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Under the feet of millions of New Yorkers, a species of ant — originally not found anywhere else in North America — has been thriving in the concrete jungle for more than a decade, surprising scientists with its unique aptitude to flourish in Manhattan and the city’s other boroughs. But where the insect came from and why it has acclimated so well to this urban setting remained a mystery.
Now, scientists have discovered the ant’s identity and its origins, and it is a few thousand miles away from home. The globe-trotting insect is a native European species known as Lasius emarginatus, commonly observed in more natural settings in central Europe, according to new research.
Researchers first spotted the insect, dubbed the “ManhattAnt,” while doing a survey on ants in New York City in 2011. To their surprise, the ant — with its black head and abdomen and a red thorax — did not match any of the nearly 800 species found in North America and the researchers speculated that it might be a European species; no further research was done to confirm the species at the time.
But now, the insect has grown in numbers so that it is the second most common ant in the area, catching 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.
While entomologists keep a close eye on the non-native species to monitor its impact on the environment, they have a few theories to explain how the ant made it to North America and why it is so successful in the big city, according to a study published May 28 in the journal Biological Invasions.
The start of an invasion
A 2009 ant survey did not catch sighting of the ManhattAnt, which suggests it had arrived in the city soon afterward. Though it has called the Big Apple its North American home for only a little over 10 years, the species has been busy, spreading at a rate of about 2 kilometers (1.2 miles) a year.
So far, the insect has also been observed on Long Island and in several New Jersey cities, according to the study. Based on the European climates that the insect can thrive in, the authors suspect the ant may be able to head as far north as Maine and as far south as Georgia in the future.
“The species has more or less taken over Manhattan in a decade,” said Penick, senior author of the study. “It is second most common to the pavement ant (Tetramorium immigrans), which has been (in New York) for at least a century.”
The invasive ants have so far been spreading naturally through mating flights — when winged ants fly away from the nest to form new colonies in the summertime — but the authors predict that the species will be able to extend farther through vehicle transportation, such as ships and cars, since it has become so dominant in a big city like New York, Penick said.
Such transport is likely how the ants arrived in North America in the first place, said Corrie Moreau, a professor of biology and entomology at Cornell University, who was not involved with the new study.
“A lot of non-native species or invasive species get inadvertently transported by humans, usually in things like either the soil of potted plants or sometimes in ship cargo,” but it is less common for such insects to take hold and persist in their new environment, said Moreau, who pointed to a 2005 study that found only 12% of previously introduced ant species ended up becoming established in their new settings.
Ants in the Big Apple
To identify the species of the ManhattAnt, the international team of researchers who worked on the May study first extracted DNA from the ants to compare with that of other species using a global database.
The genetic testing confirmed the ant was from the Lasius genus, but to identify which species exactly, the researchers sent specimens to coauthor Bernhard Seifert, a leading ant researcher in Germany who has studied the native European species. By comparing the New York ants with 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 ManhattAnt shared a trait commonly seen in other successful invasive ant species: a tendency to form what is known as supercolonies. Supercolonies are exceptionally large ant colonies made up of nests that have been known to span for hundreds of miles in some cases, Penick said.
“(Ants in supercolonies) have really low aggression, and they just kind of blanket the earth and are peaceful within their colony,” he said. Because the nests work together instead of against one another, they can spread faster and easily dominate an area by outcompeting native species, he added.
But when the authors tested that hypothesis on the ManhattAnts by collecting specimens from different nests throughout the city and placing them together, they found that the ants showed aggression and fought with one another, a sign that these insects maintain typical territories seen with regular colonies and not supercolonies.
With that theory ruled out, the researchers searched for other ways in which the ManhattAnts differed from other common ants in the area. They discovered that the ManhattAnts, one of the only species found regularly on New York sidewalks, have been uniquely tapping into a specific food source within trees planted along the city’s streets — a sticky liquid substance known as honeydew that is secreted by aphids and tree bugs such as the spotted lantern fly.
“Their ability to make that shift and utilize these urban structures and habitats (with food sources) that other ants can’t get to is a lot of what is helping them to be 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.
The ants have also been observed eating human food in some instances, whereas their European counterparts primarily feed on other insects and their droppings, Kennett said.
Usually, non-native insects that end up thriving are the ones that are generalists, Moreau said, meaning they’re not confined to a specific diet or to certain environments. “Because (the ManhattAnts) are more generalist, there’s a bigger chance that they can actually land in a new place and succeed,” she said.
Impact on the ecosystem
The ManhattAnts aren’t harmful to humans, but like any insect they can be a nuisance when they end up in apartments, Kennett said. The ants have been observed all the way up to the sixth floor of apartment buildings, according to the study.
However, the bigger concern lies in the potential negative impact the ants could have on their environments, such as the trees they are taking residence in, or the native species with which they could be competing, she added.
“One of the things we know about a lot of invasive ant species is they displace the native species, and the native species that they’re displacing usually have very specialized roles in the ecosystem, so you’re sort of disrupting that ecosystem when these species get introduced,” Moreau said.
“Maybe if (ManhattAnts) became the favorite food of birds, we would be less upset about it. But we haven’t seen any ways in which they’re beneficial yet, so we don’t know,” she added.
The authors of the May study said they hope further research will identify other traits the ants might have developed to become so successful in their new home as well as the extent of their current spread. Through an iNaturalist project, citizens can contribute observations of the insect by noting any sightings of the ants and taking photos to upload to the site.
Time will tell whether the ant has become more than just a nuisance and is disrupting the ecosystem, Penick said.
“Dealing with some ants in your kitchen isn’t the worst thing in the world,” he said. “My guess is that might be the worst that we see. That’s really my hope.”
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