Jorō spiders caused quite the stir a few months ago when experts predicted the giant arachnids that arrived in the United States a decade ago could make its way here within years. While claims that they're venomous, flying monstrosities have largely been debunked, it appears the invasive species has arrived in the Philly region much sooner than expected.
Six Jorō spiders were found in Northampton Township, Bucks County, this month, according to Joro Watch — an interactive monitoring program run by the University of Georgia's Center for Invasive Species and Ecosystem Health. An entomologist traveled to the scene to confirm that they were adult Jorō spiders, marking the first known sighting in the state, but it's not yet known if it's a single occurrence or a newly established population of the species there.
The first U.S. sighting of Jorō spiders, which are native to Asia, was in northern Georgia in 2014. Since then, Jorō spiders have spread in all directions at about 10 miles per year, according to a 2022 Penn State study. At that rate, the species was estimated to naturally reach Southeastern Pennsylvania in 35 years.
But that timeline was called to question in January, when a New Jersey-based pest control company put out a notice claiming the state would have "giant venomous flying spiders" by the end of the year. Then in June, ABC News and NBC New York fretted that the bugs could spread up the East Coast over the summer.
And now, there are at least a few of the spiders in the area, and they may have had a little help traveling up to Bucks County.
"Large geographic jumps that happen like this are most often due to the species being transported by humans, most commonly unintentionally," said Rebekah Wallace, of the Center for Invasive Species and Ecosystem Health.
What are Jorō spiders?
Jorō spiders are orb-weaver spiders, meaning they spin spiral, wheel-shaped webs. Adult females are large, with a 1-inch body length and a leg span that can reach 4 inches. The females are also brightly colored, with bodies that are yellow with grey-blue bands. Their long legs are black with yellow bands. Adult males are much smaller and duller in color.
The webs that adult females spin can be up to 10 feet wide and are suspended between objects like trees, bushes and light posts. Males do not create webs, and instead are found in females' webs. Depending on their size, Jorō spiders eat almost anything that gets caught in their web, including flies, mosquitoes, butterflies, wasps and cockroaches. Their diets can also include another invasive species that's been grabbing headlines in recent years, the spotted lanternfly.
But unlike in the case of the spotted lanternfly, don't expect the same stomp-on-sight orders for Jorō spiders. There has not yet been any documented economic impact caused by the Jorō spiders' presence in the United States, according to David Coyle, an assistant professor at Clemson University who has conducted research into the species and its spread since he found an influx of the bugs in his Georgia yard in 2020.
Coyle was involved in a 2023 study that determined the species is here to stay in the United States and in time likely will live throughout most of the eastern United States, which has been deemed habitable for the Jorō. Along with Georgia and now Pennsylvania, there have also been sightings of the species in Alabama, North Carolina, South Carolina, Tennessee, Alabama, Maryland, Oklahoma and West Virginia.
Should we be scared that the Jorō has arrived in Pa.?
Arachnophobia aside, there's not necessarily a medical reason to fear Jorō spiders. They are "reluctant biters," according to Penn State, and have small fangs that would have difficulty piercing the skin of a person or pet. Jorō spiders do have venom, as nearly all spiders do, but their venom is too weak to produce much more than localized pain and redness that should clear quickly without intervention. They also would not try to enter a person's home. In fact, they're pretty chill as far as giant spiders go.
"They're super docile," Coyle said in June. "I've held them dozens of times, if not more; my kids have held them. They just crawl around and they're just kind of hanging out. They're not aggressive. And I think anyone that gets bit by a Jorō has probably had it coming, whether they're shaking it or something. They're not just out there biting stuff. So yeah, I think it probably takes some work to get bitten."
They also don't fly, as some reports have insinuated that giant spiders will descend upon the region from the sky. Instead, like all orb-weaving species, the Jorō spreads through ballooning, a natural dispersal method that can take them up to hundreds of miles away from their starting points. Ballooning only happens when they are newly hatched spiderlings, about the size of a sesame seed, when they let silk web strands catch the wind.
The theory that the arachnids made it here with human help could be the most likely explanation for their arrival, since the Jorō spiders are "pretty good hitchhikers," Coyle said, and they could latch onto outdoor items like picnic tables or swing sets that are being transported long distances.
While the Jorō so far has not been deemed threatening to people, pets or the economy, the invasive species could present a danger to the ecosystem. Where Jorō spiders have been found in the United States, other spiders usually are scarce. This means the Jorō may be displacing native species, potentially because they're finding the best web-slinging spots first.
If you do happen to see a Jorō spider, you could log the sighting through Joro Watch or the iNaturalist app, which allows scientists and others to share their observations from the natural world.
