Gentle Giants: New Study Shows Joro Spiders, Despite Their Size, are Harmless Creatures

Despite their intimidating appearance, the giant yellow, blue, and black spiders that are common throughout the southeastern United States owe their survival to a surprising trait: They’re rather shy.

According to a new study from the University of Georgia, the Jorō (Joro) spider may be the shyest spider ever documented.

“One of the ways people think this spider could affect other species is because it is aggressive and out-competes all other native spiders,” said Andy Davis, lead author of the study and a research scientist in the Odum School of Ecology at UGA. “So we wanted to get to know the personality of these spiders and see if they are capable of behaving this aggressively.

“It turns out they aren’t.”

The researchers compared the responses of more than 450 spiders to a brief, harmless disturbance across 10 different species.

While most spiders froze for less than a minute before resuming their normal activities, guru spiders remained still for more than an hour.

“They basically shut down and waited for the disruption to pass,” Davis said. “Our paper shows that these spiders are really more afraid of you than the other way around.”

In fact, Joros are relatively harmless to humans and pets. Joros will not bite unless cornered. And even if you could somehow annoy a guru into biting you, their fangs probably wouldn’t be big enough to pierce your skin.

Most spiders start moving quickly after stress, and Joros stay still for over 60 minutes

To examine the spiders’ reaction to stress, the researchers used a turkey baster to gently blow two quick puffs of air on individual spiders. This minor disturbance causes the spiders to be “frozen” for a period of time, absolutely motionless.

Researchers tested more than 30 garden spiders, ranged garden spiders and marbled circular weavers. They also analyzed similar data from previously published and peer-reviewed papers that assessed the response of an additional 389 spiders, comprising five additional species.

All those spiders started moving again after about a minute and a half of being still.

However, the Joros remained immobilized without physical or leg movement for more than an hour in most cases.

The only other spider species that showed a similar stretch response was the guru spider’s cousin, the golden silk spider. Known as Trichonephila clavipes, the golden silk spider and guru spider are the same genus.

Joros may be invasive, but they are not aggressive

Officially known as Trichonephila clavata, the East Asian Guru spider first arrived in Georgia around 2013. This species is native to Japan, Korea, Taiwan, and China, and likely arrived as well as the United States in a shipping container.

Since then the species has spread rapidly throughout the state and much of the Southeast. The number of guru spiders easily reaches into the millions now. And there is not much we can do to stop them from expanding their reach.

Davis’ previous research even suggested that invasive spiders could have spread beyond their current habitats and across much of the East Coast.

“Most people think of ‘aggressive’ and ‘aggressive’ as synonymous,” said Amic Anirau, co-author of the study and an undergraduate researcher at the university. “People were afraid of guru spiders at first, but maybe this paper can help calm people down.”

Guru spiders are built to withstand human activity

Joros are regularly spotted in areas where Georgian spiders do not normally live.

They build their golden webs between power lines, over stop lights and even over pumps at local gas stations—none of which is a particularly quiet place.

Researchers believe that guru spiders’ shyness may help them tolerate the constant barrage of noise, vibration, and visual stimuli they encounter in urban areas. Their prolonged freeze-to-stupor response can help conserve the Guru Spiders’ energy.

If you’re wondering how something so mild can spread the way Guru spiders spread, you’re not the only one.

“One of the things this paper tells me is that the rapid spread of Gurus must be due to its amazing reproductive potential,” Davis said. “They simply mate with everyone else. Not that they displace native spiders or kick them out of their own webs.”

Arachnophobes can take solace in the meek and gentle disposition of spiders. But spiders are likely to survive.

“They’re good at living with humans, and they probably aren’t going away anytime soon,” Aniraw said.

The work has been published in the journal arthropods.