How Giant Joro Spiders Can Spin Webs Strong Enough to Catch Birds

Scientists have figured out the mechanisms that enable massive Joro spiders to spin their impressively strong webs, which are capable of snagging creatures as big as birds.

A team of researchers from China's Southwest University published a paper in the journal Nature Communications that revealed a hierarchical mechanism by which the spiders make their dragline web silk, allowing them to capture prey.

The researchers believe their work could hold important lessons for industry, allowing humans to create improved spider-inspired synthetic silks.

The researchers found that Joro spiders (Trichonephila clavate) have a specific order in which they synthesize the proteins and other chemicals needed to make spider silk, using their specialized major ampullate gland (the Ma gland).

joro spider webs
Stock image of a Joro spider. The web of a Joro spider is very strong, and is made by a complicated hierarchical process. iStock / Getty Images Plus

This gland has three sections: a tail, a sac, and an elongated duct. The researchers found that in the three different sections of the Ma gland, there is a hierarchical biosynthesis of substances like spidroins (the main proteins that make up spider silk), organic acids, and fats.

"To our knowledge, this study is the first to reveal the biological mechanism of silk spinning in spiders in such detail," the authors wrote in the paper, saying they believed their research "will facilitate the understanding of the spider silk-spinning process in spiders and further serve as a powerful platform for evolutionary studies of silk-spinning organisms."

"More importantly, the significant molecular characteristics revealed by our results and the generated datasets should ultimately pave the way for producing optimized synthetic silks through genetic and biomimetic manipulations," they wrote, adding that their data should "ultimately benefit innovation in spider-inspired fibers."

Joro spiders are brightly colored, with yellow and black stripes, and can grow up to three inches long. Native to Japan, Korea, Taiwan, and China, Joro spiders are an invasive species in the U.S., having been first reported in 2014. They hunt prey using their large webs made of golden or yellow-looking silk.

"[Regarding Joro spider] silk production: this [new] work is an extension of many many studies, 'just' drilling down deeper," Fritz Vollrath, a professor and spider silk expert at the University of Oxford, told Newsweek.

"Nothing special about the Nephila/Joro spider's web, just bigger and stronger than others, because the spider is bigger than most and the web architecture adapted to its habitat," he said.

Joro spiders' webs are so large and strong that they have been seen to snag birds.

"[My study on Joro spider web strength discussed in National Geographic in 2022] showed how the webs were strong enough for a bird to sit on, not catch, per se," Andy Davis, an assistant research scientist at the Odum School of Ecology at the University of Georgia, told Newsweek.

He found that the webs were capable of holding weights of up to 69 grams, or 2.4 ounces. The average red cardinal bird weighs 1.5 ounces.

"In that study we documented a full-grown female cardinal who sat on a Joro web and stole food bits from the web! Then she flew away."

According to Davis, this observation does reveal just how strong the webs are, as they are strong enough to "hold" a bird up.

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Joro spider on its web. iStock / Getty Images Plus

"This may or may not translate to being able to capture a bird. I think while it is technically possible for Joros to capture a bird, it is highly, highly unlikely that this would happen. I know of one or two instances where their close cousin, the golden silk spider, has been recorded to "capture" a small songbird, but in those instances the bird had merely gotten trapped and then died. The spider didn't necessarily intend to capture the bird."

"Given the millions of Joro webs in Georgia now, plus the millions of golden silk webs across the south, we would have seen [Joro webs capturing birds] by now if it happened with regularity."

The new research shows the detailed mechanisms behind how the Joros can make their strong silk using their specialized sectioned Ma gland and the intricate order of operations of synthesizing proteins, acids and fats.

"I can tell you that one of the things that contributes is the fact that they make more of a three-dimensional web compared to most orb-weavers. The webs have multiple support strands compared to other webs. Plus the fact that their silk strands are already so very strong, these combined make for a very, very strong web," Davis said.

Unluckily for the birds of the U.S., one 2022 study published in the journal Physiological Entomology said that the Joro spider could be expected to spread beyond its current range, which only covers the southeastern corner of the U.S., for now.

"The other thing that people need to hear is that these spiders are here to stay. At this point, there is no stopping their spread," Davis previously told Newsweek. "And, even if people go out of their way to kill every one they see in their yard, they will simply be back the next year. I've been telling people to learn to live with them. That's a tough sell, though."

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