New study finds Joro spiders spreading quickly in eastern U.S.

David Coyle found a Joro spider in his backyard. PHOTO: DAVID COYLE

A new, peer-reviewed study at Clemson University finds that Joro spiders (Trichonephila clavata) are here to stay.

About three years ago, Dr. David Coyle, a scientist and assistant professor in the Department of Forestry and Environmental Conservation at Clemson University, first spotted what he believed was a Joro spider in his backyard. After quickly confirming the species, he did what any inquiring mind might: He began collecting data.

“I walked the edge of the woods — and they were everywhere,” Dr. Coyle said in the news release. “I have a 94-yard perimeter and found 50 Joro spiders on the perimeter. So, basically, every two yards there was a spider. This was in the morning and all the webs had dew on them, so you could easily see them, and there were just dozens of them on the power lines across the road.”

Dr. Coyle needed much harder evidence than that initial observation to assess how pervasive the Joro — a large yellow spider with a yellow-and-gray abdomen — had, and could, become.

In a new peer-reviewed study, Dr. Coyle and his collaborators shared the results of their evidence-gathering with one big takeaway: Joro spiders are here to stay and are spreading like wildfire.

The study used advanced modeling techniques, based on 20 separate variables, to assess the Joro’s native range and then applied those variables to the entire United States in an attempt to quantify habitability elsewhere.

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

Southern Adventist University Professor Dr. David Nelsen, who led the research in Peachtree, Ga., pointed to another major takeaway: The study shows native species are negatively affected by Joros. This means more research is needed to ascertain why — and what can be done about it.

And if the conclusion that a large area of the eastern United States may be habitable to Joros is true, Dr. Nelsen said, it may present a major challenge for native species and further stress already-fragile ecosystems.

“Because of how far Joros have already spread and how fast they continue to spread, collaboration is vital for a project like this to succeed — both across institutes and with local communities,” he said. “I consider it one of our greatest successes that we have been able to assemble a team spread across the southern United States and partner with several non-academic groups and individuals.”

Dr. Coyle reports he didn’t see a Joro with his own eyes until 2020, in Clemson, S.C.  The non-native species was first found in northern Georgia in 2014. Known to scientists as Trichonephila clavata, the Joro is now present in the Upstate and parts of the Midlands in South Carolina.

T. clavata’s range is estimated to span at least 120,000 square kilometers, occurring across Georgia, South Carolina, North Carolina and Tennessee. Sightings have also been reported in Alabama, Maryland, Oklahoma and West Virginia.

The Joro spider’s pattern of spread suggests it is primarily driven by natural dispersal mechanisms, such as ballooning, a process by which 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. Human-mediated transport cannot be discounted, however.

Like other large-bodied orb-weavers, Joros capture and feed on flying insects and potentially other small animals. Because they are spreading across both natural and urban habitats, management options are limited. In fact, initial reports suggested the species was beneficial because it eats brown marmorated stink bugs and other nuisance species. The displacement of native species, however, has overshadowed the benefits.

“These spiders don’t seem to care what gets in their web,”  Dr. Coyle said. “They’re just as likely to eat brown marmorated stink bugs as they are to eat a Monarch butterfly. 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. It’s six of one or half-dozen of another — it’s the same thing to that spider. It’s prey.”

While the exact mechanisms of their spread are still being studied, he added, one pattern is quite clear: Where you have an abundance of Joro spiders, you find fewer other species.

“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,” Dr. Coyle said. “Are they bad or good? It’s very nuanced, depending on your perspective.”