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Broadway, New York.

People bustle around the intersection of Broadway and 43rd Street in New York City (file photo).

Photograph by Mark Lennihan, AP

An ant.

An ant walks across its colony hive in Italy. Photograph by Daniele La Monaca, Reuters

Christine Dell'Amore

National Geographic News

Published October 13, 2010

An unexpected cast of characters has found a home on Broadway: At least 13 species of ants mingle along the famous thoroughfare and other Manhattan streets, a new study says.

This insect diversity surprised scientists, who discovered the many ants living on street medians in New York City, the United States' largest metropolis.

Just like human New Yorkers, the ants are a jumble of personalities, from the tiny thief ant—which, as the name suggests, feeds its colonies with stolen food—to the street-smart pavement ant, a fiercely territorial insect that nests under cement. (See ant pictures in National Geographic magazine.)

Though most of the species are native to North America, the team also found a few foreign species living peacefully among the locals, likely having hitched a ride to the Big Apple in soil from potted plants or wood mulch.

For instance, the poisonous Asian needle ant had never before been found north of Virginia. (Also see "Brain-Controlling Flies to Triumph Over Alien Ants?")

Not all alien species are detrimental to native species. "Quite the opposite," study leader Marko Pećarević, a Columbia University ecologist, said in an email. "Given enough time—centuries or millennia—they tend to complement the native richness.

"The problem is that one in a hundred will be an invasive, and cause great damage to the environment, usually by altering habitats and/or directly killing other species," he added.

Despite this rich diversity, for ants Manhattan is more a mixing bowl than a melting pot, the study authors noted.

"While we humans all belong to the same species and hence can reproduce and 'melt' our ancestral differences into a beautiful amalgam that is New York, the ants that make up the diversity found on the medians in NYC are truly different species and cannot reproduce, but merely mix and coexist,"  Pećarević said.

(Related: "Ants Practice Nepotism, Study Finds.")

Ants Adapting to City Life

In the summer of 2006, Pećarević and colleagues trapped ants on 44 medians along Broadway, Park Avenue, and the West Side Highway on Manhattan Island. (See pictures of what Manhattan may have looked like in 1609.)

All the medians supported some type of vegetation, from the well-manicured lawns of Park Avenue to the tree-lined patches on Broadway, he said by email.

Since past studies of urban wildlife have focused mostly on areas that more closely mimic nature, such as gardens, observing medians or other built elements could reveal unknown animal habitats, the study said.

Predictably, the larger medians host more species, he said. Some species, such as the pavement ant, prefer medians with more concrete.

Others, such as the Asian Nylanderia flavipes, like areas with more trees, according to the study, which appeared October 5 in the journal PLoS One.

Still other ants live underground, including the cornfield ant, which "herds" aphids like people care for cattle.

Future studies that collect ants from trees may reveal additional species in New York City, for a total of about 30, Pećarević predicted.

Eric Lonsdorf, director of the Urban Wildlife Institute at Chicago's Lincoln Park Zoo, said he was surprised by how many species were discovered in such small strips of land.

Lonsdorf was also intrigued by the idea of ants adapting to life in the city. For instance, past research has shown that odorous house ants living in cities set up larger colonies with multiple queens, according to the study.

Seeing "urban as a particular kind of habitat for animals, rather than universally unsuitable, is a shift in thinking," Lonsdorf added.

City Critters Poorly Understood

The new research is a reminder that the pockets of nature urbanites encounter each day remain poorly understood—even as more people move into New York and other cities, the study says.

Indeed, finding such an assortment of ants in a city of eight million humans is "more evidence that we know little about how animals perceive urban areas as habitat," Lonsdorf said.

According to study leader Pećarević, urban wildlife does a "lot of work that makes life more pleasant for us, such as waste removal, seed dispersal, [and] pollination of flowers, to mention but a few."

So the next time you're downtown, "take a few minutes to sit on a bench and look at ants go about their business," he suggested.

"There is a whole new world to discover out there."

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