Researchers have discovered more than 111,000 spiders thriving in what appears to be the world's largest spider web, deep inside a pitch-black cave on the Greek-Albanian border.
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This massive colony consists of a colossal web in a permanently dark zone of the cave, according to a study published Oct. 17 in the journal Subterranean Biology. The web stretches 106 square meters along the wall of a narrow, low-ceilinged chamber near the cave entrance. It is a patchwork of thousands of individual, funnel-shaped webs, the researchers noted.
This is the first evidence of colonial behavior in two common spider species and likely represents the largest spider web in the world, said the study's lead author István Urák, an associate professor of biology at the Hungarian Sapientia University of Transylvania in Romania.
The spider metropolis is located in the Sulfur Cave, a cave that had a sulfuric acid pit formed by the oxidation of hydrogen sulfide in groundwater. While the researchers have uncovered tantalizing new information about the Sulfur Cave spider colony, they weren’t the first to see the giant web. Speleologists from the Czech Speleological Society discovered it in 2022 during an expedition to the Vromoner Gorge. A team of scientists subsequently visited the cave in 2024, collecting samples of the web that Urák analyzed before embarking on his own expedition to the Sulfur Cave.
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This analysis revealed that two species of spiders live in the colony: Tegenaria domestica, known as the barn spider or house spider, and Prinerigone vagans. During their visit to the cave, Urák and his colleagues estimated that there were about 69,000 specimens of T. domestica and more than 42,000 specimens of P. vagans. DNA analyses for the new study also confirmed that these are the dominant species in the colony, Urák said.
The spider colony in Thiou Cave is one of the largest ever recorded, and the species involved were not previously known to congregate and cooperate in this way, Urák said. T. domestica and P. vagans are widespread near human habitations, but the colony is “a unique case of two species coexisting within the same web structure in such huge numbers,” he said.
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It is important to preserve the colony, despite the challenges that may arise from the cave's location between two countries, Urák said. In the meantime, researchers are working on another study that will reveal further evidence about the inhabitants of the Thieves' Cave, he added.
