Will Pennsylvania see giant, flying Joro spiders? We asked a Penn State scientist
Penn State entomologist Michael Skvarla has watched the news with a growing sense of dread in recent weeks as sensational headlines warned of giant, flying Joro spiders taking over the East Coast this summer.
It’s true, the females can get pretty big, attaining a leg span of 3 or 4 inches, potentially. Joros also kite around on web-spun parachutes – but only as spiderlings, something many spiders do to disburse.
But the one thing Joro spiders aren’t is dangerous (unless you happen to be a bug they enjoy eating).
When Skvarla saw the story was taking off, he quickly penned an explainer for the Penn State Extension Office, hoping this wouldn’t be a repeat of the murder hornet mania he endured a few years ago.
“I wrote that to get ahead of it,” Skvarla said, joking he’s still haunted by tamping down fears about murder hornets two years ago.
We asked Skvarla to help us separate fact from fiction. Ultimately, he says Joro spiders are harmless and aren’t likely to arrive in Pennsylvania any time soon.
Where do Joro spiders come from?
Japan, originally.
Joro spiders take their name from the Jorogumo, a creature out of Japanese legend that can shapeshift between a spider and a beautiful young woman to lure and devour men.
It’s unclear how exactly the Joro spider colonized the U.S.
Skvarla speculates it was likely via shipping containers or potted plants brought here from overseas. Their native range spans across East Asia, including as far south and west as mainland Thailand and India, respectively, and as far north as the Korean Peninsula.
Joro spiders in the U.S. are more common in Georgia and the Southeast, but their adaptability to the cold may mean they can survive much farther north, like in Pennsylvania (more on that in a bit).
Are Joro spiders poisonous?
Technically, they’re venomous.
They’re not poisonous since the method of delivery is via injection by bite.
However, Joro spiders’ fangs are too small to break human skin, and they’re only really a threat to their prey, in this case, pests.
Are Joro spiders harming the environment here in the U.S.?
We don’t know. Their exact ecological impact still isn’t fully understood by entomologists, the scientists who study all manner of bugs.
Skvarla likes to call Joro spiders an “introduced” species, rather than invasive, because the latter label might confer a negative stigma that isn’t deserved.
When Joro spiders took over yards and front porches all over north Georgia last year, they were mostly just a nuisance – leaving residents there sputtering and swatting the air after wandering into webs.
Some have wondered if Joro spiders might negatively impact local pollinator populations or out-compete similar native spiders.
Skvarla doesn’t see them impacting pollinators here, as the Joro population would need to grow to a pretty big size for that threat to be viable.
He speculated they could interbreed with the similar Gold Silk Weaver spider and create a hybrid that could outperform other native spiders, but that remains an open question.
Will we see Joro spiders in Pennsylvania?
Not likely any time soon.
Joro spiders can get around as spiderlings by hitching a ride on air currents with their webs. That said, they don’t get very far unless, for example, they’re picked up and hurled by hurricanes.
“They’ve been moving 10 miles a year on their own” in Georgia, Skvarla said.
Still, because of climate change and the Joro’s acclimation to the cold, it’s possible their range could get much wider in the U.S.
According to a recent Physiological Entomology article that touched on the spider’s suitability to cooler climes, the Joro matures faster and has a much higher metabolism – including a heart rate 77% higher when exposed to low temperatures – than its cousin.
“These findings suggest the joro spider can exist in a colder climatic region than the southeastern USA which can be useful information for management or planning purposes,” the article’s authors wrote.
This story was originally published March 18, 2022 at 11:19 AM.