The Joro spider, a sizable and visually distinct arachnid, has become increasingly noticeable across parts of the United States. Its widespread presence has prompted questions about its potential impact on local environments and whether intervention is necessary.
Meet the Joro Spider
The Joro spider, scientifically known as Trichonephila clavata, is an orb-weaver species originally from East Asia, including Japan, Korea, China, and Taiwan. These spiders are believed to have arrived in the U.S. around 2013 or 2014, likely as stowaways on international shipping containers, first being detected in Georgia. Adult female Joro spiders are striking, exhibiting vibrant yellow and black coloration with blue bands on their legs and distinct red, yellow, and black patterns on their abdomen. They are considerably larger than males, with a leg span that can reach up to four inches, roughly the size of a human hand.
Joro spiders construct large, golden, wheel-shaped webs that can span up to 10 feet in diameter. These webs are often found stretched between trees, shrubs, and man-made structures like porch lights or power lines. While adults do not fly, young spiderlings use “ballooning,” releasing silk threads to catch the wind and travel to new locations.
Assessing the Threat
A common concern revolves around the Joro spider’s potential danger to humans and pets. Like most spiders, Joro spiders possess venom, which they use to subdue their prey. However, their venom is not considered medically significant to humans, with bites typically resulting in mild symptoms comparable to a bee sting or mosquito bite. Any resulting irritation, such as redness or swelling, usually subsides quickly.
Joro spiders are generally docile and non-aggressive. They tend to avoid confrontation and will only bite if directly provoked or trapped, such as being pressed against skin. Their fangs are often too small or weak to effectively puncture human skin, making bites uncommon. These spiders prefer to conserve their venom, using it only as a last defense.
Ecological Impact
Joro spiders are generalist predators, consuming a wide array of insects that become entangled in their large, sticky webs. Their diet includes various common insects, such as flies, mosquitoes, and even brown marmorated stink bugs, which are themselves an invasive species that can damage plants. This dietary preference suggests they may contribute to the control of certain insect populations.
Initial concerns arose regarding whether Joro spiders might outcompete native species for food or habitat. While some research indicates a potential decline in native orb-weaver populations in areas with high Joro spider abundance, their overall long-term impact on native ecosystems is still under study. Many experts suggest Joro spiders do not significantly displace native arachnids or cause widespread ecological disruption. They may even serve as an additional food source for native predators like birds.
Expert Advice and Action
Given the Joro spider’s characteristics, entomologists advise against killing them. Joro spiders are largely harmless to humans and pets, and their presence is becoming a natural part of the ecosystem where they have established themselves. Attempting widespread extermination is impractical and ineffective for population control due to their rapid spread via ballooning and adaptability.
Instead of killing Joro spiders, practical advice for individuals encountering them involves leaving them undisturbed, especially in less-trafficked areas of a yard or garden. If a Joro spider or its web is in an inconvenient location, such as a doorway or walkway, gentle relocation is an option. This can involve using a stick or broom to carefully move the spider and its web to a more suitable spot a reasonable distance away. Destroying webs in high-traffic areas can also encourage them to rebuild elsewhere.