The Invasive 'Fortune-teller' Joro Spider Is Getting Cozy in the U.S.

By: Allison Troutner  | 

joro spider
A Joro spider (Nephila clavata) hanging out in Kitanomaru Park, Chiyoda-ku, Tokyo, Japan. Wikimedia Commons (CC BY SA 4.0)

An invasive species of spider is making itself comfortable in parts of the southern U.S. But don't let the Joro spider give you the creepy crawlies just yet. Between its golden webs and its Tarzan-esque silk swinging tactic to track down a mate, this arachnid is a fascinating and, as far as we know, harmless (unless you're a stink bug) addition to the ecosystem.

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The Beautiful Binding Bride

The Joro spider, scientifically known as Nephila clavata is native to East Asia. In Japan, it's called jorō-gumo meaning "entangling or binding bride." In Korea, it's called mudang gumi meaning "shaman" or "fortune teller" spider. The names reflect the beauty and intrigue of this orb-weaver. While the smaller drab males are nothing to write home about, the females feature yellow and bluish-green bands across the body, orangish bands on the spanning legs, and a bright red underbelly. This spider can't actually tell your fortune, but she can weave a beautiful basket-shaped web that reflects gold in the sunlight.

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Globalization for Spiders

Along with electronics and bananas, exotic plants and critters like the Joro spider are known to hitchhike on America-bound commodities, especially in shipping containers. Now, the Joro exists 25 counties in Georgia and parts of South Carolina. In some cases, homeowners have hundreds around their homes. They prefer to make their webs high in trees and have been found in forests, urban woods, porch lights, wooden decks, bushes, tall weeds and even on the vinyl siding of homes.

Their ability to adapt to natural habitats and food sources in Georgia and South Carolina has allowed their numbers to swell. However, it's only a matter of time before predators catch up with the new resident. "I think that the spiders have spread so quickly here because predators, parasites, and diseases have not caught with them yet," says Professor Paul Guillebeau, professor of entomology at the University of Georgia. "If there is a new, large food resource like the booming spider population, something will take ultimately take advantage," he says.

It's just a matter of time before birds or parasitoid wasps figure out there's a new meal in town.

	joro spider
A Joro spider enjoys a ladybug for dinner in Jeollanam-do, South Korea.
Wikimedia Commons (CC BY SA 3.0)

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Tarzan and Joro

Joro spiders tend to build webs close to each other, which helps the mating process, since males don't make their own webs, a function that is left to the females. To mate, males must pursue females, albeit carefully. They may use gossamer and float on a breeze from tree to tree until a female is within sight, or they spot a less male-occupied web.

It's kind of cute to think of this spider as a little Tarzan swinging from tree to tree to find his Jane, but that's where the romanticism ends. If a male spider isn't careful, he may become dinner instead. "The male will make a little web and deposit sperm there and then suck up the sperm in structures (pedipalps) near the mouth," says Guillebeau. "Then the male tries to find a receptive female. The males are almost always smaller, so it's tricky business to make your move without being eaten." Guillebeau sees males around his house wait until a female is busy eating an insect before he approaches — a safer approach.

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They're Big, but Not Bad

Though the Joro spider was first spotted in Georgia in 2013, it's still too early to understand its big-picture impact on the environment. So far, however, they seem to be thriving on a diet of brown marmorated stink bugs and other flying insects, which is appreciated by farmers whose crops can suffer from stink bug infestations. As orb weavers, they will naturally compete with other orb weavers for prey, but since they often weave their webs higher than other spiders, they may be catching different kinds of prey, notes Guillebeau.

Joro spiders are venomous, like all spiders, but they aren't dangerous to you or your pets and will only bite if they are scared enough to do so. "Even if you walk into a Joro web, it will try to escape rather than attack you. If you catch a Joro in your hand, it may bite you out of fear. If I were caught by a giant, I'd probably bite," says Guillebeau. If you do get bitten, you may be a bit uncomfortable but it's not as bad as a brown recluse or black widow.

What should you do if you see one? You may be tempted to kill it, but instead try being more curious, Guillebeau suggests. "Have a look at it every couple of days. Show your children; they are fascinating to watch. Toss an insect into the web if you want to see them in action." Guillebeau reminds us, "Don't kill spiders (or anything else) for no good reason. We are all playing our role in the ecosystem."

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