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June 07, 2024

Jorō spiders likely are coming to Philly. But it may take them years to arrive, and there's no need to panic

The invasive species gained notoriety following news reports of their northward spread, but scientists say the arachnids don't actually fly, and they're not harmful to humans and pets.

Wildlife Spiders
Jorō Spider Georgia David Coyle/Clemson University

The invasive Jorō spider species could migrate to Pennsylvania and New Jersey in the coming years. But scientists say they're not poisonous to humans and, contrary to some media reports, don't actually fly.

The Jorō spider, an invasive species that arrived in northern Georgia a decade ago, is expected to eventually make its way to the Northeast, where its reputation – perhaps unnecessarily negative – precedes it. 

In January, 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. Earlier this month, an ABC News article fretted that the "creepy crawler" could spread up the East Coast as soon as this summer, and other publications, including NBC New York, reported the same timeline.

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 So, are the Jorō spiders, which are native to Asia, actually coming to rain down on our summer fun in the Northeast?

"Maybe, or maybe it's a decade; you can't predict the future," said 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. "So, nobody knows when they're going to get there. Or if they're going to get there, right, that's the million-dollar question. On their own, they're probably not going to get there in one year, that's just way too far for them to spread naturally."

Since being first found in the United States in 2014, Jorō spiders have spread outward in all directions from northern Georgia  at about 10 miles per year, according to Penn State. At that rate, the species potentially would reach Southeastern Pennsylvania in 35 years, although there are some ways they could arrive much faster. Regardless, scientists do not urge people to be alarmed.

"I don't think it's a panic situation," said Jon Gelhaus, the curator and chair of the Entomology Department at Drexel University's Academy of Natural Sciences. "I don't think there's anything to panic about this. But I certainly don't think it's something people are going to see right away." 

Not only is it unlikely that the Jorō will get here in the coming months, but the spider species also does not actually fly, and its venom is not considered poisonous to humans and their pets.

"People are always scared when they hear about a new invasive species that could do some harm," said José Ramírez-Garofalo, a Rutgers University Ph.D. candidate who studies the way climate affects species' geographical distributions. "But the idea that there are these flying, venomous spiders, which isn't really the case anyway, it seems like it's really gaining traction for better or worse. But I think in this case, for the worse. 

"I think we all need to calm down a little bit. This isn't going to be the next pandemic; it's going to be OK. Even if they do show up in New Jersey and New York and Pennsylvania, they're going to be showing up in low numbers. They're going to be very localized populations. So, there's nothing really to worry about."

Here's what else to know about the Jorō spiders. 

What are Jorō spiders?

Jorō spiders are orb-weaver spiders, meaning they spin spiral, wheel-shaped webs that look like the one in the children's tale "Charlotte's Web," according to Coyle. Adult females are large, with a one-inch body length and a leg span that can reach four 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.

joro spider webDavid Coyle/Clemson University

A Joro spider in its web.

Female spiders lay a single egg sac that can contain between 400 and 500 eggs. The sac is usually attached to bark, leaves or human structures. 

The species is native Japan, North and South Korea, China, Taiwan, Vietnam and India. The Japanese name for the species is "jorō-gumo," which translates to "entangling or binding bride," according to Penn State.

Where are they in the U.S.?

Jorō spiders were accidentally introduced to North America, possibly through shipping containers or potted plant material. They were first found here in 2014 in Georgia. Since then, they have spread throughout adjacent areas of Alabama, North Carolina, South Carolina and Tennessee. There also have been sightings reported in Alabama, Maryland, Oklahoma and West Virginia.

A 2023 study, involving Coyle, determined the species is here to stay in the U.S. and in time likely will inhabit most of the eastern U.S., which has been deemed habitable for the Jorō. 

"This species from Asia is probably more adapted climate-wise to the Northeast, and even further north, than it is to where it was first found, which is in the northern Georgia area," Gelhaus said. "So, it looks like it will be even better adapted here, at least climate-wise."

Despite this, it doesn't mean the species is in any particular rush to get here.

"I think lately, this has been misconstrued," Coyle said. "(Just) because they can survive (in the Northeast), it doesn't mean they're immediately going to get there. Yes, they can live there. No, they're not there yet."

One way the Jorō spreads is through ballooning, a natural dispersal method that can take them tens to hundreds of miles away from their starting points. This method likely is the "flying" that some news reports have referenced, but it is not like the "monkeys in 'The Wizard of Oz,'" Coyle said. Also, don't expect to see fully grown Jorō spiders descending from the sky, because ballooning is reserved for the smallest spiderlings.

"After they hatch, they may be the size of a sesame seed – little, teeny, tiny things," Coyle said. "Some of those will go up on something high, a branch or post and they'll stick their little abdomens in the air and they'll let a bunch of silk strands go and the wind can take some of these. So we call it ballooning. 

"And every orb-weaving species does this, this is not a Jorō thing. Ballooning is a risky endeavor because once you have started ballooning, you've got no control over where you land. So, you might land somewhere awesome. You might land on a windshield, you might land in lake – you don't know what's gonna happen. So, every spider that balloons is not gonna make it, for sure."

Any baby spider that does ride the wind farther north would be tough to spot, and not-so-scary.

"I think the early news reports were making it like these big spiders were gonna balloon into New York City, like some sci-fi movie," Gelhaus said. "If there's any dispersal like that through the wind, it's going to be these little, tiny spiders, which nobody would even pay any attention to. The big ones are not going to be visible until later in the growing season."

The spiders also may travel by unwittingly catching rides with humans. This is one way that the species could show up in the Philly area sooner rather than later.

"They're pretty good hitchhikers," Coyle said. "So they will get on things, picnic tables, swing sets, anything outside that might be transported from point A to point B. And so they could easily be carried up this year. If the right thing was taken from somewhere down here to up in the Northeast, it certainly could happen. But, who knows if it will?"

Are Jorō spiders dangerous?

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 contrast to the villainous portrait sometimes painted lately, Coyle finds Jorō spiders to be rather chill, actually.

"They're super docile," Coyle said. "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."

However, the species potentially could present a danger to the ecosystem. Where Jorō spiders have been found in the U.S., other spiders usually are scarce. This means the Jorō may be displacing native species. Coyle does not believe Jorō spiders are eating other species, but that they're finding the best web-slinging spots first.

"Spiders just go for really good locations, especially orb-weavers," Coyle said. "They want a location that's suspended, where things can fly through. And I think what happens is that Jorō spiders just get there first. Down here in Georgia, they're already out. ... I don't see a lot of other spider species out yet. 

"So, my hunch is that they just get there first. And basically it's first-come, first-serve on those good spots, right? So they're there, they're already starting their web up. And then when the native ones hatch and start crawling around looking for spots, they're kind of relegated to less great spots that are more in the margins or something like that."

Though Joro spiders are considered invasive, don't expect the same stomp-on-sight orders that the spotted lanternfly prompted in recent years. Coyle said there has not yet been any documented economic impact caused by the Jorō spiders. 

"I tend to tell people, if you want to kill Jorō spiders in your yard, and that sparks joy, you do you," Coyle said. "Is it ever going to really impact their population? Probably not, just like killing the lanternflies, honestly, that's not going to impact their population either. That cat's out of the bag, and that ship has sailed."

On the other hand, the possible northern spread of the Jorō is no reason to simply kill any spider on sight.

"Please don't start killing spiders that you see outside because you think they're Jorō spiders," Ramírez-Garofalo said. "It's almost 100% chance it's not. Even if it is, still don't kill it because, chances are, you don't know how to distinguish a Jorō spider from a garden orb-weaver, which is the native species that we have here; there's a couple of them, and they all kind of look the same. Just don't start killing spiders because you think it's a Jorō spider."

What should you do if you see a Jorō spider? 

There's nothing in particular you need to do if you see a Jorō spider. The spider's huge web could pose a "nuisance," as Gelhaus puts it, but the spider and its web can be safely moved with a broom or stick.

Anyone who sees a Jorō could log the sighting in an app like iNaturalist, which allows scientists and others to share their observations from the natural world.

"That's one way we all could kind of track where it's showing up, because people that do see the spider who have iNaturalist will likely upload it, because they'll recognize it as 'Oh, this was an interesting spider.' And once it's full-grown, it's big, the web is big, so people will notice it and probably upload it," Gelhaus said. "And so we'll be able to track it as it moves north." 

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