We don’t often do content warnings on these blogs but: this one is about spiders, there are photos and discussion of spiders, and readers who don’t like spiders may want to keep that in mind.
Spiders are a presence in most gardens, and in many ways they’re a good sign that a garden is a health and living space. Spiders prey on a variety of insects, many of which are unwanted garden pest, and they play a critical role in both the ecosystem and the health of our plants. And just as some plants are introduced or invasive species, some insects and arachnids are too. Over the last 15 years, the Joro spider has become an increasingly common invasive in the southeastern USA, and is expanding up the eastern coast of the country. Those of us with outdoor garden spaces may have already seen them—so what do we do about them. In this blog we’ll take a look at the Joro spider, learn a bit about it and how to identify it, and explore its impact on our garden spaces.
Let’s dig in!
Gardzen Executive Summary
· Joro spiders, or Trichonephila clavata, are an invasive species in the North America
· Originally from East Asia, Joro spiders likely arrived in the southeastern US in the early 2010s
· Since then, the Joro spider has spread across the Southeast and may spread further
· Joro spiders are largely harmless, though research as to their environmental impact is ongoing
· Gardeners can do a lot to help scientists and government agencies track the spread fo the Joro spider by reporting sightings to state cooperative extensions
Where did Joro Spiders Come From?
Most properly know as Trichonephila clavata, the Joro spider is a native of East Asia, found throughout eastern and southern China including Taiwan, most of Japan, and Korea. The name “Joro” comes from the Japanese Jorō-gumo or “ジョロウグモ” in Japanese kana script.
Like all members of the Trichonephila genus, the Joro spider is a golden orb weaver and is thus related to the other orb weavers that are found throughout the US. “Orb” describes the circular patterns this particular genus often uses in weaving its webs, but here the Joro spider is unique. Instead of a regular orb pattern, it uses a three-layered approach with a a central orb with irregular patterns in layers both in front of and behind it. This is a relatively easy way to identify a Joro spider and its web.
The spiders themselves have a typical orb weaver body with long legs and a large yellow and dark blue striped abdomen. Mature females have a red spot or blotch towards the rear underside of the abdomen. The females can be especially large—up to 1 inch/25mm in in body length not counting the legs. The males are around .3-.4 of an inch/7-10 millimeters in body length, again not counting the legs.
How did Joro Spiders come to North America?
As far as we can tell, Joro spiders arrived in the US via cargo shipments, mostly like traveling via ships to ports in the Southeast. They were first identified in the USA in the early 2010s, mostly in South Carolina and Georgia. Since then, they’ve spread to North Carolina, Tennessee, and maybe further up the east coast and into the South. As a relatively cold-tolerant species Trichonephila clavata can inhabit a variety of climate zones. However, their population center still seems to be Atlanta, Georgia, and it’s likely that’s where they first arrived.
Are Joro Spiders Dangerous?
The short answer is: no, Joro spiders are not especially venomous or dangerous to humans in any direct way. A bit does contain some venom, but in most people the worst response is an allergic reaction or some itching. Obviously we should seek medical attention if any insect bite gets worse than itching or a mild allergic reaction, but Joro spiders aren’t of any great concern to humans or pets.
They’re also shy—these spiders try to avoid contact with humans or larger animals and generally build their webs away from regularly trafficked areas in gardens. The can and will build webs anywhere, however, so don’t panic if you see them in other places.
Unlike many invasives, there’s a chance that Joro spiders may have a positive environmental side effect. Joro spiders do compete with native spiders and birds for space and food—insects, of course—but Joro spiders also feast on the invasive marmorated stink bug. The sting bug is a common garden pest that causes big problems for food plants and commercial agriculture, and the Joro spider may help us by reducing those populations to a useful degree.
The truth however is that we don’t know what kind of impact the Joro spider will have; it’s a new arrival in the US and its impact is still being studied. If you see one in your garden, you may way to report it to your state cooperative extension and let them know so they can track its spread.
Why Gardeners are Important for Environmental Issues
Gardeners were among the first to notice the Joro spider when it arrived in Georgia, and reports from gardeners have been instrumental in tracking the spread of this species. The impact that Trichonephila clavata will have on the overall environment in its new home remains to be seen, but we do know that gardeners play an important role in understanding how it got here, how it spread, and how Joro spiders are interacting with their new home. For us this is a reminder that gardening is a community and that gardeners are an important reminder that humans and nature are all part of the same natural system.
Have you seen a Joro spider? Do you have cool photos of spiders in your garden space? Indoors or out we’d love to see them so please send them via email!
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