New study finds invasive Jorō spiders ‘keep cool under pressure’

By Taylor Nicioli, CNN

(CNN) — Spiders have a reputation for giving some humans a fright, but a team of scientists has flipped the script to learn why one increasingly visible species seems to have an edge on handling stress.

Jorō spiders — which have been spreading across the southeastern United States since their first appearance in the country in 2013 — don’t appear to have many limits as to where they build their webs and have been known to take shelter on top of streetlamps and on buildings near frequent human disturbances. To find out why the spider is so tolerant of urban settings, researchers with the University of Georgia investigated the best indicator of its stress levels: its heart rate.

“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,’” said lead author of the research Andy Davis, a research scientist at the University of Georgia’s Odum School of Ecology.

“It turns out that they do get stressed — their heart rates accelerate just as much as other spiders do — but instead of panicking and trying to run away every time they get stressed, they simply stay in place. … It seems like even though their heart rate does accelerate, it’s much more even (than the other spider’s heart rates),” he added. “They keep cool under pressure.”

The new study, published Monday in the journal Physiological Entomology, found that Jorō spiders’ ability to withstand stress comes down to a rare freezing response previously identified in a 2023 study also led by Davis. The fact that the spiders froze, or stayed still, for over an hour when disturbed caused their heart rates to stay more steady compared with the fluctuating rates of other species of spiders in the same situation.

To test the spiders’ heart rates, Davis and study coauthor Christina Vu, who was a University of Georgia undergraduate student of entomology at the time, wrangled 79 spiders from two different genera. They compared the Jorō (scientifically known as Trichonephila clavata) to a closely related spider in the same genus known as the golden silk spider (T. clavipes), which also freezes under stress, as well as two similarly sized species from the Argiope genus, the yellow garden spider (A. aurantia) and the banded garden spider (A. trifasciata).

The researchers had to carefully pin down and restrain the spiders, without causing harm or injury, they noted in the study, to capture the creatures’ heart rates using a microscope camera to manually count the spiders’ heartbeats through the arachnids’ abdomens. They compared the spiders’ resting heart rates to their heart rates during restraint and found all the spiders’ heart rates increased, but the Argiope spiders, which are known to avoid urban settings, had many more spikes as they struggled to run away, according to the research.

“The Joro 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,” Vu said in an email.

Invasive Jorō spider spread

Native to east Asia, Jorōs were first spotted in the US in Georgia over 10 years ago and have since spread to surrounding states such as West Virginia, Tennessee and even as far north as Maryland, Davis said. It is hard to tell how far the spiders have spread so far this year, since most sightings come in the fall when the spiders’ spring babies reach their full size.

Several prior studies have also found the spider to be more tolerant to colder climates than the golden silk spider, which cannot spread beyond the Southeast due to its vulnerability to the cold. In contrast, the Jorō could spread and survive as far northeast as Canada, Davis said.

“I would hazard to guess at some point years from now, there’ll be sightings of (Jorō) spiders all over the US and in Canada,” he said. “It looks like they can physiologically live pretty much anywhere in the US, and, at least southern Canada.”

Unfortunately for arachnophobes, Jorōs seem to “prefer to build webs in closer proximity to manmade structures and have a strong tolerance for areas of high vibration and wind disruption,” said Floyd Shockley, collections manager for the department of entomology at the Smithsonian National Museum of Natural History in Washington, DC, who was not part of the new study. He found the research “very interesting and another piece of the puzzle as to why Jorōs do so well in habitats that are often less optimal for other web-building species.”

“The fact that their reaction to physical non-lethal stress and not to struggle when restrained suggested that they would be more successful in these habitats compared to other species,” Shockley added in an email.

While the study focused on the spiders’ reaction to restraint, further research on the species’ response to other stressors, such as cold temperature, could also help to explain why it is able to gradually spread as it currently is, he said.

More research on the Jorō spider

It is possible that the spider’s freeze response could be an advantage when faced with a predator that might be less likely to eat something that is still, said Jay Stafstrom, a postdoctoral researcher at Cornell University in Ithaca, New York, who was not part of the study. But he said more research would be needed to know exactly why the spiders respond in that way.

“It might be that most of those really big spiders in this genus may be just really chill, but it’s hard to know why or if there is some function to it, maybe it’s just that they’re bigger and so they move less,” Stafstrom said.

“What you can actually say from the work that they did is that the spiders that struggle when they’re restrained have more variable heart rate. Which totally makes sense. But then … to say that this might help them become more urban and expand more across the US is a jump,” he added. “It certainly could be a piece of the puzzle, but without actually testing urban stressors and then showing that spiders are doing better or worse at being in urban environments … I think it’s a bit early to make that jump.”

But testing a spider’s stress response to natural disturbances, such as a nearby predator like a bird or a car whizzing by, would be near impossible, Davis said.

“We did only subject the spiders to one type of stressor (restraint) in our lab, and so we don’t know if the types of stressors and stimuli they would experience in an urban setting would be equally as stressful to the spiders. … To observe spider heart rates, they must be restrained in the first place, which causes a heart rate elevation,” he said.

“How could we ever test if urban stimuli cause spiders to be stressed, without actually causing the stress? Believe me, I’ve tried to measure heart rates of spiders in the wild, as in, while they were on their web. It is hard,” added Davis, who was also the lead author of a February 2024 study that found the spiders to not be greatly affected by the noise and wind disturbance of roadsides when catching and eating prey.

While further study is needed to know exactly why the Jorō has its unique traits, researchers are also interested in the invasive spider’s impact on the ecosystem. Time will tell whether Jorōs are outcompeting native species that have similar diets, Davis said. As of now, those who are looking to relocate a Jorō spider taking up space in their backyards can rest easy knowing that they are fairly docile and easy to move, he added.

“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.

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