Field Museum

Will Giant Joro Spiders Invade Illinois? Here's What One Scientist Says

Individual Joro spiders "may occasionally" be found in Illinois, according to a Chicago scientist

Giant, flying Joro spiders invaded Georgia late last year, unnerving some with their golden webs. And according to researchers, many more Americans may get a glimpse of the enormous spiders as they could spread to much of the East Coast.

According to a study from the University of Georgia, Joro spiders are found in much of Japan, which has a similar climate to the U.S.

“Just by looking at that, it looks like the Joros could probably survive throughout most of the Eastern seaboard here, which is pretty sobering,” study co-author Andy Davis, said in a statement.

But could the spiders feasibly thrive in the Midwest, including Illinois?

While they may appear in the region, scientists say an invasion is unlikely.

The reason: summers are too short, according to Petra Sierwald, associate curator of the Negaunee Integrative Research Center at the Field Museum in Chicago.

Sierwald explained the Joro spider has a one-year life cycle in Japan: hatch from a cocoon in the spring, feed, mature in the fall, and then the mother dies, leaving a cocoon behind.

Illinois typically sees warm weather between May and October, and that may not be enough time for Joro spiders to catch enough prey to get a large body, she explained.

In order to thrive, the Joro would need to change its life cycle: hibernate as a teenager once and mature in the second year.

Unlike the East Coast, which typically experiences a mild spring, it's typically colder in Illinois. However, individual Joro spiders "may occasionally" be found in parts of the state, Sierwald stated.

"But I doubt they will be able to establish reproductive, stable populations and mature as a sort of mother (after laying eggs) in the fall of the 2nd year," she explained.

The Joro is part of a group of spiders known as orb weavers for their highly organized, wheel-shaped webs. Joro females have colorful yellow, blue and red markings on their bodies and can measure three inches across when their legs are fully extended.

It’s not clear exactly how and when the first Joro spider arrived in the U.S. or why they were so abundant in Georgia last year.

Their impact on native species and the environment is also not clear, though some researchers believe they are benign.

NBC Chicago/Associated Press
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