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Joro spiders: They may be massive, but they are gentle giants

Don’t judge a book by its cover, or a spider by its size and color, for that matter. The intimidating giant yellow and blue-black Jorō spiders, which have been spreading across the Southeastern United States, are not as fearsome as they seem. They owe their survival to a rather unexpected trait: timidity.

The University of Georgia recently published a study shedding light on the behavior of these creatures. The research is published in the journal Arthropoda.

According to Andy Davis, the lead author of the study and a research scientist at UGA’s Odum School of Ecology, the Jorō spider may be one of the least aggressive spiders ever documented.

“One of the ways that people think this spider could be affecting other species is that it’s aggressive and out-competing all the other native spiders. So we wanted to get to know the personality of these spiders and see if they’re capable of being that aggressive,” explained Davis. His research uncovered a surprising truth: Jorō spiders aren’t aggressive at all.

How the research was done

In an intriguing experiment, Davis and his team compared the responses of more than 450 spiders from 10 different species to a brief, harmless disturbance. Instead of bouncing back quickly, the Jorō spiders played dead for an extended period.

“They basically shut down and wait for the disturbance to go away. Our paper shows that these spiders are really more afraid of you than the reverse,” said Davis. 

In fact, the Jorō spiders, despite their formidable appearance, pose little threat to humans or pets. They only bite when cornered, and their fangs are typically too small to pierce human skin.

To study the spiders’ reaction to stress, the researchers gently blew two rapid puffs of air onto individual spiders using a turkey baster. 

This action caused the spiders to freeze in place. Various species, including garden spiders, banded garden spiders, and marbled orb weavers, were tested. The team also included data from previous peer-reviewed studies that evaluated the response of additional species.

The spiders all demonstrated a brief freeze response, going motionless for about a minute and a half on average. The Jorō spiders, however, remained motionless for over an hour, displaying an unusually extended freeze response. 

The only other species displaying a similar reaction was the Jorō’s cousin, the golden silk spider, both belonging to the same genus, Trichonephila.

Joro spiders are quickly expanding their habitat

The Jorō spider, officially named Trichonephila clavata, originally hails from East Asia, specifically Japan, Korea, Taiwan, and China. It is believed that the species first arrived in Georgia around 2013, likely as unintended passengers on a shipping container.

Since then, the Jorō spiders have spread rapidly across Georgia and the Southeast. Their numbers are now in the millions, and it seems there’s little that can be done to halt their increasing range.

Study co-author Amitesh Anerao noted: “Most people think ‘invasive’ and ‘aggressive’ are synonymous. People were freaking out about the Joro spiders at first, but maybe this paper can help calm people down.”

Interestingly, Jorō spiders have a knack for occupying spaces where native Georgia spiders rarely venture. They weave their golden webs in high-traffic areas such as between power lines, atop stoplights, and even above gas station pumps.

What the researchers learned

The researchers suspect that the Jorō spiders’ shyness could be a survival strategy in urban environments, allowing them to withstand the constant noise, vibrations, and visual stimuli. Their extended freeze response when startled may be a means of conserving energy.

If you’re puzzled as to how such a timid creature could spread so rapidly, you’re not alone in your curiosity. Davis points to the spiders’ remarkable reproductive capabilities to explain their rapid proliferation. 

“One thing this paper tells me is that the Joros’ rapid spread must be because of their incredible reproductive potential,” said Davis. “They’re simply outbreeding everybody else. It’s not because they’re displacing native spiders or kicking them out of their own webs.”

This doesn’t mean that the timid Jorō spiders are pushing native spiders out of their habitats. Instead, they’re simply expanding their own territories and reproducing at a faster pace.

For those with a fear of spiders, the knowledge of the Jorō spiders’ mild and gentle nature might offer some comfort. However, it’s essential to remember that these creatures are likely here to stay. “They’re so good at living with humans that they’re probably not going away anytime soon,” said Anerao.

So next time you come across a Jorō spider in an unexpected place, remember this: the spider is likely more scared of you than you are of it. And far from being an aggressive invader, this timid arachnid is just trying to survive in its new environment.

More about spiders

Spiders are air-breathing arthropods that are found all over the world. As of my knowledge cutoff in September 2021, there are more than 48,000 known species of spiders, and scientists suspect there may be many more undiscovered species.

Spiders are a part of the order Araneae, which is divided into two suborders: Mesothelae, which contains the primitive spiders, and Opisthothelae, which includes the more modern spiders. The Opisthothelae is further divided into two groups: Mygalomorphae, the tarantulas and their kin, and Araneomorphae, the remaining spiders.

These creatures are best known for their ability to spin silk. They use this silk for various purposes, including constructing webs to catch prey, creating egg sacs, and making shelter. Some spiders don’t use webs to hunt, instead relying on camouflage and speed to catch their prey.

Spiders are carnivorous and typically feed on insects, although some larger species have been known to eat small mammals, birds, and reptiles. They employ a range of hunting strategies, from lying in wait to actively pursuing or even tricking their prey. The majority of spiders use venom to subdue their prey. However, very few spider species are dangerous to humans.

Spiders reproduce by laying eggs. The males of most species use a modified pair of appendages, called pedipalps, to transfer sperm to the female. In many species, the females are larger than the males, and it’s not uncommon for female spiders to eat their mates, a behavior that has made the “black widow” spider infamous.

Spiders have a unique leg structure that sets them apart from insects. They possess eight legs (compared to insects, which have six), and their bodies are divided into two segments: the cephalothorax (which combines the head and thorax) and the abdomen.

Spiders have a significant impact on ecosystems. They help control insect populations, and they are also a food source for many birds and small mammals. Despite their sometimes fearsome appearance and reputation, spiders play an essential role in maintaining the balance of nature.


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