Giant Spiders Are Taking Over America's Most Popular National Park—and the NPS Wants Hikers' Help Tracking Them

Joro spiders’ large size and enormous webs have spurred public concern since the invasive species arrived in the United States in 2013. While they’re harmless to people, they may pose a threat to their new ecosystem.

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A female joro spider on the ground (Photo: LITTLE DINOSAUR / Moment via Getty)

The National Park Service is asking hikers to help researchers from the University of Tennessee track a new species of large, invasive spider that’s spreading through Great Smoky Mountains National Park.

Native to east Asia, joro spiders—or Trichonephila clavata—are a particularly conspicuous species of web-building spider. While the males are tiny, the black-and-yellow-striped females are among the largest spiders in the U.S., reaching leg spans of up to 4 inches. The spiders rarely bite and are completely harmless to people, but their habit of weaving their golden silk webs—which can reach widths of up to 10 feet and often hang at about human eye level—near structures has led many people to view them as a nuisance.

“They do like to put their webs on places people go,” David Coyle, an associate professor of forest health and invasive species at Clemson University, told Backpacker in 2024. “Shelters, lean-tos. They’re probably going to be there.”

The species made its first known U.S. appearance in Georgia in 2013, likely after stowing away in a cargo ship. In the decade and change since then, their population has rapidly grown in both density and range, with sightings recorded as far north as Massachusetts. Many ecologists believe they’re likely to continue spreading: In a 2023 paper, Coyle and a group of other researchers compared the climate of joros’ home range to that of the United States and concluded that the relatively cold-hardy arachnids could eventually make themselves at home along the length of the East Coast.

While they had resided in nearby communities for at least a year prior, there had never been a sighting of a joro spider inside Great Smoky Mountains until October 2024, when Jarrett Rendon, an Americorps volunteer, snapped a photo of one in the Cades Cove area. In a post on Facebook this week, the NPS noted that while the striking spiders may not be dangerous to people, there’s evidence that they’re outcompeting populations of native orb-weavers in areas where they have become established.

To help track the spiders’ migration through the park, the NPS asked hikers who spot the spiders to log their sightings on iNaturalist, a popular app for recording and identifying sightings of plants and animals. As of the time of writing, iNaturalist showed only a handful of sightings throughout the park, including the initial observation in Cades Cove.

“Your observations will provide valuable data to help us better understand and manage this invasive species,” park officials wrote. “Together, we can protect the Smokies’ natural balance.”

What the NPS hopes to do with the data the study collects is less clear. While the agency didn’t elaborate on what other actions hikers should take if they spot a joro, Coyle noted that it’s likely too late to halt the spread of the arachnids, whose miniscule hatchlings can disperse to areas miles away by ‘ballooning’ on silk threads, and that while a kill-on-sight campaign could reduce their numbers in certain local areas, it’s unlikely to significantly drive down joros’ population as a whole.