Fort Worth Star-Telegram
111,000 Spiders Built a Web Across Two Countries and Yes, It's as Terrifying as It Sounds
By Ryan Brennan
March 31, 2026 12:30 PM
Picture a spiderweb roughly half the size of a tennis court. Now put it deep inside a cave that straddles the border of two countries — and fill it with 111,000 spiders from two species that normally eat each other.
That’s exactly what researchers found inside the Sulfur Cave in the Vromoner Canyon, located on the border of Greece and Albania.
Their findings, published in the journal Subterranean Biology in October 2025, describe what might be the world’s largest spiderweb — and the bizarre truce happening inside it.
A Blanket-Like Spiderweb Hidden in Total Darkness
The web was first observed in 2021 by cavers from the Czech Speleological Society. Marek Audy, who originally discovered the spiderweb, described it as “dense” and “like a blanket.”
Located 50 meters (164 feet) from the cave entrance in a permanently dark section, the web stretches along a narrow, low-ceilinged passage and measures 106 square meters (1,140 square feet).
According to Audy, it’s built from a multi-layered patchwork of individual funnels that form a spongy mass.
“When there’s danger, the female crawls back and hides, and no creature of a higher order can dig her out of there,” Audy said.
Two Unlikely Spider Species Living In Harmony
Here’s where it gets truly strange. Researchers estimated spider numbers by counting individual web funnels and collecting specimens for further analysis.
What they found were two species sharing the web: roughly 69,000 Tegenaria domestica (barn funnel weavers, also known as common house spiders) and 42,000 Prinerigone vagans spiders.
Under normal circumstances, barn funnel weavers prey on the smaller Prinerigone vagans. So why aren’t they attacking each other?
Researchers believe the cave’s poor lighting impairs the spiders’ vision, creating an unlikely truce between the species.
Dr. Lena Grinsted, a senior lecturer at the U.K.’s University of Portsmouth who was not a part of the study, offered some context.
“Spiders, in general, are not particularly good at seeing stuff … and that includes these two species,” she told the Associated Press.
There’s also the matter of food. An estimated 2.4 million midge flies buzz around the Sulfur Cave spider colony, giving the spiders a never-ending supply of food.
Researchers think the food supply, combined with the darkness, limits the hostility between species.
“So often if you have spiders in close vicinity, they will fight and end up eating each other,” said Dr. Grinsted. “We can sometimes see that if there’s an abundance of food that they sort of become a bit less aggressive.”
Still, don’t imagine these spiders as friendly neighbors.
While the spiders likely work together in building the web, Grinsted said it’s “highly unlikely that they cooperate in anything else like prey capture, in brood care, or looking after each other’s babies.”
A Spider Colony With Similar, Yet Different, Relatives
Upon further analysis, researchers discovered something else surprising: the spiders inside the cave are genetically different from those found outside.
“The DNA is interesting because they revealed that the species which live inside the cave is different from the one which lives outside the cave,” Dr.
Blerina Vrenozi, a biologist and zoologist at the University of Tirana in Albania who co-authored the study, told the Associated Press. “So it’s the same species, but different DNA,” she added.
Their sulfur-rich diet has significantly reduced the diversity of their gut microbiomes. Both findings suggest the colony does not mix with outside spider populations — they’ve adapted exclusively to cave life.
So the next time a cobweb in the corner of your ceiling gives you a shiver, consider this: somewhere beneath the mountains between Greece and Albania, 111,000 spiders are quietly coexisting in total darkness.
And the blanket of silk they’ve been creating is rewriting the rules of spider behavior.
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