The Joro spider (Trichonephila clavata) is native to East Asia and was first detected in Georgia in 2014. It has been found in Georgia, North Carolina, South Carolina, and Tennessee, and is spreading to adjacent regions. It has one generation per year in its native range.
Life cycle
Egg sacs are laid from mid-October to November and are dense, white silk sacs containing 400 to 500 eggs. These sacs are attached to leaves, tree bark, and human-made structures.
Adult females become sexually mature in September and early October. The female body is about 0.67 to 1.2 inches long and bright yellow with broad, horizontal bluish-green bands on the top side of the abdomen and large red markings on the underside of the abdomen. She also has long black legs with yellow-orange bands or, more rarely, all-black legs.
Adult males mature by late August. The male body is about 0.16 to 0.31 inches long. The cephalothorax is light brown with two dark brown long bands on both sides. The abdomen is elongate-oval with a greenish-brown topside that has two yellowish long stripes on both sides of a dark brown middle line.
Joros and similar native spiders
The closest look-alike in the southeastern United States is the golden silk orb weaver (Trichonephila clavipes). The adult female golden silk orb weaver has rows of silvery white spots on its abdomen instead of blue bands, and her legs are yellow-orange with brown bands. Three of the four pairs of legs have black tufts of hair at the joints.
Photo: Whitney Cranshaw, CSU, Bugwood.org
Photo: Chris Evans, University of Illinois, Bugwood.org
Photo: Leslie J. Mehrhoff, UCon, Bugwood.org
Basic spider biology
Joro spiders are in the golden orb weaver genus, Trichonephila, a diverse group commonly occurring in tropical, subtropical, or temperate areas. Similar to other golden orb weavers, adult females have distinctive coloration, but juvenile spiders may have varying color patterns. These spiders also show sexual dimorphism, meaning that sexually reproductive males and females look different from each other. With Joro spiders, females can be as much as 500 times heavier than males. If you look closely at a female’s web, you may find one or more males inhabiting it.
An interesting characteristic of adult Joro webs is their golden color, which is why they are considered golden orb weavers. Researchers speculate that the golden pigment may deter vertebrates such as birds from damaging the webs, or it may attract insects. The spiders’ silk glands produce the silk threads using a variety of proteins and also produce sticky glue-like drops for prey capture. Silk threads are elastic and very strong, and different silk types serve different purposes. Dragline silk helps spiders anchor themselves and their webs, while the silk used to capture prey in web spirals is highly flexible.
Silk also helps spiders spread over long distances through ballooning. Spiders release silk strands that catch wind currents and can carry them many miles. Ballooning is common in many spider species, especially when spiders are smaller and lighter juveniles.
Where Joro spiders have been found
An EDDMapS distribution map of confirmed counties as of March 2022 showed the species established in multiple southeastern states. A single Joro spider was also observed and reported in Washington County, Oklahoma, in November 2021. Based on available data, the spiders appear to make webs on many surface types and commonly along habitat edges, such as the perimeter of a park or yard, as well as between powerlines. View the most current map on the EDDMapS site: www.eddmaps.org/distribution/uscounty.cfm?sub=87670&map=density
When the spiders appear
Small juveniles begin showing up as early as May, but they are not easily detectable and often look like other spiders. Based on public observations and reporting, more mature spiders are typically observed in late July and August, with peaks in September and October.
Potential ecosystem effects and management
Whether Joro spiders are disrupting ecosystems or displacing native species is still unknown. Researchers are actively studying this question, and public reporting helps them understand where the spiders are occurring. Observations can be submitted through the Joro Watch website or the EDDMapS app, ideally with counts and photographs.
Some homeowners view Joro spiders as a nuisance, which is common for many spiders. Spiders’ roles often are underappreciated, but they are important insect predators and globally consume an estimated 400 to 800 million tons of insects. If spiders are bothersome in a pathway or certain parts of a yard, they can be removed with a long stick or pole. Guidance videos on the Joro Watch website explain how to wrap the web around the spider using a broom, telescoping paint pole, PVC pipe, or similar tool and then remove it from the pathway.
Until more is known, broad use of insecticides is not advised. The available insecticides for spiders are broad spectrum, meaning they kill many kinds of insects and spiders. Beneficial insects, such as pollinators and predators that help suppress pests, may also be killed. When these natural enemies are removed, pests such as aphids, scales, mealybugs, and mites can become bigger problems in yards, parks, natural areas, and agricultural or horticultural settings.
