Invasive Joro Spiders Continue to Spread

It’s a type of flailing yard ballet in Georgia these days.

Homeowners and walkers swing their arms repeatedly, wielding long sticks and brooms high in the air while they mutter or shout obscenities. Walkers step along rhythmically until something breaks their stride. Then they hop around, swiping at their faces or arms.

The cause of all this angst? Joro spiders.

Joro spiders (Trichonephila clavata) are native to Asia with their range extending from northern India up into Korea. The name comes from the Jorogumo, a mythical creature from Japanese folklore that shapeshifts from a giant spider into a beautiful woman to ensnare young men.

The invasive species first arrived in Georgia about a decade ago. They likely hitched a ride on a shipping container through international commerce. They’ve been more apparent the past few years, particularly in early fall when their webs are bigger and harder to miss, says ecologist Byron “Bud” Freeman, director of the Georgia Museum of Natural History.

Their webs are impressive three-layer creations that are incredibly elastic and hardy. In the center, is a main basket-shaped orb sandwiched by two more webs in the front and back. When sunlight hits the strands, the web has a bit of a golden glow.

Female Joros are also very colorful. Mature females are bright yellow with dark blue stripes and red marks underneath. The females can be as large as almost 3 inches across with legs fully extended.1(Male Joros are much smaller and drably colored.)

Imagine going face-first into a web and encountering its resident.

Although no one likes some webbing across the face, not everyone thinks the spiders are a nuisance.

“Some people really like them. They say these are gorgeous spiders and they’re enjoying watching them,” Freeman tells Treehugger. “It’s a divide, like politics. Some people like them and some people don’t.”

Freeman is captivated by the creatures and has been looking at where they might end up next and what impact they could be having on the ecosystem.

Joros were first spotted in Braselton, Georgia, then slowly began to spread throughout the state. They probably hitchhiked on traveling vehicles. Now they’ve spread into neighboring South Carolina and Tennessee.

The spiders have gone maybe 100-150 miles in about a decade, Freeman figures. So it will likely be a slow migration, but eventually, the arachnids could spread throughout the East Coast.

“We have one example of a spider on the side of a giant shipping container in Tacoma, Washington. The other smoking gun is people open their cars and see them under the hood or attached to a bumper,” Freeman says.

A grad student from the University of Georgia reportedly accidentally transported one to Oklahoma. Another student drove about 300 miles to North Carolina and, upon arrival, noticed a Joro in its web on the bumper of his vehicle.1

Researchers have been plotting the sightings and slow migration. They’ve noticed a couple of the spider stragglers in various states, but so far only Georgia, Tennessee, and South Carolina have established populations.

A study released earlier this year by UGA researchers compares the Joro to a relative, the golden silk spider, which first migrated to the Southeast from the tropics more than 150 years ago. The golden silk spider hasn’t been successfully spreading farther away because it is vulnerable to cold temperatures.

The study found, however, that the Joro has about double the metabolism of the golden silk spider with a 77% higher heart rate. They also survive better in a brief freeze.

The findings suggest that Joros would be able to exist outside the Southeast.3

Researchers are not yet sure what impact these invasive insects are having (or could have) on the ecosystem.

Last year, researchers began cataloging the items the spiders trapped in their webs. They noted that they will take yellow jackets, brown marmorated stink bugs, and modest-sized bees including honeybees and bumblebees.

Freeman says they’ve noticed fewer insects overall this year and they’ve found that Joros are generally smaller than last year. He wonders if there is a connection.

“It’s totally not based on anything because I don’t have good comparative data, but what if these things are telling us something? It seems that they’re skinnier this year and you can change the size of a spider by feeding it a lot,” Freeman says. “What if they’re a harbinger of pockets of decline in the abundance of insects?”

Freeman and his colleagues will continue to monitor Joros and their webs and see what effect they might have on the species around them.

He has had reports of feathers being found in a web. He’s not sure if a bird accidentally flew into a Joro creation or if it did a fly-by hoping to nab a spider or some of its trapped prey.

“We might see more of that as birds learn they are tasty,” Freeman says.

In general, the spiders don’t want anything to do with people. If confronted, their first move is to scamper away. If you cornered one or tried to hold it, they could react.

“They have some formidable-looking fangs. They’re not tiny, but it’s not a giant northern hornet that could really sting you,” Freeman says. “Every spider has venom to subdue prey. They’re not especially venomous to us.”

Original Article

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