Despite what you may have heard, the Jorō spider is docile and poses no known threat to humans or pets. Image credit: David Coyle
Last week a team of scientists from Southern Adventist University, University of Florida Lake Alfred, University of Texas El Paso, Clemson University, and an unaffiliated researcher really captured the interest of the media with predictions that a large orb-weaving spider, the Jorō spider, was poised to expand its range from its southern stronghold to states further north. Jorō is native to eastern Asia, Japan, China, Korea, and Taiwan. Although it likely arrived in Georgia around 2010 it is now found in Florida, Alabama, Mississippi, the Carolinas, Tennessee, Kentucky, Virginia, West Virginia, Maryland and Ohio. Jorō joins its cousin the golden silk spider, Trichonephila clavipes, as a spider from afar that has established residence in our land.
The underside of the Jorō spider has striking red markings. Image credit: Bob Bellinger
The golden silk spider has been in the US for more than a century, where it occupies parts of Florida, several other southeastern states, and even rarely makes an appearance elsewhere, sometimes as far north as Pennsylvania. The golden silk spider, a native of Central and South America, has remained mostly bottled up in the south likely due to its inability to tolerate cooler temperatures further north. However, a recent study by Dr. Nelsen and colleagues found evidence for abundant suitable habitats in eastern North America and some in western North America that could support the Jorō spider. In southern states, populations of the Jorō expand rapidly once they become established in an area. Jorō also has remarkable talents when it comes to moving great distances. In nature, the typical mode of dispersal of many spiders, including Jorō, is by aerial dispersal of spiderlings. They balloon on strands of silk like Charlotte's babies in the book of the same name. By the way, ballooning likely has given rise to the more spectacular moniker for Jorō, the “parachute spider." No, they really will not rain down on you from airplanes. Long distance transit by Jorō probably depends on human assistance, as both adults and their spawn are good hitchhikers. Jorō may have entered this country as an inseminated and gravid female or as an egg-case stowaway in a cargo container from Asia. Rapid population growth coupled with its ability to be transported inadvertently by humans and naturally by ballooning make range expansion likely. Previous research by scientists Davis and Frick found that Jorō spiders have a higher metabolism, supported by a faster heart rate, and a better ability to tolerate freezing temperatures than their warmth-loving cousin the golden silk spider. These traits, combined with more rapid development, enable Jorō to complete its life cycle rapidly before chilly temperatures bring its seasonal development to an end. This suite of adaptations may enable Jorō to escape the relative warmth of the south and expand its range northward along the eastern seaboard.
The bite of the “venomous” Jorō will be terrible and painful, right? Nah, according to expert Rick Hoebeke, the risks to humans and pets are small due to the puny size of Jorō’s fangs, which are unlikely to pierce our skin. I have visited Jorō’s cousin, the golden silk spider up close and personal in the rainforest of Costa Rica and found the large females to be completely non-aggressive. These spiders are passive hunters that build enormous webs, larger than a meter in diameter, to capture prey snared by silk. For arachnophobes these may be scary, but for arachnophiles these are beautiful spiders which may provide important ecosystem services including biological control of crop pests such as brown marmorated stink bugs or spotted lanternflies, with which they have an ancient association in their native range in Asia. Jorō spiders may be like Hannibal Lecter "having an old friend over for dinner" when they reunite with the stink bug or lanternfly here in the US. Large spiders like these may also become juicy prey items for feathered and non-feathered reptiles.
The large and beautiful Jorō spider poses no known direct threat to humans or pets. Like its cousin from Central and South America, the golden silk, Jorō is here to stay in the United States. Jorō often becomes the dominant orb weaver in colonized locations. Here is the mystery. How will Jorō affect indigenous orb weevers like the pretty marbled orb weaver, spotted orb weaver, and my favorite, the black and yellow garden spider, destroyer of stink bugs? If you spot Jorō in your neighborhood, please report it to iNaturalist.
As with all non-native species that arrive on our shores, it is difficult to predict what impact they will have on our ecosystems but experts suggest that beyond their somewhat scary mien, and maybe giving our indigenous large orb weavers like the black and yellow garden spider, marbled orb weaver, and spotted orb weaver a run for their money. In locations in other parts of the world where Jorō is established, it often becomes the most abundant and dominant orb weaver. What will it mean for our resident spiders and their ecosystems? Only time will tell.
In 2022 when Bug of the Week first talked about the Jorō spider, its presence in the DMV was speculative. But in 2023, several sightings of the Jorō spider were confirmed by iNaturalist in Howard County Maryland. The fascinating part of this story stems from the fact that images clearly show both male and female Jorōs present in the landscape. How did they arrive in Maryland hundreds of miles distant from their southern redoubts? While ballooning is possible, the likelihood of both male and female spiderlings dropping from the sky into the same location and hooking up seems somewhat unlikely. Perhaps a gravid female spider or an egg case hitched a ride from down south and inadvertently arrived in eastern Howard County. The million-dollar questions are, of course, did the Jorō survive the mild winter of 2023-2024 in Maryland and will we see even more of this gorgeous spider this year? Clearly, a road trip to eastern Howard County is in order for the Bug Guy. One final tidbit about Jorō comes from Japanese folklore. Jorō is a shapeshifter known as Jorō-gumo. Jorō-gumo turns into a beautiful woman, seduces men, binds them with silk, and devours them. Yikes! Sounds like a bad date to me.
Acknowledgements
Bug of the Week thanks Rick Hoebeke for identifying Jorō as it arrived in the US and for providing insights into the ways of these large beautiful spiders. We also thank David Coyle and Bob Bellinger for sharing great images and knowledge of Jorō. Fascinating studies entitled “Veni, vidi, vici? Future spread and ecological impacts of a rapidly expanding invasive predator population by David R. Nelsen, Aaron G. Corbit, Angela Chuang, John F. Deitsch, Michael I. Sitvarin and David R. Coyle, “Physiological evaluation of newly invasive Jorō spiders (Trichonephila clavata) in the southeastern USA compared to their naturalized cousin, Trichonephila clavipes” by Andrew K. Davis and Benjamin L. Frick, “Nephila clavata L Koch, the Joro Spider of East Asia, newly recorded from North America (Araneae: Nephilidae)” by E. Richard Hoebeke, Wesley Huffmaster, and Byron J Freeman, and “The Life Cycle, Habitat and Variation in Selected Web Parameters in the Spider, Nephila clavipes Koch (Araneidae)” by Clovis W. Moore ND provided the inspiration for this story and details surrounding the stars of this episode.
To see other large orb weavers and differentiate them from the Jorō spider, please click on this link: https://resources.ipmcenters.org/view/resource.cfm?rid=27877
To hear more about the Jorō spider and calm your fears about Jorō, please click on this link to watch Jorō guru David Coyle’s take on this spider: https://youtu.be/zhO_bwwg-E4?si=nhd9au-t-HRCmw6b