What looks like something out of a nightmare scene is starting to turn up across Southern California: large, brightly patterned spiders with long legs that can span roughly the width of a human hand.
The species behind these sightings is the invasive Joro spider, an orb-weaving spider native to East Asia that has been gradually spreading in the United States.
Reports suggest this species is no longer confined to its earliest known American foothold in Georgia, where it was first documented in 2013. Scientists believe the spiders likely arrived in the country hidden inside international shipping containers before beginning their slow expansion across states.
The adult females are especially striking and hard to overlook. They can grow to about 1.25 inches in body length and display vivid coloring: yellow bodies accented with blue-green markings along the back, with hints of red and yellow on the underside. Their long legs are mostly black but marked with bold yellow bands. Males, by contrast, are much smaller at roughly a quarter-inch, with slimmer brown bodies and subtle yellow striping and a darker central line, making them far less noticeable.
These spiders don’t just spread by walking. When they are young, they use a method called “ballooning,” releasing strands of silk that catch the wind and carry them through the air like drifting parachutes. While they cannot truly fly, this technique allows them to travel significant distances, and recent sightings have placed them as far as Santa Barbara County.
Their reproduction is another factor that helps them spread quickly. From mid-October through November, females produce egg sacs that can contain between 400 and 500 eggs. These thick, white silk sacs can attach to almost any surface, including tree bark, leaves, and even man-made structures like buildings, allowing them to appear in a wide variety of locations.
Despite their intimidating appearance, experts emphasize they are not considered dangerous to people. Pat Wooden, who manages an insect identification lab at Virginia Tech, has noted that they are not harmful in terms of biting or causing serious injury. Their fangs are too small to break human skin, and they tend to be extremely non-aggressive, often remaining still or “playing dead” for extended periods when disturbed.
Their webs can grow quite large—sometimes reaching up to 10 feet across—and they are effective hunters of insects many people find irritating, including mosquitoes, flies, and even the invasive brown marmorated stink bug.
Still, for residents used to sunny skies and palm trees, encountering a large yellow-and-black spider suspended in a wide golden web can be an unsettling sight.