Joro spiders attack and eat each other sometimes: 'Nonsexual cannibalism'

Rick Sobey, Boston Herald on Jul 11, 2025

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BOSTON — Excited for the joro spider invasion?!

Well if you’re an arachnophobe, this probably isn’t for you.

But if you’re interested in wildlife and nature, you may have a chance to watch the large black and yellow spiders attack one another as their population grows.

Researchers in a new study found that the world-infamous parachuting joro spiders will attack and eat each other in certain conditions.

“We watched what would happen if the spiders were together in a container, and it sometimes would lead to a battle to the death,” leading joro researcher Andy Davis, at the University of Georgia’s Odum School of Ecology, told the Herald.

“It’s odd because we initially thought joros were pretty shy based on our previous work,” he added. “So we believe they have a shy personality, but they apparently can be aggressive to each other.”

Based on some initial sightings of spiders trapping other spiders in their webs, the University of Georgia scientists conducted a lab test where they placed two female joro spiders together in a container, and monitored their behavior.

In some, but not all cases, one female attacked the other and then ate it. The researchers even found that this happens when they placed two spiders on the same web in the field.

A giant joro spider was confirmed in Boston for the first time last year — the first confirmed joro sighting in Massachusetts, and the most northern sighting yet. The big female spider was spotted in Beacon Hill.

The massive spiders have been spreading for years across the Southeast, where there are now millions of the eight-legged creatures. Davis has hundreds of the spiders and their massive webs in his backyard.

This study could have major implications for controlling its population.

“Given that they’ll eat each other, it implies that if their densities get really high, they may kill off their own competition,” Davis said. “They have the ability to lower their own population.”

In Georgia, there has been some evidence that where joro spiders are abundant, the region can see declines in other native spider species.

The new research paper in the journal Arthropoda is titled, “It’s a Spider-Eat-Spider World: Observations of Nonsexual Cannibalism in the Invasive Joro Spider.”

“Spiders and other arthropods can sometimes consume others of their kind, and this is most often associated with mating activity, whereby females cannibalize males during or after mating, or during mating attempts,” the study reads. “Nonsexual cannibalism is less common but may be associated with food availability or territorial aggression… Here, we report descriptive observations and photo-documentation of nonsexual cannibalism by this species.”

In the cases where cannibalism was witnessed, it involved one female biting and killing another, typically after a short fight.

When two females of a similar size were placed together in a container, fights ensued 40% of the time. When females of different sizes were paired, fights happened 18% of the time, and the larger females were not always the aggressor.

Across all the lab trials, six bouts (9%) led to the direct killing of one female.

In field trials where two females were placed on an empty web, researchers saw one fight (7%) where the aggressor ended up killing and wrapping the other spider in silk.

“The observations here suggest these spiders are capable of a surprising level of intraspecific aggression,” the study reads. “From these observations, we conclude that females of this species can be hostile to other females.”

The attacks could happen when the female spiders are provoked or stressed, according to the researchers.

University of Georgia students Kade Stewart, Caitlin Phelan and Alexa Schult observed the spiders during the study.

More of the giant spiders could come up to the Northeast this year, Davis said.

“It wouldn’t surprise me at all,” he added.

The researcher had previously predicted that joro spiders would move up the East Coast because they’re really good at hitching rides on cars.

Officially known as Trichonephila clavata, the East Asian Joro spider first arrived in Georgia around 2013. The species is native to Japan, Korea, Taiwan and China, and likely hitched a ride stateside on a shipping container.

If you pick one up, the spider might try to bite you. But its fangs likely wouldn’t be large enough to pierce your skin.

“They’re no more dangerous than any backyard garden spider,” Davis said.

The spiders are known to eat flies and mosquitoes, along with native pollinators like bees.