. “People don’t realize how important ants are to their daily lives,” she says. “There’s more complexity in these urban habitats than we usually think.”