Invasive Joro spiders found near Philadelphia: Experts concerned

Six enormous, brightly colored spiders were spotted near Philadelphia. A local entomologist determined that they represent the invasive Joro species, which originates from East Asia, including Japan, Korea, Taiwan, and China.

Joro spiders were first noticed in the United States around 2010. Their presence has now been observed again, this time in Bucks County, Pennsylvania, about 40 miles from Philadelphia.

As reported on NBC Philadelphia's website, a local entomologist confirmed the presence of this invasive species during a visit, which was followed by analysis and verification by a researcher from the University of Georgia.

By 2022, this spider's habitat area in the U.S. was about 46,000 square miles, including states like Georgia, South Carolina, North Carolina, and Tennessee.

Reports of sightings of this species have also appeared in Alabama, Maryland, Oklahoma, and West Virginia, according to scientists from Clemson University. Studies have shown that Joro spiders are rapidly expanding their range beyond South Carolina. Data suggest that this spider could inhabit most of the eastern United States.

"These things are here to stay," noted David Coyle, a professor at Clemson University. He added, "their comfort area in their native range matches up very well with much of North America."

Joro spiders overwinter as eggs, and the young spiders disperse as small individuals in the spring. As with most spiders, females are significantly larger than males. The body of an adult female reaches a size of 0.7 to 1 inch, while the male measures 0.3 to 0.4 inches.

The females' web can reach several meters in length. In sunlight, the yellow threads look like gold. The structure of the web, viewed in cross-section, is unusual for orb webs, consisting of three layers: a central orb and two irregular layers in front and behind.

Both males and females have large abdomens and long legs. Adult females are colored with yellow and dark blue stripes, and a red hue appears on the back of their abdomen.

In the fall, smaller males can be seen in the webs of females for mating. After reproduction, the female lays a cocoon containing 400 to 1,500 eggs on a tree. Her life cycle ends with her death in late fall or early winter. The new generation hatches in the spring.