Invasive Joro Spiders Detected in Southern California After Initial US Arrival in 2013

The Joro spider, scientifically named Trichonephila clavata, is an invasive species originating from East Asia. It was first observed in the United States in Georgia in 2013. Recent sightings indicate its presence in Southern California, including Santa Barbara County.

25 inches in body length, with legs spanning the width of a human hand. Their bodies feature yellow coloring with blue-green streaks on the back and red and yellow markings underneath. The legs are black with yellow bands.

25 inches in length. They have brown bodies with faint yellowish stripes and a darker line down the center. Their appearance is less vivid compared to females.

Spread and Reproduction Joro spiders likely arrived in the US via shipping containers.

As spiderlings, they employ ballooning, releasing silk threads to drift on the wind over distances. This method allows them to disperse widely. Females produce egg sacs containing 400 to 500 eggs between mid-October and November.

These sacs, constructed from white silk, attach to surfaces such as leaves, tree bark, or buildings. The sacs enable the spiders to establish in new areas.

Behavior and Ecological Role Joro spiders construct webs up to 10 feet in diameter.

Their fangs are too small to penetrate human skin, and they avoid confrontation by remaining motionless when threatened. These spiders feed on insects including mosquitoes, flies, and the invasive brown marmorated stink bug. While they do not harm humans or cause structural damage, their appearance may concern residents in affected regions.

The spread of Joro spiders highlights ongoing challenges with invasive species in the US. Monitoring efforts continue in areas like Southern California to track their distribution. Further observations will determine their long-term establishment.