Timid Joro Spiders Multiply Across the US without Causing Alarm

by Henrik Andersen
Joro spiders

Caption: A female Joro spider, depicted with a 30mm scale bar for size reference. Image Credit: Jeremy Howell

Recent research reveals that the large Joro spiders, despite their imposing appearance, pose no harm and exhibit a remarkably shy nature.

Contrary to concerns that these yellow and blue-black spiders, which are increasingly populating the Southeastern United States, might be aggressive and outcompeting native species, a study conducted by the University of Georgia suggests otherwise.

Lead author Andy Davis, a research scientist at UGA’s Odum School of Ecology, explains, “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. It turns out they’re not.”

In an examination involving more than 450 spiders across ten different species, researchers found that when subjected to a brief and harmless disturbance, most spiders froze for less than a minute before resuming their normal activities. However, Joro spiders remained motionless for over an hour.

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

Moreover, Joro spiders are relatively harmless to humans and pets. Unless cornered, they will not bite, and even if they were to bite, their fangs are unlikely to penetrate the skin.

To gauge the spiders’ response to stress, researchers gently blew two rapid puffs of air onto individual spiders using a turkey baster. This minor disturbance caused the spiders to freeze completely for a period of time.

While garden spiders, banded garden spiders, and marbled orb weavers quickly resumed movement after about a minute and a half, Joro spiders remained frozen with no body or leg movement for over an hour in most cases. The only other species displaying a similar prolonged response was the golden silk spider, a cousin of the Joro spider belonging to the same genus.

Despite being an invasive species, the Joro spider’s behavior does not indicate aggression. Native to Japan, Korea, Taiwan, and China, the East Asian Joro spider first arrived in Georgia around 2013, likely transported through shipping containers. Since then, the species has rapidly spread throughout the state and the Southeast, with their population now reaching millions.

Amitesh Anerao, co-author of the study and an undergraduate researcher at the university, notes, “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.”

Joro spiders are frequently observed in areas where native Georgia spiders do not typically reside, such as building their golden webs between powerlines, atop stoplights, and even above gas station pumps—environments characterized by noise, vibrations, and visual stimuli. The researchers suggest that the spiders’ timid nature may aid their survival in urban settings, as their extended freeze response conserves energy.

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

While arachnophobes may find solace in the meek and gentle temperament of the Joro spiders, it is likely that these spiders will remain a permanent presence due to their adaptability to coexist with humans.

Anerao concludes, “They’re so good at living with humans that they’re probably not going away anytime soon.”

Reference: “Startle Responses of Jorō Spiders (Trichonephila clavata) to Artificial Disturbance” by Andrew K. Davis and Amitesh V. Anerao, 15 May 2023, Arthropoda.
DOI: 10.3390/arthropoda1020009

Frequently Asked Questions (FAQs) about Joro spiders

Are Joro spiders dangerous to humans?

Joro spiders are relatively harmless to humans. They typically won’t bite unless cornered, and even if they do bite, their fangs are not large enough to pierce the skin.

Do Joro spiders exhibit aggressive behavior?

Contrary to their intimidating appearance, Joro spiders are actually quite timid. Research has shown that they are more afraid of humans than the other way around. They tend to freeze and remain motionless when disturbed, rather than displaying aggression.

How are Joro spiders impacting native spider species?

Contrary to initial concerns, Joro spiders’ rapid spread is not due to aggressive displacement of native spider species. Instead, their success is primarily attributed to their high reproductive potential, outbreeding other spiders and increasing their population.

Can Joro spiders be controlled or eradicated?

Unfortunately, Joro spiders have already established themselves in the Southeastern United States and are rapidly spreading. Controlling their population or eradicating them entirely is challenging, so they are likely to remain a permanent presence in these areas.

Where are Joro spiders commonly found?

Joro spiders are frequently observed in urban settings, often building their webs in unusual locations such as powerlines, stoplights, and gas station pumps. They have adapted to withstand noise, vibrations, and visual stimuli commonly found in these environments.

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NatureWatcher23 July 11, 2023 - 11:43 am

joro spiders are incredible! they’re adapting to urban life, building webs in crazy places. maybe their timidity helps them deal with all the noise and vibrations. fascinating creatures!

ArachnoFanatic July 11, 2023 - 6:37 pm

Joro spiders r taking over the south. but they not bad spiders! they freeze for long time when disturbed. they just timid and scared. no biggie!

BugHunter22 July 11, 2023 - 8:12 pm

i was so scared of joro spiders at first! but this research calms me down. they won’t bite u unless cornered. and their fangs probs can’t pierce ur skin. no worries, they shy lil guys.

SpideySense July 12, 2023 - 3:31 am

who knew joro spiders are shy spiders? they just freeze when startled. not aggressive at all. but they’re spreading fast, so we’ll be seeing more of them. gotta learn to live with these little buddies!


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