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Beneath the feet of millions of New Yorkers, a species of ant—natively found nowhere else in North America—has been thriving in the concrete jungle for more than a decade, surprising scientists with its unique ability to thrive in Manhattan and the rest of the borough. But where the insect came from and why it has adapted so well to this urban environment have remained a mystery.
Now, scientists have discovered the ant’s identity and origins, and it’s a few thousand miles from home. The globe-trotting insect is a native European species known as Lasius emarginatus, which new research shows is common in more natural environments in Central Europe.
Researchers first spotted the insect, dubbed the “ManhattAnt,” while surveying ants in New York City in 2011. To their surprise, the ant — which has a black head and abdomen and a red thorax — didn’t match any of the nearly 800 species found in North America, and the researchers speculated it might be a European species; no further research was done at the time to confirm the species.
But now the insect has grown to the point where it’s the second most common ant in the region, drawing the attention of scientists and New Yorkers who live with the pest, said Clint Penick, an assistant professor of entomology and plant pathology at Auburn University in Alabama.
Entomologists are keeping a close eye on the non-native species to monitor their environmental impact. Still, they have a few theories about how the ant got to North America and why it’s so successful in the big city, according to a study published May 28 in the journal Biological Invasions.
The beginning of an invasion
A 2009 ant survey failed to find any sightings of the Manhattan Ant, suggesting it arrived in the city shortly thereafter. Although it has only called the Big Apple its North American home for a little over a decade, the species has been busy spreading at a rate of about 2 kilometers (1.2 mi) per year.
So far, the insect has also been spotted on Long Island and in several New Jersey cities, the study said. Based on the European climates in which the insect can thrive, the authors suspect that the ant could travel as far north as Maine and as far south as Georgia in the future.
“It’s pretty much taken over Manhattan in a decade,” said Penick, the study’s lead author. “It’s the second most common ant (Tetramorium immigrans), which has been around (in New York) for at least a century.”
So far, the invasive ants have spread naturally via mating flights — when winged ants fly away from the nest in the summer to form new colonies — but the authors predict that the species could spread further via vehicular transport, such as ships and cars, since the species has become so dominant in a large city like New York, Penick said.
This is likely how the ants arrived in North America, according to Corrie Moreau, a professor of biology and entomology at Cornell University who was not involved in the new research.
“Many non-native species or invasive species are transported inadvertently by humans, usually in things like the soil of potted plants or sometimes in ship cargo,” but it’s less common for such insects to establish themselves in their new environment and persist there, said Moreau, who pointed to a 2005 study that found only 12 percent of previously introduced ant species ultimately established themselves in their new environment.
Ants in the Big Apple
To identify the species of the Manhattan Ant, the international team of researchers working on the May study first extracted DNA from the ants and compared it to that of other species, using a global database.
The genetic test confirmed that the ant belonged to the genus Lasius, but to identify exactly which species, the researchers sent specimens to co-author Bernhard Seifert, a leading ant researcher in Germany who has studied native European species. By comparing the New York ants to the European ones, Seifert was able to confirm the ant’s identity.
Because the non-native ants have become so common in New York City so quickly, the researchers first suspected that the Manhattan Ant shared a trait often seen in other successful invasive ant species: a tendency to form so-called supercolonies. Supercolonies are exceptionally large ant colonies consisting of nests that have been known to span hundreds of miles in some cases, Penick said.
“(Ants in supercolonies) really have very little aggression, and they kind of cover the ground and are peaceful within their colony,” he said. Because the colonies work together instead of against each other, they can spread more quickly and easily dominate an area, crowding out native species, he added.
But when the authors tested this hypothesis on the Manhattan Ants by collecting specimens from different nests around the city and placing them together, they found that the ants were aggressive and fought with each other, a sign that these insects maintain the territories that are typical of regular colonies, not supercolonies.
With that theory disproven, the researchers looked for other ways in which the ManhattAnts differed from other common ants in the area. They discovered that the ManhattAnts, one of the few species regularly found on New York City sidewalks, uniquely tap into a specific food source in trees planted along city streets: a sticky liquid known as honeydew, which is secreted by aphids and tree bugs such as the spotted lanternfly.
“Their ability to make that shift and take advantage of these urban structures and habitats (with food sources) that other ants can’t get to is one of the reasons they’re so successful in the city,” said Samantha Kennett, lead author of the study and a doctoral student in the department of forestry and environmental conservation at Clemson University in South Carolina.
In some cases, the ants have also been observed eating human food, while their European counterparts mainly feed on other insects and their feces, Kennett said.
Typically, it’s the non-native insects that end up flourishing that are generalists, Moreau said, meaning they’re not restricted to a specific diet or to certain environments. “Because (the ManhattAnts) are more generalist, there’s a greater chance that they can actually land in a new place and be successful,” she said.
Impact on the ecosystem
The ManhattAnts aren’t harmful to humans, but like any insect, they can be a nuisance if they get into apartments, Kennett said. The ants have been seen as high as the sixth floor of apartment buildings, the study found.
A bigger concern, however, is the potential negative impact the ants could have on their habitats, such as the trees they settle in or the native species they might compete with, she added.
“One of the things we know about many invasive ant species is that they displace native species. The native species that they displace tend to have very specialized roles in the ecosystem. So you’re disrupting that ecosystem when you introduce these species,” Moreau said.
“Maybe we would be less upset if (ManhattAnts) became the birds’ favorite food. But we haven’t seen any ways in which they’re useful, so we don’t know,” she added.
The authors of the May study said they hope further research will identify other traits the ants may have evolved to be successful in their new home, as well as the extent of their current distribution. Through an iNaturalist project, members of the public can contribute observations of the insect by recording sightings of the ants and taking photos to upload to the site.
Time will tell whether the ant has become more than just a pest and whether it disrupts the ecosystem, Penick said.
“Dealing with ants in your kitchen is not the worst thing,” he said. “I think this is the worst thing we see. That’s really my hope.”
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