The Joro spider, Trichonephila clavata, has recently captured public attention due to its noticeable presence and distinctive appearance in new regions. This article aims to provide clear overall information about these arachnids, addressing common questions about their identification, origin, behavior, and potential impact.
How to Identify Joro Spiders
Joro spiders are large, visually striking orb weavers, making them relatively easy to identify. Adult female Joro spiders are particularly noticeable, with bodies growing up to 1 inch long and leg spans reaching up to 4 inches, roughly the size of a human palm. Their abdomen features bright yellow and black stripes, with some also displaying blue-black and red markings on their underside. Their long, black legs often have distinct yellow bands.
Male Joro spiders are significantly smaller and less colorful, typically measuring around 0.3 inches in body length and appearing drab brown with darker stripes. Immature females initially have a blotchy black and yellow pattern that develops into distinct bands as they mature.
Where Joro Spiders Come From
Joro spiders are native to East Asia, including Japan, China, Korea, Taiwan, and Vietnam. They are believed to have arrived in the United States around 2013 or 2014, likely as stowaways on international shipping containers, with the first confirmed sighting in Hoschton, Georgia. This mode of transport is common for invasive species.
Since their initial detection, Joro spiders have spread across various southeastern states, including Georgia, South Carolina, North Carolina, and Tennessee. Reports also exist in other states like Alabama, Maryland, Oklahoma, and West Virginia. Their ability to tolerate colder temperatures, similar to those in their native Japan, suggests potential for further expansion across the Eastern Seaboard of the U.S. Young Joro spiders can also disperse through “ballooning,” releasing silk strands to catch the wind and travel to new locations.
Joro Spider Behavior and Diet
Joro spiders construct large, intricate orb webs, often golden-tinted, that can span up to 10 feet wide. These webs are typically found between 3 to 9 feet above the ground in open, high-traffic areas like between trees, bushes, or on man-made structures such as porch lights, which attract prey. The silk of their webs is notably strong; studies have shown their webs can support weights greater than an average cardinal.
Joro spiders primarily feed on insects that become entangled in their webs. They subdue prey with venom and wrap it in silk. Their diet includes a variety of flying insects such as mosquitoes, flies, moths, butterflies, beetles, and even larger prey like cicadas and brown marmorated stink bugs. Despite their size, Joro spiders are generally considered docile and tend to remain still in their webs, often freezing for extended periods if disturbed.
Are Joro Spiders a Threat?
Despite their large size and striking appearance, Joro spiders pose very little threat to humans or pets. Like most spiders, they possess venom, which is primarily used to subdue their insect prey and is not considered medically significant to humans. Their fangs are often too small or not strong enough to easily pierce human skin.
Bites from Joro spiders are rare and typically only occur if the spider feels directly threatened or is provoked, such as being squeezed or stepped on. If a bite does occur, the sensation is often compared to a bee sting, causing only temporary redness or mild discomfort. Allergic reactions are possible, as with any insect bite, but severe reactions to Joro spider bites have not been reported in humans or animals. From an ecological standpoint, their impact is still being researched, but some entomologists suggest they might help control populations of invasive pests like stink bugs. They are not known to invade homes, preferring to build their large webs outdoors.