Big, invasive Joro spiders are crawling up the East Coast

Still, people may want to watch out for the spiders’ large webs: a single Joro spider’s can be 3 feet wide, but a cluster web containing several females can span 10 feet.

Andy Davis, a research scientist at the Odum School of Ecology at the University of Georgia, said larger relatives of the Joro spider are fried “like shrimp” and sold as a snack at street markets in East Asia.

Joro spiders can survive in a wide range of conditions, he added.

“Joro spiders seem perfectly content with living on a gas station pump in addition to living in a tree in the forest,” he said.

Davis said the spiders react to stressors like noise differently than other spiders he has studied. In his lab, Davis tested the spider’s “shyness” by directing a small puff of air at it. The Joro spider responded by freezing for an hour. Many other animals, by contrast, would react more, and that tendency would make it difficult for them to live in a stressful environment long term.

But Joro spiders’ lack of reaction allows them to set up webs in surprising places, like on traffic lights above busy intersections, Davis said.

“If they can live in these disturbed areas just as much as they can live in natural areas, that means there’s nothing stopping them from living anywhere in this country,” he said.

There is no way to predict exactly when the spiders will arrive in the Northeast, since their movement is random, said David Nelsen, an arachnologist and professor of biology at Southern Adventist University in Tennessee.

“Because you’ve got the color, the size, and that element of fear, they’re really, really exciting,” Nelsen said, though he guessed “New Yorkers are not going to see this anytime soon.”

Although tales have circulated about the spiders taking flight, Nelsen said they are mostly misconstrued. The adults don’t do that, he said, but baby Joro spiders have an ability to balloon, an action Nelsen compared to when dandelion seeds get picked up by the wind. Like the seeds, the spiders get dispersed randomly based on the wind and electromagnetic currents.

“There have been reports of spiders as high as commercial airplanes, 30,000 feet in the air, being blown around,” Nelsen said.

Joro spiders of all ages may also hitch a ride on a car, unbeknownst to the driver, and end up in a new state, according to Davis.

Being relatively harmless to humans doesn’t eliminate the spiders’ threat entirely. They are invasive, and Nelsen’s research has shown that when a lot of Joro spiders live in an area for a long time, native spider populations decrease.

“There is lots of evidence to suggest that when an ecosystem loses species, which is what may be happening in this case, that ecosystem becomes really, really imbalanced and can collapse.”

Nelsen said more research is needed to determine if the Joro spiders are the cause of that decrease, however.

For now, Hormiga said, the spiders pose no scientifically documented problems for their local environment. But it will take years for scientists to understand their long-term effects.