A giant East Asian spider is hitching rides on cars out of Georgia into neighbouring states

The Joro spider, a palm-sized orb-weaver native to East Asia, has been riding vehicles out of its original Georgia foothold and into Tennessee, South Carolina, North Carolina and beyond since researchers first confirmed it near Braselton, Georgia around 2010. The Georgia Museum of Natural History’s arthropods collection manager, E. Richard “Rick” Hoebeke, has tracked the spread using records submitted to the museum and logged on iNaturalist, and by 2022 that evidence placed the species’ range into extreme southern Tennessee and northwest South Carolina. Dispersal happens two ways at once: ballooning, in which spiderlings release silk threads and ride wind currents, and vehicle hitchhiking, in which the spiders or their egg sacs travel attached to cars driving between states.

Clemson University researchers pushed the range estimate further in a peer-reviewed study current as of October 2022, putting the spider’s confirmed territory at roughly 120,000 square kilometers across Georgia, South Carolina, North Carolina and Tennessee, with additional reports already logged in Alabama, Maryland, Oklahoma and West Virginia. David Coyle, the Clemson forestry and invasive-species researcher who led the modeling work, said the spider’s native comfort range lines up closely with conditions across much of the eastern United States, meaning the current four-state core is a floor rather than a ceiling.

A Decade-Old Georgia Population Became a 120,000-Square-Kilometer Range

The species’ formal scientific record dates to a 2015 paper by Hoebeke, W. Huffmaster and B.J. Freeman describing it as newly found in North America, but the museum’s own field evidence suggests the Joro had already been established around Braselton for roughly five years before that publication. That gap between quiet establishment and formal detection is common with small, web-building invasive species, since a spider spinning webs in suburban trees rarely draws official attention until its population becomes large enough to notice. By the time Clemson’s team ran its 2022 range model, the spider had gone from a single Georgia county to a four-state footprint spanning more than 46,000 square miles.

The Clemson study used 20 separate environmental variables drawn from the Joro’s native Asian range, then applied those variables across the United States to estimate where the species could plausibly survive. “Those data show that this spider is going to be able to inhabit most of the eastern U.S.,” Coyle said, a conclusion the study’s authors reached by matching climate and habitat conditions rather than by projecting the spider’s current spread rate forward in a straight line.

Cars, Not Just Wind, Are Carrying the Spider Across State Lines

Ballooning explains how a spiderling crosses a few miles on its own, but it does not explain how the species jumped from a handful of Georgia counties into Maryland and Oklahoma within roughly a decade. Vehicle hitchhiking closes that gap: an adult spider or an egg sac attached to a car, truck or trailer can travel hundreds of miles in a single trip, seeding a new population far outside the reach any wind current could carry it. The Georgia museum’s tracking page lists both mechanisms side by side as the drivers of the observed range expansion, without ranking one above the other in importance.

That combination — short-range wind dispersal filling in a region once a population establishes, long-range vehicle transport seeding new regions entirely — is why the Joro’s map has grown in scattered outlying points as often as in a smooth expanding circle. A single hitchhiking spider reaching a new state can found a population well ahead of where ballooning alone would have carried the species by that date.

Native Orb-Weavers Thin Out Wherever Joro Numbers Climb

Coyle’s research team found a consistent pattern once Joro numbers rise in an area: native spider populations fall. “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,” Coyle said, pushing back on an early public theory that the Joro was a net benefit because it eats invasive brown marmorated stink bugs. Southern Adventist University’s David Nelsen, who co-led related research into the species, said the ecological question is less settled than the human-safety one and needs further study to pin down the exact mechanism behind the native-species decline.

What the spider eats along the way is indiscriminate. A large-bodied orb-weaver of the Joro’s size will catch and consume whatever lands in its web, from invasive stink bugs to rare native pollinators, which is why researchers stop short of calling the species’ arrival either good or bad for a given ecosystem — it depends entirely on what else happens to be flying through that particular yard.

A Bite Study Found the Spider Barely Hurts, and Spraying It Rarely Helps

The uncertainty over ecological impact does not extend to how dangerous the spider is to people. A separate bite study Nelsen led found that Joro spiders overwhelmingly try to flee contact rather than bite, and that induced bites on volunteers scored no higher than a 4 on the pediatric Wong-Baker pain scale, with most in the 1 range comparable to a mosquito bite. Labeled insecticides kill Joros effectively, and household substitutes such as bleach, hair spray and dishwashing detergent tested by Coyle’s team worked too, though Coyle warns against using them: “They are not labeled as insecticides, therefore it is illegal to use them as such.” He recommends physically relocating a Joro with a broom or stick over spraying one at all.

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This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.