Urak et al. 2025, Subterranean Biology
The giant web is inhabited by more than 111 thousand spiders of two different species and is 106 square meters.
In a dark cave with the smell of sulfur, located on the border between Albania and Greece, scientists discovered what could be the largest spider web on Earth. The extensive 106 square meter web is inhabited by more than 111 thousand spiders, making it technically large enough to catch a whale.
The extraordinary discovery was detailed in a publication last month in the journal Subterranean Biology and marks the first record of large-scale colonial behavior in two species of spiders thought to be solitary.
The web was discovered in the Sulfur Cave, a low-ceilinged cave formed by the slow erosion of the rock by sulfuric acid generated by underground gases. The web itself is a huge patchwork blanket composed of thousands of interconnected funnel-shaped webs, forming what lead researcher István Urák, a biologist at the Hungarian Sapientia University of Transylvania, described as a “megacity of spiders”.
“The natural world still holds countless surprises,” Urák told . “Being in front of a structure like this fills us with admiration, respect and gratitude — you have to experience it to truly understand it.”
The site was discovered in 2022 by members of the Czech Speleological Society, but it was not until 2024 that Urák and an international team of researchers carried out a detailed investigation. By collecting and analyzing specimens, scientists identified two species living together in the colony: a Tegenaria domestica (the house spider or funnel spider) and the Prinerigone vagans. Around 69,000 T. domestica and 42,000 P. vagans were recorded, cohabiting in numbers and with cooperation never before observed in these species.
Normally, T. domestica predation P. vagansbut researchers suggest that the cave’s permanent darkness could impair vision and alter predatory behavior. Instead, both species feed on non-biting mosquitoes, which thrive in microbial biofilms produced by sulfur-oxidizing bacteria that live in the cave’s hydrogen sulfide-rich stream.
The spiders’ unusual diet altered their biology. DNA and microbiome analyzes revealed that the spiders that inhabit the cave have less diverse gut bacteria and present genetic differences in relation to their surface relatives, indicating adaptation to the hostile environment of the cave.
“This discovery shows how even familiar species can exhibit remarkable flexibility in extreme conditions,” said Urák.
Scientists highlight the importance of preserving the Gruta do Enxofre ecosystem, despite the jurisdictional challenges posed by its transboundary location.
