Jorō spiders, the mysterious arachnids invading the US, freeze when stressed, study shows

Although the invasion of Jorō spiders is inevitable as they spread across the southeastern United States, scientists continue to learn more about the giant venomous flying arachnids, including how they remain cool under pressure.

Researchers at the University of Georgia (UGA) published a study in the journal Physiological Entomology on Monday detailing how Jorō spiders' heart rate is the best indicator of stress levels.

“They can live in pretty crazy places. I’ve seen them on top of gas station pumps, and there are cars whizzing by left and right every few seconds — that’s a really kind of disturbed, stressful environment for a lot of critters. And so one thought we had going into this was, ‘well, maybe the Jorō spiders just don’t even get stressed,’” lead author of the research Andy Davis, a research scientist at the University of Georgia’s Odum School of Ecology, told CNN.

Jorō spiders can get stressed out, but while their heart rates accelerate similarly to other spiders, they do not panic and run away. Instead, the arachnids "simply stay in place," Davis said, per CNN.

The spiders' remaining calm under stress could make them harder to identify when they make webs in cities, towns, buildings and human dwellings.

How did the Jorō spider study work?

The UGA researchers discovered that the Jorō spiders' ability to remain so calm under stress, with the arachnids even staying still for hours, stems from a rare freezing response previously identified in a separate 2023 study led by Davis. Compared to other arachnids in similar stressful situations, the Jorō spider maintained composure much better.

An experiment proved the Jorō spiders' innate ability and involved the researchers placing the arachnids in wood frames, where the temperature was 22 degrees Celsius, for an entire day.

"All spiders examined were indeed sitting motionless on their webs the following morning after collection and showed no indication of having moved in the hours," the study says. "We therefore considered them to be in a ‘resting’ (i.e., inactive) state."

Jorō spiders 'rarely struggled' when physically restrained

The researchers did another experiment to further their analysis, which involved physically restraining the Jorō Spiders to see their response. They carefully pinned down the spiders, thus avoiding any harm or injury, and used a microscope camera to record the arachnids' heart rates by counting heartbeats through their abdomens.

While the Jorō spiders did not struggle while restrained, one of the other three closely related arachnids (golden silk spider, yellow garden spider and banded garden spider) in the study did.

“The Jorō spiders rarely struggled once restrained, while the garden spiders put up quite a fight. I lost several of the garden spiders in the lab due to them fighting against being restrained. It was easy to find them though — I would come into the lab the next day and find large webs strung up,” Christina Vu, co-author of the study, told CNN.

'Looks like something out of a horror movie'

Since initially being sighted in Georgia in 2013 and 2014, the Jorō spiders' population in the state and other regions of the Southeast has expanded.

Researchers from Clemson University determined in a 2023 study that the species is hastily expanding outside South Carolina, and data suggests the arachnids may be found in most of the eastern U.S.

According to iNaturalist.org, Joro spiders reside primarily in Georgia but have migrated to neighboring states. They've been spotted in South Carolina, North Carolina and Tennessee, and sightings have been reported in Oklahoma, West Virginia and Maryland.

“When you have a new invasive species like this, there’s a lot of interest in how far it will spread, and what it would mean for local insects and wildlife. It doesn’t help that this particular invasive species looks like something out of a horror movie,” Vu said about Jorō spiders, per CNN.

Contributing: Janet Loehrke/ USA TODAY