1st sighting of giant, parachuting Joro spiders reported in Pa. burbs. Big deal?

Arachnophobes, look away — there's a giant invasive spider that has reportedly arrived in the the tri-state area.

Earlier this year, experts warned that Joro spiders could start showing up in Pennsylvania, New Jersey and Delaware this summer, spreading up from the southeastern U.S., where they have been proliferating.

Joro spiders spotted in suburbs of Philadelphia

Now, there is a report of six of the creepy invasive crawlers in southeastern Pennsylvania on JoroWatch.com. (Yes, that's a real website powered by the University of Georgia and other academic and environmental entities.)

Someone spotted the group of a half dozen or so colorful arachnids in the yard of a home in Warminster, Bucks County, on Sept. 5, 2024, JoroWatch said.

What is a Joro spider?

The yellow and black arachnids are native to East Asia, but the invasive arachnids have been around in Georgia for about a decade. A fall of 2023 peer-reviewed study conducted by David Coyle, a scientist and assistant professor in the Department of Forestry and Environmental Conservation at Clemson University, found that the species is "here to stay" in the U.S. as it spreads rapidly around the country.

As of October 2022, the species' range spanned at least 120,000 square kilometers across Georgia, South Carolina, North Carolina and Tennessee, according to the study. There were also reports of Joro spiders in Alabama, Maryland, Oklahoma and West Virginia. And the spiders are expected to make more East Coast states their home in the future.

“(The data from the study shows) that this spider is going to be able to inhabit most of the eastern U.S.,” Coyle said. “It shows that their comfort area in their native range matches up very well with much of North America.

"Barring some unforeseen circumstance, we expect the range of these things to continue expanding, likely to the north, and we’ve already seen that with some populations in Maryland."

Adding to nightmares, the spiders are light enough to travel through the air by a process called "ballooning," making it even easier for them to spread. The "spiders move through the air by releasing gossamer threads to catch the wind and go airborne, at the mercy of air currents and electric fields, although human-mediated transport cannot be discounted," Coyle wrote.

What does a Joro spider look like, how big is it?

Female Joro spiders, a.k.a. Trichonephila clavata, can have a body about 1 inch long and legs that span up to 4 inches, according to a 2022 Penn State Extension article. The females are brightly colored, whereas the males are brown.

But there is good news: Even though its palm of your hand size tends to freak people out, the species is relatively harmless to humans and pets.

Are Joro spiders dangerous?

While Joro spiders may appear frightening to some, they are relatively harmless to people and pets, a University of Georgia study from last year said. In fact, that study found that Joro spiders "may be the shyest spider ever documented."

The spiders will only bite if they're cornered and even then their fangs likely wouldn't be large enough to pierce human skin, according to the University of Georgia study.

"Our paper shows that these spiders are really more afraid of you than the reverse," said Andy Davis, lead author of the study and a research scientist in UGA’s Odum School of Ecology.

Another positive about the spiders: they don't want to go inside homes, according to Coyle. They will instead spin webs on the outside of houses or other structures. If a Joro spider needs to be moved, Coyle suggests using a broom or stick to place it elsewhere.

Might Joro spiders spread further in the Delaware Valley soon?

The simple answer is maybe, but not to worry too much.

"In their native range, Jorō spiders can be found in relatively cold areas – the average January temperature of northern Honshu, Japan is 25–32 °F, similar to most of Pennsylvania," the Penn State article said. "So it is likely that they will be able to spread throughout eastern North America at least as far north as Pennsylvania and possibly further in warmer, coastal areas."

"Between 2014–22, Jorō spiders spread outward in all directions from the location they were initially found by 50–80 miles, or about 10 miles per year. At that rate, they may reach southeastern Pennsylvania in 35 years and northwestern Pennsylvania in 60 years. However, spiderlings are capable of moving tens to hundreds of miles via ballooning," Penn State said. "Additionally, as they increase in numbers, the risk of human-mediated transport to new areas also increases. This means that the immediate risk of Jorō spiders appearing in Pennsylvania is relatively small but will increase year over year as they spread naturally, via high wind events, and through accidental human transport."

University of Delaware’s Department of Entomology and Wildlife Ecology entomologist Dr. Doug Tallamy has been downplaying a potential Joro invasion.

"It's possible but very low on the list of things we should be worried about," he wrote earlier this year. Reached on Wednesday by NBC10, he wrote: "I think it's a non issue that should not be blown out of proportion."

How did Joro spiders get to the U.S. to begin with?

Joro spiders are native to East Asia. It's believed the species likely made its way to the U.S. via a shipping container.

Are Joro spiders orb-weavers?

Joro spiders are in the family of orb-weavers, which spin large, orb-shaped webs. They look similar to garden spiders and banana spiders.

Do Joro spiders fly?

The pattern in which Joro spiders have spread "suggests it is primarily driven by natural dispersal mechanisms, such as ballooning," according to Coyle's study. Ballooning is when spiders move through the air like a parachute by releasing "sail-like trails of silk that lift them up and off into the wind," per National Geographic. (Want to get a bit freaked out? Read the full Nat Geo story.)

The study said human-mediated transport can't be discounted, either, in regard to the spread of the species.

What do Joro spiders eat?

Joro spiders aren't exactly picky eaters. Coyle said they "don't seem to care what gets in their web." The spiders eat mosquitoes, yellowjackets, stink bugs and even spotted lanternflies -- another invasive pest.

"They're just as likely to eat brown marmorated stink bugs as they are to eat a Monarch butterfly," he added. "To say they’re more beneficial than another spider is just simply wrong — they’re a spider — and if something gets caught in their web, it’s going to get eaten. And they don’t care if it’s a rare native pollinator and there are only a few of them left in the world or if it’s a brown marmorated stink bug."

An interesting find from Coyle's study is that Joro spiders are displacing native species, along with having other negative impacts. But it's unclear exactly why other species are being negatively impacted by Joro spiders.

“These are not just benign spiders coming to catch and kill bad things; these are pushing out native species and catching and killing whatever happens to get in their webs,” Coyle said. “Are they bad or good? It’s very nuanced depending on your perspective.”

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