In a pitch-black cave along the border of Greek and Albania, researchers discovered a 1,140-square-foot spider web that houses two spider species — an unprecedented example of cohabitation.
Urák et al. 2025, Subterranean BiologyA member of the research team standing next to the world’s largest spider web.
Arachnophobes beware: Scientists have discovered the world’s largest spider web in a pitch-black cave along the Albanian-Greek border.
This “extraordinary” — and frankly horrifying — web stretches a staggering 1,140 square feet and houses more than 110,000 arachnids of two different species.
In a study recently published in the journal Subterranean Biology, researchers noted that these particular spiders are not typically social creatures. As such, this discovery may also be the first example of the two arachnid species forming a colony.
An Unprecedented Colony Of Spiders Living In Sulfur Cave
The massive web stretches along the wall of a low, narrow passage near the entrance of Sulfur Cave, a cavern hollowed out by sulfuric acid. The structure comprises thousands of individual, funnel-shaped webs woven together into a single massive patchwork located in a perpetually dark area of the cavern.
“The natural world still holds countless surprises for us,” István Urák, the study’s lead author and a biology professor at Sapientia Hungarian University of Transylvania in Romania, told Live Science.
“If I were to attempt to put into words all the emotions that surged through me,” Urák said, “I would highlight admiration, respect, and gratitude. You have to experience it to truly know what it feels like.”
Urák et al. 2025, Subterranean BiologyThe barn funnel weaver spider, T. domestica, in Sulfur Cave.
Two spider species coexist within the colony: Tegenaria domestica, commonly known as the barn funnel weaver or domestic house spider, and Prinerigone vagans. Researchers estimated that approximately 69,000 T. domestica and 42,000 P. vagans specimens inhabit the web.
“What’s fascinating here is, firstly, that there is a group of communally living spiders in a cave,” Jason Dunlop, a curator of arachnids and myriapods at the Berlin Natural History Museum, told Metro.
“Most spiders are solitary,” Dunlop continued, “but a few species are known to live in groups, although these usually build large communal webs outdoors covering a whole tree or bush.”
Moreover, while both T. domestica and P. vagans are widespread near human dwellings, their collaborative living is unprecedented behavior.
“What’s really unexpected is that two rather different species of spider from two different families are involved,” Dunlop added. “That’s unique as far as I’m aware.”
The discovery of the web is also revealing new information about the diets of these spider species.
New Insights Into The Spiders’ Diets
The discovery is continuing to challenge existing knowledge about these species. Scientists would typically expect barn funnel weavers to prey on P. vagans.
Instead, T. domestica was found to be dining on tiny, non-biting midges. Researchers believe that the cave’s total darkness may impair the spiders’ vision, preventing such predation. The sheer amount of available food may also be a contributor to their change in diet.
Urák et al. 2025, Subterranean BiologyThe darkness of the cave might explain the spiders’ cohabitation.
“What the authors of the study are suggesting here is that this very unusual arrangement is only possible because there is an abundance of small flies in the cave, which means there is food enough for everyone, even when living at impressive densities of tens of thousands of individuals,” Dunlop said.
“Often, we think we know a species completely, that we understand everything about it, yet unexpected discoveries can still occur,” Urák told Live Science. “Some species exhibit remarkable genetic plasticity, which typically becomes apparent only under extreme conditions. Such conditions can elicit behaviors that are not observed under ‘normal’ circumstances.”
Urák also emphasized the importance of preserving the colony, though its location straddling two countries presents potential challenges. That said, the researchers are preparing another study that will provide additional insights into Sulfur Cave’s creepy-crawly inhabitants.
After seeing the world’s largest spider web, learn about the terrifying camel spider. Or, meet the Goliath birdeater, the heaviest spider species in the world.
