Updated September 19, 2025 01:36PM
With a leg span of up to four inches and webs that can span 10 feet, Joro spiders (Trichonephila clavata) are big, attention-getting arachnids with a habit of building their homes on garages, trailside shelters, and other human buildings. And they’re some of the Appalachian Trail’s newest denizens: While Joros have been in the United States since about 2013, when scientists believe the east Asian species arrived on a cargo ship, they’ve expanded their range into the Appalachian Trail corridor in recent years. In 2024, the spiders made their first confirmed appearance in Great Smoky Mountains National Park. Now, the NPS is asking hikers to help them track Joro sightings as the spiders continue to spread.
To learn more, I sat down with Dr. Francisco Garcia Bulle, director of research and conservation at Westminster, Colorado’s Butterfly Pavilion, for a mythbusting conversation about the most hyped arachnids of the 2020s. Can Joro spiders bite? Can they really fly? And what should AT hikers do if they see one? Check out our discussion and learn the answers to these questions and more.
Adam Roy: I’m Adam Roy, editor-in-chief of Backpacker. Last year, for the first time, the National Park Service announced it had found a Joro spider, a large invasive species of spider from East Asia, within the boundaries of Great Smoky Mountains National Park. Now the agency is asking hikers to help it track this new species as it spreads through America’s most popular national park. Joining me is Francisco Garcia Bulle, the director of research and conservation for Butterfly Pavilion in Westminster, Colorado. Francisco, thank you so much for being here. Can you tell me a little bit about Joro spiders and why they’re getting so much attention right now?
Francisco Garcia Bulle: Yeah, of course. Joro spiders are spiders that come from Asia, so they’re coming from Japan, China, Korea, Taiwan, and they have been introduced in the US, most probably accidentally, they came in a shipping container. And the first time they saw them here was between 2013 or 2014 in Georgia, and since then they have been spreading and just reproducing and these populations have been growing over the years.
Adam: These spiders are pretty big. That’s a notable thing about them. The females can have leg spans of, I think, about up to four inches, which makes them one of the largest spiders in the United States. Are they dangerous to people or pets? Should hikers be worried about them?
Francisco: They’re not dangerous at all, and we would like to scale back that in there and just understand that invertebrates [don’t always have] the best fame. Here at Butterfly Pavilion, we really try to just give them that voice and understand that most of them are not a threat to humans. They’re actually playing really important roles out there in nature, such as pest control or decomposition or pollination. So in the case of spiders, spiders have this fame where they can be creepy or they can be scary. They’re actually super important for ecosystems out there, and Joro spiders, even though they’re big, they’re actually quite harmless. They are venomous, but if you get bitten, it’s just going to be like a mild bee sting, so it’s not going to be a big problem, and they’re actually going to be very shy. So if you approach them, they might probably just go and hide in their web.
Adam: So if I find one of these spiders weaving its gigantic web across an Appalachian Trail shelter, I shouldn’t be worried?
Francisco: You shouldn’t be worried. They’re not dangerous at all. They’re super harmless and they’re actually really beautiful to look at. We really encourage people to actually have this curiosity and go look at them.
Adam: So do you want to tell me a little bit about why they’ve been so successful at spreading through the eastern seaboard?
Francisco: Yeah, so there’s this myth going on that these spiders can fly, right? People think they have wings or they’re just flying all around.
Adam: Oh, you’re telling me they don’t?
Francisco: They don’t have wings. Spiders do not have wings. Some spiders, what they will do is when they are spiderlings, which is like a baby spider, they will spin this little web in the shape of a parachute. And they will just put that out there and then with some wind they will start spreading and they will move there, and that’s how they can spread and move around. So the spiderlings are just opening their little parachutes and going all around the environment, which is super interesting.
Adam: So we know these spiders are not dangerous to people, but I’ve seen some research suggesting that they could have a negative impact on the environment. Can you tell me a little bit about what we know and don’t know about that?
Francisco: Yeah, of course. So these spiders are not a native species here. Any species that has been introduced might have a negative impact in the environment. In the case of these spiders, one of the impacts that might be seen is changing these food chains, so they might be eating a lot of pollinators that are very important out there or very rare pollinator species of concern. They are not being picky about their food. They’re just going to take whatever they can from their food web, right? And the other thing is, they might be outcompeting other orb-weaver spiders that might be native.
So these are great questions, because then they just show us how understudied invertebrates are. We don’t know much about them. We need to start getting more funding to do more research into invertebrates, and at Butterfly Pavilion we’re doing that, right? We’re trying to really understand more about them and just really do more projects around their conservation or the effects they may have out there in the environment, so that’s really important.
On the silver lining of things, these spiders are adapting really well to the cities, and they are great pest controllers, so cities might have some problems with mosquitoes or flies or cockroaches, so they are eating these animals too. So that’s a little silver lining.
The easy answer is we don’t know what the effects might be. We need to wait. They were introduced, as we said, not that long ago, so we’re still doing those studies to understand what the actual effect is gonna be.
Adam: You talked a little bit about research. The National Park Service is asking hikers to help with this research project on Joro spiders now by logging their sightings within Great Smoky Mountains National Park. Can you explain how they should be doing that and why that information matters?
Francisco: It matters a lot because working with inverts, as we said, it’s hard. They’re very small. They can move very fast, so understanding how these movements are happening is crucial, but with one single person it’s really hard. You need a lot of people doing this, you need a big community. One of the best ways they can do it, it’s pretty simple, is downloading an app that is called iNaturalist, and within this app they can take pictures of the animals. They can upload them on the place they saw them, and that way that allows other biologists to be able to recognize these species and be able to track down where they are seeing them. And that way it helps us a lot to understand every year where these spiders are moving and what’s their new frontier or limit that is happening.
Adam: You don’t have Joro spiders here at Butterfly Pavilion, but you do have a very closely related species of spider. Every year, if I remember correctly, you turn part of this butterfly garden here into a spider zone for Halloween. You bring out a bunch of different orb-weavers and let people wander among them. Do you want to tell me about the species you have here that’s most like Joro spiders?
Francisco: Yes, so we have orb-weavers and it’s the golden silk orb-weaver. [Editor’s Note: Trichonephila clavipes, commonly known as the gold silk orb-weaver, is a web-weaving species of spider native to the United States that’s closely related to Joro spiders.] We’re going to have hundreds of them, which is super exciting. We want to celebrate them.
So starting on the last day of September and going all throughout October, we’re going to have Spiders Around the World, which is an exhibit just celebrating all spiders, and all our exhibits are gonna be around spiders. We’re going have all these different tarantulas and spiders on display. And within our butterfly conservatory, we’re going to have a space only dedicated for free-roaming golden orb-weaving spiders, which is super exciting. They can experience some of their closest relatives up close and see how harmless they are and how cool they are.
Adam: So if AT hikers want to get a little bit of exposure therapy, you’re telling me they can come here in October?
Francisco: It’s an exposure therapy, but it’s really shifting that perspective to be like, OK, they’re not aggressive animals, they’re not dangerous animals, they’re really cool. They’re here playing this role of controlling pests and really minding their own business. And they’re also really beautiful. I want to say, I don’t know if I’m a little bit biased, but they’re really cool. So it’s really cool to just show it to your kids or your friends or your family members and really talk about how cool spiders can be and all the important roles they are playing out there in nature.
Adam: Francisco, thank you so much for taking the time to enlighten us here. If you want to learn more about Joro spiders and animals you might encounter on the trail, go to www.backpacker.com. Until next time, I’m Adam Roy.
