Yes, big spiders are spreading in the U.S. No, they're not flying.

They're not after you. And they don't "parachute" from the sky.

Periodically, people and headlines on the internet have expressed concern about the spread of the invasive Joro spider, a big, striking arachnid that almost certainly hitched a ride to the U.S. aboard a shipping container, as many invasive species do. Since 2013, the palm-sized animals have colonized northern Georgia, and several research teams have found compelling evidence that the species will inevitably expand around the Southeast and along the Eastern Seaboard.

Crucially, these spiders may look imposing, but they aren't a dangerous menace to people. Their potential impact on the environment remains unknown. (They might even have ecological benefits.) And the sizable mature adults definitely aren't going to "fly" or "parachute" down from the sky en mass (as numerous popular headlines or social media posts have claimed), like something out of a low-budget horror film.

Instead, the ways Joros will often expand to new regions in the U.S. are rather mundane.

"It's more likely one of the spiders will hitch a ride on someone's car," Andy Davis, an ecologist at the University of Georgia who researches the Joro spider, told Mashable.

"It's more likely one of the spiders will hitch a ride on someone's car."

The spider will colonize more areas. "It's definitely expanding its range," explained Davis. He suspects the Joros will occupy pockets of the Eastern Seaboard in the coming years, and that they'll occupy most of the Southeast in five to 10 years.

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Beyond cars, the Joros will likely hitch rides on cargo incessantly moving around the U.S. "It got here hiding in cargo," said Robert Furey, a spider expert at the Harrisburg University of Science and Technology.

"Cargo moves," Furey, who had no role in recent Joro research, added. "There's nothing to stop it."

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Why the spiders won't "parachute" down

The claim that Joro spiders will parachute down from the sky is "super ridiculous," explained David Coyle, an assistant professor of forest health and invasive species at Clemson University.

Here's what's actually happening: Some little spiders, like a young Joro spider, may choose to "balloon." This means they release a strand of silk from their abdomen and are able to ride through the air. It's a common way for some spiders to disperse.

But it's not something all spiders do. And it's not something big spiders can do, because they're too heavy. "It's why you don't see a battalion of spiders flying at you," said Coyle. So, no, three-inch spiders won't be "parachuting" across the Eastern U.S. and landing on you.

A mature female Joro spider can be the size of a small plate. Credit: Benjamin Frick

What's more, ballooning is simply a risky choice for an animal. That's likely why some spiders don't balloon. "You can end up in a lake — or on the hood of a truck," noted Coyle. "Your fate is not in your control anymore."

As the Joros expand their reach in the U.S., you shouldn't expect to see any tiny baby spiders ballooning through the woods. When little spiders ride puffs of wind, it's extremely difficult to see. "It happens all the time," said Furey. "When's the last time you noticed it?"

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Furey has never seen a ballooning spider land. "And I spend a lot of time with spiders," he said.

Are Joro spiders venomous or threatening?

No. Joro spiders have much better things to do than seek out, or try to harm, humans.

"With very few exceptions, insects and arthropods want nothing to do with you," said Coyle, noting the spiders' need to build webs, eat, and mate. "They're just doing their thing. People just need to chill out. This thing isn't there to get you."

They are not venomous like a black widow or brown recluse. Their fangs are tiny, so it's not easy for them to bite a person (maybe if you pick one up you'll get an insignificant pinch, noted Davis). And if you disturb them, they're likely to scurry away. In fact, research has found that these spiders are shy or docile.

"It turns out these spiders are real wimps," said Davis.

"People just need to chill out. This thing isn't there to get you."

But as the Joros spread in the U.S., more people will see their big, conspicuous webs in the summer, when they mature. "Their webs are huge," Davis marveled. "They're all over my backyard." And they'll almost certainly become a nuisance. Some people will inevitably run into these big webs, perhaps out on a walk or hike. That will be unpleasant, or startling, because their silk is exceptionally strong.

"It's stopped me in my tracks," said Furey.

A cluster of big spiderwebs from the Joro spider. Credit: Benjamin Frick

Where will the Joros spread?

A close relative of the Joro, the golden silk spider, can't tolerate the cold. That's why it hasn't spread beyond the Southeast.

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But how will the Joro fair? To test their vulnerability to cooler climes, researchers exposed Joros to brief freezes in the laboratory, the type that often kill golden silk spiders. The Joros survived deep freezes considerably better (74 percent survived, versus 50 percent of golden silk spiders). Their faster metabolisms and bodies worked well in colder environments, too. What's more, in their native Japan, the Joros inhabit cooler, northern climes, similar to those on the Eastern Seaboard.

"They're going to expand."

"The Joro seems more cold tolerant," said Davis, an author of the research. "It will probably be able to exist much farther than the Southeast."

How far, exactly, is uncertain. People have already spotted them in the likes of Tennessee, North Carolina, and South Carolina.

"They're going to expand," said Furey.

What risks do invasive Joros pose to the environment?

It's still unknown whether Joros will have a positive, neutral, or negative impact on the environment. Some invasive species wreak havoc on native habitats or agriculture. Take, for example, the colorful spotted lanternfly, which relentlessly destroys trees and crops in parts of the U.S. ("Squash it, smash it ... just get rid of it," urges the state of Pennsylvania.)

But in the early stages of the Joro expansion, ecologists and biologists simply don't have adequate proof of how the arachnids might affect the natural world. "It's guessing at this point," said Davis.

Their multiplying numbers could potentially be a boon to the environment. Hanging out in the open, Joros could become prey to the likes of lizards, birds, and wasps, Davis said. Already, there's some evidence Joros devour another problematic invasive species, the brown marmorated stink bug.

Americans will see more Joros. They won't endanger us. But will they become an environmental curse, blessing, or just (at times) a nuisance?

"Only time will tell," said Furey.

This story has been updated.