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Spokane, Washington  Est. May 19, 1883

These giant, invasive spiders appear built to thrive in the U.S.

A Joro spider on a web with a green pine tree background.  (Mohamed Rizly/Dreamstime)
By Erin Blakemore Washington Post

Massive Joro spiders are likely to continue their march across the United States thanks to their ability to adapt to human-dominated environments, a new analysis suggests.

The spiders, which are native to East Asia, have large yellow-and-black bodies, long legs and an ability to spin orblike webs. First confirmed in the United States in 2014, in northeast Georgia, they have since spread across the Southeast.

The study, published in the journal Arthropoda, tracked their behavior in northeast Georgia; the authors argue that part of the spiders’ success in the United States may turn on their ability to tolerate busy roads.

To measure the ways in which traffic affects the spiders’ behavior, the researchers conducted more than 350 trials across 20 roads with different levels of traffic.

They touched the spiders’ webs with a tuning fork vibrating at 128 hertz, simulating prey and attempting to stimulate the creatures’ usual attack mechanism.

Overall, the spiders attacked the simulated prey 59% of the time. But spiders near busier roads were not as likely to attack as those near quieter roads.

Those near traffic attacked about half the time vs. 65% of the time among spiders with webs in lower-traffic areas.

The difference in attack behaviors suggests heavy traffic and urbanization could cost the spiders their ability to capture prey.

But when the researchers compared the body weights of urban spiders with those in less busy areas, they found that spiders living near the busiest roads didn’t weigh any less than their counterparts.

Given that there is no appreciable difference in body weight between the two groups of spiders, the researchers write, the species seems to be compensating for the often disruptive effects of traffic, perhaps by choosing larger prey.

That ability to thrive in busy urban ecosystems means the spiders will probably continue to spread, the researchers conclude.

“It looks like Joro spiders are not going to shy away from building a web under a stoplight or an area where you wouldn’t imagine a spider to be,” Alexa Schultz, co-author of the study and a third-year ecology student at the University of Georgia, said in a news release.

“I don’t know how happy people are going to be about it, but I think the spiders are here to stay.”