Imagine stumbling upon a sprawling metropolis of spiders, hidden in the depths of a sulfur-rich cave, where over 111,000 arachnids thrive in complete darkness. This isn’t a scene from a horror movie—it’s real. Researchers have uncovered what may be the world’s largest spiderweb, nestled deep inside Sulfur Cave on the Albanian-Greek border, and it’s rewriting everything we thought we knew about spider behavior.
But here’s where it gets controversial: this isn’t just any spider colony. It’s the first documented evidence of two common spider species—Tegenaria domestica (the barn funnel weaver) and Prinerigone vagans—living together in a single, massive web structure. These species are typically found near human dwellings, but their coexistence in such staggering numbers is unprecedented. István Urák, the study’s lead author and an associate professor of biology at Sapientia Hungarian University of Transylvania, calls it a ‘unique case’ that challenges our understanding of spider social dynamics.
And this is the part most people miss: the cave’s extreme environment has reshaped these spiders’ biology. The lack of light may have impaired their vision, altering their hunting habits. Instead of preying on each other, as expected, they feast on non-biting midges, which in turn feed on microbial biofilms from sulfur-oxidizing bacteria. This sulfur-rich diet has even influenced their microbiomes, making them less diverse than their cousins outside the cave. Genetic analyses reveal that these cave-dwelling spiders have evolved differently, adapting to their harsh, sulfur-filled home.
The discovery began in 2022 when cavers from the Czech Speleological Society first stumbled upon the web during an expedition in Vromoner Canyon. Scientists later visited the cave in 2024, collecting specimens that Urák analyzed before leading his own expedition. The team estimated the colony includes approximately 69,000 T. domestica and over 42,000 P. vagans, with DNA analyses confirming their dominance.
‘The natural world still holds countless surprises for us,’ Urák told Live Science. ‘When I saw the web, I felt admiration, respect, and gratitude. It’s something you have to experience to truly understand.’
Sulfur Cave itself is a marvel, carved out by sulfuric acid from the oxidation of hydrogen sulfide in groundwater. A sulfur-rich stream flows through it, creating an ecosystem that supports microbes, midges, and their spider predators. But preserving this colony won’t be easy—the cave sits on the border of two countries, raising logistical and political challenges.
Here’s a thought-provoking question: Should we prioritize protecting this unique colony, even if it means navigating complex international cooperation? And what does this discovery tell us about the adaptability of species in extreme environments? Let’s discuss in the comments—do you think this colony deserves special protection, or is it just another natural curiosity? One thing’s for sure: this spider megacity is a reminder that nature still has secrets waiting to be uncovered.
