A European ant species has become firmly established in the hyper urban landscape of New York City. How did this happen and what’s the reason for its successful (and rapid) takeover?
An invasive ant has been quietly thriving under the throng of New York City, between the pavers underfoot and in open green spaces. Dubbed the ‘ManhattAnt’, the invasive ant has become a common sighting in the city, with its presence extending to the city’s outer boroughs. But what species is it and why is it thriving in such a distinctly unnatural urban environment?
Since its first sighting in 2011, scientists have been attempting to accurately identify the ant and to understand how it has become so quickly widespread. “The species has more or less taken over Manhattan in a decade,” said Clint Penick, an assistant professor of entomology and plant pathology at Auburn University in Alabama, and 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.”
With a black head, black abdomen and red thorax, its identity has stumped ant experts for several years. Now, in a paper published in the journal Biological Invasions, researchers have confirmed with 93-99% certainty that the ant is in fact the European species Lasius emarginatus. It is the first documented population of L. emarginatus outside of its native range.
Now that it has been identified, scientists are keen to learn more about this invasive intruder, how it has managed to become so dominant, so quickly, and its potential impact as it continues to expand its range at a rate of about two kilometres each year. So what do we know about it?
Within its native range, these ants are primarily found in closed canopy forests, as well as urban and suburban habitats. However, in none of these areas is L. emarginatus the dominant ant species. Although in Germany, in particular, L. emarginatus is commonly found inside people’s homes. It is perhaps no surprise then, that the ant was first discovered in New York’s parks and green spaces, later becoming a problem inside apartment buildings and offices. In 2022, the problem became so bad that local hardware stores in New York City reported selling out of ant baits when residents found L. emarginatus colonies infesting their apartments. How did this ant suddenly become the dominant species in Manhattan?
Typically, invasive ant species have a polgynous (multiqueen), polydomous (multi-nest) colony structure and can spread by budding. This allows them to spread quickly and outcompete local ant species, creating super-colonies. Red imported fire ant, Argentine ant and coastal brown (big-headed) ant are the most well-known examples. However, the scientists behind the study found no evidence that L. emarginatus exhibits supercoloniality. In fact, ants from neighbouring colonies are very aggressive to each other. Despite this, it is expanding its range at an impressive rate through mating flights. Taking into account the current distribution of L. emarginatus in Europe, the study authors believe it is likely that these ants will end up residing across a good portion of the eastern US, with their range extended further through accidental transport in cars, boats and freight vehicles.
So, if not due to its reproductive behaviour, how is the ant taking over Manhattan? One reason for its success in the big city is down to biology. The study noted, “Foragers of L. emarginatus have the fastest walking speed and the best visual system of any Lasius species… which may facilitate their success in urban habitats with smooth stone or concrete surfaces. Based on studies within their native range, L. emarginatus tends to perform best in relatively open habitats with smooth surfaces with low spatial resistance, such as a mixture of concrete and stony surfaces that are common in cities.” With this adaptability to the urban environment coupled with a broad diet supplemented by honeydew produced by the aphids and scale insects found in city gardens, it’s easy to see why it is such a successful invader.
“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,” commented Corrie Moreau, a professor of biology and entomology at Cornell University, New York, who was not involved with the study. “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 specialised roles in the ecosystem, so you’re sort of disrupting that ecosystem when these species get introduced.”
So should the so-called ‘ManhattAnt’ be a cause for concern? The authors of the study say it’s a case of watching and waiting. It does, however, highlight the challenge of predicting the impact of non-native species. L. emarginatus is not (or rather was not) considered an invasive ant of concern. And yet, its human-mediated arrival in the US could potentially have a big impact on the environment.
As pest managers, it shows the importance of being familiar the species native to our area of operation so that any strange arrival can be identified for further investigation.
Further reading: Kennett, S.M., Seifert, B., Dunn, R.R. et al. The ManhattAnt: identification, distribution, and colony structure of a new pest in New York City, Lasius emarginatus. Biol Invasions 26, 2759–2772 (2024). https://doi.org/10.1007/s10530-024-03344-z
‘Scientists identified the ‘ManhattAnt’ — and they have theories on why it’s taking over NYC’ by Taylor Nicioli, CNN. August 23, 2024.
Main image: ‘ManhattAnt’ Lasius emarginatus (photo credit: king maf/iNaturalist)
