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For residents of the southeastern United States, fall signals the return of Joro spiders—huge, bright yellow arachnids from Asia—haunting porches, gardens, and just about anywhere big enough for casting enormous webs.
Joros don’t typically pose serious threats to humans. But their autumnal abundance does appear to be the source of significant irritation for local residents—something that David Coyle, an entomologist at Clemson University, knows better than most, as South Carolina’s state advisor for invasive species.
After years of fielding Joro-related complaints, Coyle and his team decided to officially investigate these inquiries—a years-long effort resulting in two studies addressing the most common questions about Joro spiders, published Wednesday, October 22, in the Journal of Medical Entomology and the Journal of Economic Entomology.
Gizmodo spoke with Coyle about the spiders and shared tips for dealing with unwanted Joro encounters. The following conversation has been lightly edited for grammar and clarity.
Gayoung Lee, Gizmodo: What are Joro spiders, and why are they considered invasive?
David Coyle: Joro spiders are native to China and parts of Asia. They first got to the U.S. probably around 2010 but were first discovered in 2014 in northern Georgia. Since then, they’ve spread to multiple states, even all the way up into the Northeast. There are populations in and around Baltimore, Boston, and Pennsylvania. The hotspots are definitely northern Georgia, western South Carolina and North Carolina, and far eastern Tennessee.
They are an invasive species because… well, they’re not native to this continent, and they show pretty significant displacement of native species. This is the fifth year of our “spider surveys,” as we call them.
And, where you have high populations of Joro spiders, you have little to no native or weaving spiders of that type. It’s still too early to know what their true impact will be, but we’re trying to track that down.
Gizmodo: Why do people consider Joros pests?
Coyle: They’re incredibly pestiferous, in that they are very comfortable being in and around human structures and landscapes. They won’t go inside a house at all, but they’ll be on your bushes, on the carport, on the deck, and across doorways. They’re also very big and yellow, so people notice them, and we get lots of calls about these things every fall.
Gizmodo: What kind of calls?
Coyle: Broadly speaking, “How do I get rid of them?” Whether that’s “on my favorite bush outside” or “they put a web across the pillars to my house.” The second most common question is, “Are they dangerous? Will they bite me? Will they bite my kids? Will they bite our pets?”
Because these webs are huge—they can be 10, 15, or 20 feet across—and you walk into them to find a big spider on your head. When the adult females, these great big yellow-and-gray striped females, appear all over the place, people think, “Holy crap, what is going on out there?”
Gizmodo: And what advice are you giving the callers?
Coyle: This was actually the reason we did the new studies. We wanted to get concrete answers that weren’t just anecdotal. Based on the cumulative years of our team’s experience, we knew what happened here. We needed to do it in a scientific way to prove it.
Gizmodo: I see. And how did you answer these questions in the paper?
Coyle: I’ll start with what we call the management study, the one for the Journal of Economic Entomology. That was in response to the question, “How can I get rid of them?” So we looked online because we figured this was where people go to find solutions.
We knew there were legitimate spider control products, so we tested several of those. Then we also evaluated things that we just found online: bleach, machine lubricant, hairspray, and some of these non-pest products that people used.
In a scientifically legitimate and systematic way, we tested every one of these compounds on a bunch of spiders to see if it would kill them, and if so, how long it would take. If not, will it at least make the spider leave? Because for some people, maybe they just want it off their porch—not necessarily dead.
What we ended up finding was that most of the commercial products work great. I’m not going to list any specific brands, but if it’s labeled as a spider control, that stuff works pretty darn good.
Other things worked, too. I mean, machine lubricant works, but we do not advocate spraying that stuff all over your yard. That’s not what it’s for. We strongly recommend just using the stuff that’s labeled for that purpose, because it works just as well.
Gizmodo: The second paper is about whether Joros are dangerous, right?
Coyle: Right. We did a series of tests where we looked at a spider’s reaction to, basically, the human hand. We walked up to spiders in webs. We did everything from just holding our hand near it, trying to touch it, holding it in our hands, cupping it inside, to giving it a little squeeze.
And in almost every case, that spider just wants to get away. They don’t want to be held. They don’t want to be touched. If you cup them in your hands, they just sort of sit there and freeze. The only time you can really get them to bite is when you pinch them—like, really aggravating it.
Then we said, “Okay, let’s say that someone does get bit. How bad is it?” We got 22 volunteers and had them get bitten by Joros. Then we tracked the bite over the course of a week and had the volunteers rate the level of pain based on a system used by pediatricians.
What we found was that it was akin to a mosquito bite. So it’ll be a little swollen, red, and itchy for about 24 hours, then it pretty much goes away. And most of the pain levels were super low, like 1 to 2 out of 10.
So the take-home message is that, if you’re going to get bit by a Joro spider, you’ve pretty much got to be really antagonizing the spider.
Gizmodo: You probably brought it upon yourself.
Coyle: You 100% brought it upon yourself. Like, they want no part of you. They would rather not be on you. They would rather not be held by you. They just want to do their thing and be left alone.
And if you accidentally walk into them, what’s their response? They’re going to drop to the ground and try to get away from you and get off it.
Gizmodo: Having said all that, do you have any personal advice for coexisting with Joro spiders?
Coyle: You don’t have to use chemicals to get rid of these things. A broom works great, your foot works great, and a stick works great. And if you just knock them out of their web a few days in a row, they’re going to take off and go somewhere else. I always tell people that using chemicals for something like this is often overkill, figuratively speaking.
Then the other thing is that I’d reinforce that they’re not going to come in your house. They don’t want to be in your house. This type of spider in general puts its webs between big things outside so stuff can fly into it. So, if there’s a Joro spider in your house, that means somebody brought it in there. It’s plain and simple.
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Gayoung Lee
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