Stinging Asian needle ants march into Philly

Largely undetected, the Asian needle ant steadily invaded North America over decades, wielding a painful sting that can trigger life-threatening anaphylaxis in some people.

Now, the insect — native to China, Japan, and the Korean Peninsula — has spread into Philadelphia, according to confirmed sightings on the popular nature reporting app iNaturalist.

To date, there have been only three sightings of Brachyponera chinensis in Pennsylvania, and all are in Philadelphia, according to the app. None has been reported in New Jersey.

The first local sighting was noted in May 2020 on Krams Avenue in Manayunk. The second was recorded in July 2023 on Delaware Avenue in Philadelphia. And the latest was in April on Woodland Avenue in Elmwood Park.

Experts say that the ants are not yet a major threat to homeowners and picnickers, but that they are decidedly unwelcome because of their sting and the environmental damage they can cause.

“The big takeaway for the public right now is that the Asian needle ants do seem to be here, but we’ve really no idea how far, wide, and spread they are, so it’s kind of a black box at the moment,” said Michael Skvarla, assistant research professor of arthropod identification at Pennsylvania State University’s Department of Entomology. “There’s no reason for undue panic, but we do need to figure out where they are and how abundant they are.”

According to the U.S. Department of Agriculture, Asian needle ants are “small, shiny, dark brown to black, with the end of the antennas and the legs being a lighter orange-brown. Worker ants are about 0.2 inches in length.”

Unfortunately for nonscientists, they can resemble other ant species, making them hard to spot. The USDA says that Asian needle ants are not very aggressive — unlike red fire ants, which also sting.

But the stings of Asian needle ants are quite painful, can affect people in different ways, and “can result in life-threatening anaphylaxis, an acute allergic response,” the USDA cautions.

The intense pain of a sting can last several hours, leave skin red, and result in hives. In the most extreme cases, people with a hypersensitivity could experience anaphylaxis, a rapid onset of symptoms including skin rash, nausea, vomiting, and difficulty breathing.

There are not a lot of data to show how many stings result in anaphylaxis. While cases of anaphylaxis have been reported in the U.S., the percentage of people who have the hypersensitivity is unknown. But people who are hypersensitive to other stinging insects may be at increased risk.

Skvarla noted that the ants can cause serious environmental impacts by displacing native ant species that serve as critical seed dispersers. Native ants carry seeds and ensure the spread of various plants. Researchers have found big decreases in seed dispersal in forests where Asian needle ants have spread.

In addition, Skvarla said the ants can affect bee populations. That’s because the ants can alter bee habitat.

He said little funding is available to study Asian needle ants. So he plans to drive to the Philly area on his own in the coming months.

“Nobody’s really looked into it,” Skvarla said, “and I’m a little bit worried. I’m going to give it a shot, see if I can’t find them. It also would be nice to confirm that they’re here through gathering physical specimens instead of just photo reports on iNaturalist.”

Skvarla said the ants can be killed with insecticides, but widespread application is not a viable option for forests because of the cost involved and the potential to affect beneficial native animals and insects.

Additionally, there are no known bio-controls — which are natural enemies like predators, parasites, and pathogens — that could be used to control the pest. Skvarla said the ant has not been a major target of the USDA, in part because it has not posed a threat to crops.

Jim Fredericks, a board-certified entomologist with the National Pest Management Association, a trade group, said the ant has been around for nearly a century, but its spread was largely untracked.

The Asian needle ant was first discovered in the U.S. in 1932 and found in at least three southeastern states. It is capable of spreading through temperate forests, such as those in Pennsylvania and New Jersey, by nesting under or in logs, under stones, and within fallen leaves. They can nest near mulch, pavers, and wood landscaping near homes.

Found in Georgia, North Carolina, and other states, the ant prefers to make its home outdoors but can find its way indoors, Fredericks said.

The Asian needle ants’ wider distribution has only recently been recognized because it poses a challenge for homeowners to identify and manage, Fredericks said. He advises calling a professional if you suspect an infestation. Incorrect treatment, he said, could exacerbate the problem.

“There are reports of them both outside and inside homes,” Fredericks said.