Researchers analyzed the stomach contents of more than 200 Joro spiders from 33 sites across Georgia and South Carolina for the new study. (Photo by Dorothy Kozlowski/UGA)
Scientists Just Tested One of the Biggest Fears About Invasive Joro Spiders
In A Nutshell
- A new study tested Joro spider and native spider gut DNA to see whether the invasive spiders are eating native species’ food supply.
- Joro spider diets included roughly 206 types of prey, the widest variety in the study, with at least 26 prey types found in no other species.
- Overall diet composition differed between Joro spiders and three native orb-weavers by 10 to 25 percent, while the native species differed from each other by no more than about 7 percent.
- Native spiders living near Joro spiders ate diets similar to native spiders with no Joro spiders around, suggesting the invader isn’t forcing locals onto a different menu.
Joro spiders have spread across Georgia and South Carolina fast enough that their webs, some the size of car doors, are now a common sight strung between porch railings and tree limbs. The palm-sized traveler from East Asia first turned up in Georgia in 2014 and hasn’t slowed down since. As it spreads, one question keeps coming up: is it eating native spiders out of house and home?
A new study in PLoS ONE offers a hopeful answer, at least for now. Researchers collected hundreds of spiders from dozens of sites in Georgia and South Carolina, then tested their gut contents for leftover DNA to see what each spider had recently eaten. The results push back against the idea that Joro spiders are muscling in on the same meals native orb-weavers rely on; instead, the newcomer seems to be working a different menu altogether.
That doesn’t mean the two groups never cross paths at the dinner table. Joro spiders and native web-builders share some prey, since they’re all catching whatever flies into their silk. Whether that shared menu adds up to real competition, though, is a separate question.
Spiders Liquefy Their Prey, So Scientists Read the DNA Left Behind
Spiders don’t leave chewable leftovers behind. They liquefy their prey and drink it, so researchers can’t pick out bug parts under a microscope. Instead, the team used a technique called DNA metabarcoding, identifying traces of the prey each spider had recently eaten.
Between early and late October 2021, researchers walked the edges of 52 sites in Georgia and South Carolina, hand-collecting female spiders from their webs. They gathered 213 Joro spiders along with several native web-building species. Sample sizes for some natives were too small to draw firm conclusions, so the team focused its comparison on three species with strong representation: the spotted orb-weaver, the marbled orb-weaver, and the spinybacked orb-weaver.
Back in the lab, researchers pulled the gut from each spider, extracted its DNA, and ran it through machines that scan millions of genetic fragments at once, using a chemical trick to suppress the spiders’ own DNA. The team ended up with solid data covering 164 different types of prey across all four species, most of them small flies.
Joro Spiders Eat Dozens of Prey Types Native Spiders Never Touch
Joro spiders came out on top for variety, with an estimated 206 types of prey, by far the widest spread in the study, though that’s partly because researchers collected more Joro spiders than any native species.
A more telling result came from comparing diet makeup directly. Joro and native diets were clearly distinct, while the three native species’ diets looked more like each other than like the Joro spider’s. Joro diets differed from native diets by roughly 10 to 25 percent, while the native species differed from one another by no more than about 7 percent. A closer look turned up at least 26 types of prey found in Joro guts and nowhere else in the study. The marbled orb-weaver had six unique prey types, the spotted orb-weaver had one, and the spinybacked orb-weaver, the smallest species studied, had none.
Researchers also calculated an overlap score for each species pair, running from zero, no shared food, to one, identical diets. Counting whether a prey type appeared at all, Joro spiders and native species scored around 0.6. Calculating overlap by how much prey DNA actually showed up produced lower estimates.
A more reassuring result involved native spiders living alongside Joro spiders compared to those that weren’t. If Joros were forcing natives onto a different menu, that pressure might show up at shared sites. Researchers didn’t detect one: native spiders alongside Joros had broadly similar diets to natives where Joros weren’t recorded. The researchers wrote that the invader’s presence “did not significantly impact diet composition.”
Behavior and Web Placement, Not Just Prey, Set Each Species Apart
Study authors point out these four species behave differently even though they all build round webs in similar spots. Joro spiders sit brightly colored at the center of huge gold webs and tend to freeze rather than flee when disturbed, a pattern that may draw in certain insects. The marbled orb-weaver is also colorful but retreats from disturbance, and what it catches ties closely to how high it builds its web. Small differences like these, in behavior, web placement, and silk properties, could steer each species toward a different set of meals within the same patch of forest.
Researchers call this an early step rather than a final word. Diet overlap is only one way an invasive species could squeeze out natives; web fights, predation between species, or crowding are separate possibilities not measured here.
Joro spiders aren’t going anywhere, and their range is expected to keep growing. What stands out here is that one specific fear behind a lot of the headlines, that these spiders are strongly competing with native spiders for food, didn’t get much support.
Paper Notes
Limitations
The researchers note several caveats to their work. Native spider sample sizes were relatively small compared to the Joro spider samples, which limits how confidently total diet richness can be estimated for native species and may mean additional unique prey types remain undetected. The DNA method used measures presence or absence of prey rather than how much of each prey item was eaten, so the diet overlap figures are based on whether a food type showed up at all, not how important it was to the spider’s overall intake. Despite using primers designed to minimize spider DNA, a large share of sequencing reads still matched spider DNA rather than prey DNA, which the team addressed by removing those reads before analysis. The researchers also note that because the DNA method is extremely sensitive, some detected prey could reflect secondary feeding events rather than direct consumption, and they were unable to distinguish between the two. Finally, the study captured a single autumn window in one region, and the authors stress this is an initial look at diet patterns rather than a complete picture of competition, since factors like web placement and space competition were not directly measured.
Funding and Disclosures
According to the paper, the authors received no specific funding for this work, and the authors declared that no competing interests exist.
Publication Details
The study, titled “DNA metabarcoding to estimate diet overlap between the introduced Joro spider (Trichonephila clavata) and three native orb-weaving spiders,” was written by Erin E. Grabarczyk of Valdosta State University and Jason M. Schmidt of the University of Georgia. It was published in PLoS ONE in 2026 (volume 21, issue 6, article e0351929). DOI: 10.1371/journal.pone.0351929.
