A giant but harmless spider could soon hitchhike or parachute into our area, researchers warn.
Joro spiders, an invasive, palm-sized and colorful species, could be spreading across most of the East Coast, according to a University of Georgia study published in March. The researchers found that the arachnids can survive a short freeze, making them more likely to settle in colder climates.
To learn more about these scary-looking but harmless insects, The Morning Call spoke to Marten Edwards, a biology professor at Muhlenberg College.
What are Joro Spiders?
Joro spiders arrived in the United States nearly a decade ago and have spread throughout Georgia and other southeastern states, according to the university’s study.
They’re similar to golden silkworms, which have thrived in the southern United States for about 160 years, Edwards said.
However, unlike golden silk spiders, joro spiders can withstand cooler temperatures, making them more likely to spread along the coast.
What is unique about them?
Their size and color make them stand out, as does the vast webs they weave.
“They’re so recognizable — they’re huge (3 to 4 inches in diameter, including legs) and have a large, bright yellow, blue-black, and red body.” said Edwards. “They also form huge, bright yellow, spherical webs. … The rides are spectacular works of art and engineering.”
Where are you from?
They’re native to Japan and widespread there, Edwards said.
“Importantly, they are found in those parts of Japan where the winters are as cold as we are likely to expect here in Pennsylvania,” said Edwards. “Joro spiders were introduced to Georgia in 2014 and have already expanded their range.”
How do Joro spiders spread?
Like the spotted lanternfly, Joro spiders are adept hitchhikers and likely first came to the country as stowaways on shipping containers, according to the study. They also have a behavior called ballooning, in which the spiders use their silk to carry them to new places in the wind.
“That’s one of the reasons why Joros was able to spread so quickly in the state of Georgia,” according to a study. “When young animals appeared in the spring, they rode with them to a new place. Their offspring did the same the next year.”
What did the study reveal?
The University of Georgia study compared the Joro spider to its close relative, the golden silk spider.
“The Joro spider has about twice the metabolism of its relatives, a 77% faster heart rate, and can survive a brief freeze that kills many of its cousins.” according to the report. “These results mean that the Joro spider’s body functions better in a cold environment than its relative.”
When can we expect them in the Lehigh Valley?
The University of Georgia study predicted the spiders could spread to many eastern states and possibly Pennsylvania. However, there is no time frame when they might appear here.
Are they dangerous?
Joro spiders do not pose any danger to humans.
“They aren’t poisonous to humans, and most bites wouldn’t even break the skin,” said Edwards. “They won’t enter your home, and they won’t pose a threat to gardens or pets. … Just leave the spiders alone and everyone will be fine.”
How could they affect the environment?
So far, they don’t appear to have a major impact on local food webs or ecosystems, according to the university’s study, and they could be an additional food source for native predators like birds.
What should someone do when they see one?
Unlike other invasive species, such as the spotted lanternfly and emerald ash borer, there is no expert recommendation for killing joro spiders. In fact, these arachnids could do more to help than harm.
“There is absolutely no reason anyone should even consider killing her.” said Edwards. “Our best strategy is to just let them do their favorite activity: eating insects. With a bit of luck they will enjoy our spotted lanternflies. They will also enter the food chain and feed the animals right here.”
What else should people know?
While they may look intimidating, the sight of these spiders in the Lehigh Valley should not be cause for concern.
“There are a lot of things to worry about now. Local occurrences of Joro spiders are at the bottom of the list.” said Edwards. “It’s good to know about its potential spread so you know that if you find one in your yard, there’s no need to worry.”