As the invasive Joro spider becomes common in the Chattanooga area, preliminary research from a local university shows the East Asian spider's range could expand all the way into Southern Canada and take over habitat from native spider species.
The range of the Joro spider has been expanding rapidly throughout the Southeast, according to David Nelsen, a biology professor who's been conducting research on the species at Southern Adventist University, and the effect has been seen on the university's Collegedale campus.
As he was being interviewed by phone, Nelsen hiked around one of the two forested ridges that flank the campus looking for Joro spiders.
"Two years ago, we found one spider on both ridges, and that was the only sighting we had on campus," Nelsen said of 2021 sightings. "Last year, we found two to three within the Collegedale area, and this year, we're at 15 on one ridge. And we haven't even gotten to the other ridge yet."
Regionwide in 2021, Joro spiders were found in Fort Oglethorpe, off Battlefield Parkway; near Cravens House on Lookout Mountain; on Signal Mountain; as well as the one on campus.
Last year, about 20 Joro spiders were identified in the Chattanooga area — and many sightings had both a male and female in the web, Nelsen said.
"That's a pretty good sign that they're breeding now, and they're not just getting blown in anew every year, that they have a stable population in our area," Nelsen said.
Joro spiders expand their range through ballooning, meaning they produce a special kind of silk that allows them to build a parachute-like structure and travel by wind as juveniles, Nelsen said. Once landed, males and females both build a web, and later in the season, the males leave their web to find a female.
First discovered in Atlanta in 2014, Joro spiders are thought to have come to North America accidentally by shipping containers, the University of Georgia has reported. The spiders aren't harmful to humans, and up until now it's been too soon for researchers to know their impact on the local ecology.
Nelsen said he had a manuscript titled "Veni, vidi, vici? Future spread and ecological impacts of a rapidly-expanding invasive predator population" accepted by the journal Ecology and Evolution detailing the recent research at Southern Adventist. Currently in the review process, he is one of six authors of the article he expects to be published in about two months.
"The longer they've been there or the closer you are to where the invasion started, there's decrease in biodiversity," Nelsen said about Joro spiders' impact on native orb spiders.
Balance of species
Realistically, there's not much that can be done about Joro spiders because any attempts at using insecticides would also kill native species, Nelsen said. The best case scenario is that a balance is found with native species, he said, if predators start to see Joro spiders as a food source.
Based on Joro spider's habitat preference in East Asia, Southern Adventist researchers found the species will survive in the Midwest, the Great Lakes region and into Southern Canada. Surprisingly, Georgia is a poor location based on the models — yet the spider still thrives there, Nelsen said.
"In Georgia, where the invasion started, it's the most common spider you're going to see," he said. "They're everywhere, and you have a hard time seeing other things."
Last year was a banner year for range expansion, and Nelsen said there were sightings in Virginia, West Virginia and Maryland. Some Maryland sightings had both male and females in their web, he said, leading some researchers to think that there was a second point of invasion in Maryland, with Baltimore being a port town.
There was one sighting in Nashville last year, but none in Knoxville, Nelsen said.
Earlier in the season, Nelsen encouraged residents to report Joro sightings to iNaturalist, an online community of citizen scientists and naturalists sharing observations of biodiversity.
Even at 85-years-old, Paul Shelton stays busy growing a variety of plants at his home on Chickamauga Lake in Chattanooga's Lake Shore Estates. Recently, he found a Joro spider in the yard of his son, who lives next door.
Shelton first noticed the thick gold strand of web, about as thick as yarn — and bright gold in the sun, he said. The gold web strand was attached to a tree about 18 feet above an azalea bush at his son's house next door.
Attached to that main web strand were other anchoring web strands, centered around a 2 foot by 2 foot web and the palm-sized spider that built the entire structure.
"Look at this web up here, look at that line," he said, pointing upward. "It's gold. And when the sun's on it, it just shines, man. It's just like a golden thread."
Shelton has been interested in ecology and animals his whole life, he said.
Only mature Joro spiders make the golden web — earning the common name Golden Orb Weaver, Nelsen said.
"The gold is unreal, and you don't notice it until you get a lot of it together," Shelton said of the spider's thick web. "It must've run up and down that line a hundred times."
Contact Andrew Wilkins at [email protected] or 423-757-6659.