Ecologists Andrew Davis and Benjamin Frick have crisscrossed the United States studying everything from monarch butterflies to house finches. But when a giant, neon-yellow spider arrived in the U.S. state of Georgia, the team got to observe a fascinating invasive species from their own backyard.
“It’s hard not to get interested in such a Nerf football-looking spider when it’s in your face that often,” says Frick, who at one point had 10 invasive jorō spider webs draping the trees outside his apartment.
Since Trichonephila clavata's accidental introduction in 2014—likely via a container ship from East Asia to Atlanta—the palm-size arachnid has spread across Georgia and into the neighboring Carolinas, as well as parts of Tennessee and Oklahoma.
With the jorō spider spinning across the country unchecked, Davis and graduate student Benjamin Frick, both at the University of Georgia, wanted to know what, if anything, would stop its northward expansion. For instance, freezing temperatures had stymied a closely related invasive spider species, the golden silk spider, T. clavipes, from inching much farther north than metro Atlanta.
Their laboratory experiments revealed, however, found that jorō spiders readily tolerate freezing temperatures, indicating that the species could potentially spread as far as New England.
“People around the U.S. are probably going to start seeing more of these spiders,” says Davis, whose results were published recently in Physiological Entomology.
Though there are no solid population estimates of the non-native arachnid in the U.S., Richard Hoebeke, an entomologist for the University of Georgia Extension, has fielded a steady increase in questions about the species since 2014. The long-legged, teal-striped females weave webs several feet wide across trees and porches, which, combined with their four-inch-wide bodies, make them hard to miss.
For an unknown reason, 2021 was a banner year for the jorō spider. That “year was just crazy. I had in excess of 500 emails from the public from August to December,” says Hoebeke, who was not involved in the new study.
Despite the females’ startling colors and size (males are smaller and brown) the spiders are harmless to humans, Hoebeke stresses, with fangs too short to break our skin. Like many orb-weavers, jorōs are also passive hunters, waiting for insects to get caught in their nets.
Likewise, there’s no evidence—at least yet—that jorō spiders will upset the ecological balance in places where they live. For that reason, state agricultural agencies do not recommend killing the arachnid on sight.
In Japanese mythology, this species is considered a deceptive shape-shifter that preys on young, handsome men—hence its name jorō-gumo, which means "binding bride" or "whore spider." In Korea, the arachnid's name is mudang gumi, which translates to "shaman" or "fortune-teller" spider.
The species has likely established itself successfully in Georgia for a few reasons: For one, it suspends its webs high up, "a niche that is not filled by a lot of other native spiders, which tend to be closer to the ground,” Davis says. (Learn more about the wonders of spiderwebs and silk.)
“Their webs are like aerial traps that work like holding a net up high in the air, like we would use a butterfly net to catch flying insects,” explains Paula Cushing, an arachnologist at the Denver Museum of Natural Sciences who wasn’t involved in the study.
What’s more, pollution and habitat loss in parts of Georgia may have reduced numbers of endemic spiders, allowing the non-native species to move in more easily, says Hoebeke.
“When you remove native species or treat your grasses and agricultural fields with pesticides and herbicides, you are imposing an imbalance that can create open niches,” he says.
A hardy invader
For their experiment, Frick and Davies collected 35 wild female jorō and 22 wild female golden silk spiders from two locations: around the University of Georgia campus in Athens and in Savannah, about two hours southeast.
The scientists then brought the arachnids back to their lab and placed each one in a small, sealed container. Next, the team recorded how quickly oxygen levels in the container dropped, which is a measure of the animal’s resting metabolism. For a spider to survive cold temperatures, it must be able to increase its resting metabolism to keep its body warm. Indeed, the results showed the jorō spiders’ metabolism was twice as high as that of the golden silk spiders.
Davis and Frick also measured the spiders’ heart rates, watching the subtle physical pulsing under the microscope. Not surprisingly, the jorō also had a faster pulse, reflecting its more rapid metabolism. (See 10 beautiful photos that will make you love spiders.)
Then, the team placed a separate set of female spiders (27 jorō, 20 golden silk) into a freezer for two minutes. Only half of the golden silk spiders survived, compared with 77 percent of the jorōs.
This data, combined with the jorō spiders ability to mate and reproduce more quickly than the golden silk spider, suggests the species can withstand northern U.S. winters.
“The jorō spider is here to stay,” Frick says.
Cushing says the study is important in understanding the potential future range of the jorō spider in the U.S., since it outlines key environmental parameters the spiders can (and can’t) tolerate. But she draws the line at using these results to make solid predictions as to where the spider will go.
“We’re just not there yet,” Cushing says.
Jury still out on the jorō
Meanwhile, what the jorō’s expansion means for U.S. ecosystems is unclear. Cushing hasn’t heard any reports of jorōs displacing native spiders, nor does she know if they’re outcompeting other spiders for prey.
The jorō could even provide some benefit, Cushing says, if the jorō can eat agricultural pests; for instance, there are some observations of the spider eating brown marmorated stink bugs, another non-native insect. (Read why not all non-native species are bad.)
Davis also notes that the jorō appears to be moving southward much more slowly compared to its northerly march. Although he doesn’t know why that might be, he theorizes it could be due to stronger competition with other spiders in warmer climes.