Joro spiders are polarizing characters.
If you live in Georgia, you’ve probably seen the giant but harmless spiders hanging between power lines or from the eaves of your home, their golden webs glittering in the sunlight.
While some find them a fascinating effect of globalization, others don’t care how they got there. They just want them gone.
But don’t grab the flamethrower just yet.
The East Asian Joro spider, officially known as Trichonephila clavata, probably arrived in the United States in a shipping container around 2013. The species is native to Japan, Korea, Taiwan and China.
Female joros have bright yellow and blue-black markings with red underbelly. They can grow up to 3 inches across when their legs are fully extended, which is similar in size to the common banana spider.
You will often see one or more smaller, brownish-red spiders hanging in the same web as a female. These are male Joros. They soar into the females’ golden web and ride in the wind on a strand of silk, says Byron Freeman, director of the Georgia Museum of Natural History and faculty member at the University of Georgia’s Odum School of Ecology. This silk is stronger and, some think, stickier than the average garden spider.
If these data are successful, the Joro female will lay up to 1,000 eggs before dying in late autumn. The spiders overwinter as eggs and hatch in spring using their silk to soar to new locations, a common spider behavior known as ballooning.
Joros are usually rather shy and will run away from you rather than try to bite. Even when they try, most of them have fangs too small to pierce human skin, according to Andy Davis, a research assistant at the School of Ecology who studies the spiders.
Do Joro Spiders pose a threat to the local environment?
In short, the researchers don’t know yet.
“It’s too early to say a thing or two,” says Davis. “A lot of people think that this spider is destroying the ecosystem, and we actually don’t think so, at least not yet.”
To the ordinary observer, it certainly seems like the Joros have been experiencing exponential growth lately, especially in the last two years. But researchers aren’t worried just yet. The spiders do not appear to have depleted local spider or other insect populations. And they are also not harmful to humans or pets.
“There is no indication that it will be invasive to the extent that it would be disruptive or economically costly,” says UGA entomologist E. Richard Hoebeke of the Georgia Museum of Natural History. “But that’s one of the reasons why we intend to study this spider a little further.
“What is its distribution in the South and beyond? How does it interact with native spiders – could it actually displace some of them, like the large garden spiders? These are some of the questions we want to explore.”
We know Joros eat stink bugs, something other local spiders don’t find appetizing. Stink bugs, a much-maligned – rightly – invasive species, don’t have many natural predators. So the Joros can be a welcome change from the annoying critters that crowd your home by the thousands. (Yes. If you see one, there are probably exponentially more hiding in the cracks and crevices of your home. Joros don’t look so bad now, do they?)
In theory, Joros could also provide a new food source for larger insects and birds.
The dewdrop spider, a species that steals its food from other spiders, seems to be a fan of its new neighbors. The spiders have been seen loitering in Joro webs in hopes of stealing their next meal.
When they’re done taking over Georgia, where will the Joro spiders go next?
Possibly the entire east coast.
Davis worked with undergraduate researcher Benjamin Frick to track Joro sightings and test the spider’s biological functions for a paper published in February. The scientists found that the species has a high metabolism, high heart rate and high resistance to cold.
This suggests that Joros can probably exist beyond the borders of the southeast. Also, the east coast is at similar latitudes as the spider’s homeland of Japan, another indication that the species could be spreading.
“The potential for these spiders to be spread by human movements is very high,” says Frick. “Just before we published this study, we anecdotally received a report from a UGA graduate student who accidentally transported one to Oklahoma.”
What can we do against the Joro spider?
Davis and Frick suggest that we learn to live with the new way because it’s not going away anytime soon.
One thing people can do is report sightings to help researchers track the spread of the species.
“The best thing we can do when introducing a new, non-native species is to catch it in the early stages,” says Chuck Bargeron, director of the Center for Invasive Species and Ecosystem Health. As the UGA Cooperative Extension and Outreach Center, the center is housed jointly within the College of Agricultural and Environmental Sciences and the Warnell School of Forestry and Natural Resources.
“We encouraged people who see a Joro spider to take a picture of it and report it via EDDMapS,” he continues. “This helps us track the species’ spread over time.”
EDDMapS is one of many apps and websites developed by the center that allow citizen scientists to contribute to the mapping and tracking of alien species.
What doesn’t help is spraying pesticides and squashing spiders left and right. Sure, you’ll kill individual spiders, but they’ll just be replaced with new ones.
“Spraying too many pesticides for something that might not even be a problem affects other species and isn’t the answer,” says Bargeron. “This is because humans are afraid of spiders, so they kill the spider when they see it. Pesticides just aren’t the best way to deal with these spiders.”
Such resistance is futile anyway. The Joros are really unstoppable – with pesticides, a shoe or a blowtorch. The spiders are here now, making the best of their situation.
“People are at the root of their invasion,” says Frick. “Don’t blame the Joro spider.”