They're Big! They're Spreading! Should We Be Afraid of Joro Spiders? Experts Weigh In

·5 min read

What is that monster-sized spider?

Joro spiders might seem scary, especially to the arachnophobe. These very big spiders, (also known in science as trichonephila clavata), can grow up to three inches or even the size of a palm. Their legs and abdomens have brightly colored yellow and black stripes. There is red on their underbelly, and they weave giant golden webs the color of golden silk.

In other words, the Joro spider seems otherworldly—the stuff of science fiction. And these eight-legged creatures are spreading out!

Related: The 15 Biggest Spiders in the World

In February, Physiological Entomology published a study that these arachnid, which have been mostly found in southeastern states, have been on the move. Experts report that because they can survive in colder climates they may be stretching their proverbial legs and inhabiting more of the southeast.

But fear not! These spiders are considered harmless. Don’t let those headlines fool you. ”Spiders are harmless to humans, except for very rare circumstances, and most of what you hear about them in the news is incorrect or untrue,” says Dr. Shahan Derkarabetian, a biologist researching arachnid diversity and evolution at the Museum of Comparative Zoology at Harvard University. “The vast majority of the articles you are seeing about this spider exaggerate and fear-monger, with a tendency toward click-bait titles.”

Here’s what we know about Joro spiders.

What are Joro spiders?

The Joro spider, (aka trichonephila clavata) has roots in East Asia and is considered a tropical orb weaver, which means they are found in tropical areas. “The Joro spider is a ‘cousin’ of our golden silk spider (or banana spider), trichonephila clavipes, that is common in the southeastern United States,” says Professor Anne Danielson-Francois, PhD, from the University of Michigan, Dearborn, who specializes in the behavioral ecology of spiders.

What does the name “Joro” in Joro spider mean?

“The name Joro originates from Jorōgumo, a yōkai or mythical creature from Japanese folklore,” says University of Cincinnati biologist Nathan Morehouse, who is director of UC's Institute for Research in Sensing. “Jorōgumo are shapeshifting spiders that can turn into beautiful women to ensnare and eat young men. The name in modern kanji translates literally to “entangling bride.”

Related: How Do Spiders Survive in Basements?

What makes Joro spiders so scary?

The Joro spider is big, very big. “Including its legs, the spider is around 3-4 inches long, about the same size of our indigenous argiope (or black and yellow garden spider). And trichonephila (known as the golden silk spider or banana spider),” explains Danielson-Francois. She also adds that despite their dramatic appearance, they are not dangerous and even are helpful to us. “There is nothing to fear from these spiders,” she says. “They are gentle and serve as free pest control.”

What do Joro spiders do?

“Joro spiders are docile animals concerned mostly with catching insects in their webs or finding mates,” says Dr. Morehouse. “But they are large, much larger than the spiders we are accustomed to here in the United States. So for those who are arachnophobic, these spiders are alarmingly large.”

Also, as Morehouse explains these spiders weave big webs. "Their webs can also be quite big, strung between tree branches or across pathways, and the silk strands must be strong enough for this larger web size. So getting tangled in one of these webs can be an unpleasant surprise,” says Dr. Morehouse. “The good news is that these spiders are not interested in indoor spaces, and the strands of their webs are golden, making them easier to see. The spiders themselves are also not aggressive. However, if mishandled, the spiders may bite out of self-defense, and the bites are painful like a bee or wasp sting. So if they scare you, the best idea is to simply give them plenty of room.”

Is there a difference between female and male Joro spiders?

“Females are larger than males, a common trend in spiders, with body sizes of up to 1 inch and leg spans of 3-4 inches,” says Dr. Morehouse. “Males are smaller, about 1/3 for body size, and with leg spans of 1-1.5 inches.”

Where did Joro spiders come from?

The Joro spider or Trichonephila clavata is a species from East Asia, including Japan, China, Korea, Taiwan. According to Dr. Morehouse these spiders were first discovered here in the United States in 2013 in Georgia. They were also spotted in Western South Carolina. “It’s likely that they will continue to slowly expand their range in the warm southern states in the coming years,” says Dr. Morehouse.

Where are Joro spiders?

In the United States they have been discovered in the southeast. “This is not a surprise because the indigenous species Trichonephila (known as the golden silk spider or banana spider) is also found there and they have similar habitat requirements,” explains Professor Anne Danielson-Francois.

Is it true that spiders, like the Joro spider is helpful for the planet?

Yes! These spiders are helpful to humans. “Web-building spiders, like the jojo spider, capture a lot of insects including mosquitoes and other flies, which can be considered pests,” explains Dr. Shahan Derkarabetian. “In a sense, having spiders around actually does humans a favor. That said, invasive or introduced species like the Joro spider may have detrimental effects on native spider species, like outcompeting them for food.”

How can you get rid of Joro spiders?

Don’t call your pest control specialist! Focus on co-existing with these harmless creatures. “They provide free pest control by eating large flying insects such as praying mantis, brown marmorated stink bug, and others,” advises Professor Anne Danielson-Francois. “The golden silk of their web is exquisite and silk from members of the genus have been used to create tapestries.” Check this out!

If you really want them to get off your land Dr. Morehouse suggests that you capture the spider in a glass canning jar and transport it off your property. “Using pesticides risks killing other beneficial insects or spiders on your property, and more creative eradication methods like using torches or other flaming devices literally backfire on homeowners every year,” says Dr. Morehouse. “But my best advice is to adopt a stance of curiosity toward these newcomers, which live fascinating and surprisingly beautiful lives, all while eating lots of insects every day and night.”

Next, How Do Spiders Build Webs?