Discovery: Scientists documented a communal spiderweb covering 1,140 sq ft (106 m²) inside Sulfur Cave on the Albanian–Greek border that hosts about 111,000 spiders. Species: The colony is dominated by Tegenaria domestica (~69,000) and Prinerigone vagans (>42,000). Ecology: Spiders feed on midges that graze sulfur-oxidizing microbial biofilms, and genetic and microbiome data suggest cave populations are adapted to the dark, sulfurous environment. Conservation: Researchers urge protection and plan follow-up studies.
World’s Largest Communal Spiderweb Found in Sulfur Cave — 111,000 Spiders Living in Pitch-Black Colony
Discovery: Scientists documented a communal spiderweb covering 1,140 sq ft (106 m²) inside Sulfur Cave on the Albanian–Greek border that hosts about 111,000 spiders. Species: The colony is dominated by Tegenaria domestica (~69,000) and Prinerigone vagans (>42,000). Ecology: Spiders feed on midges that graze sulfur-oxidizing microbial biofilms, and genetic and microbiome data suggest cave populations are adapted to the dark, sulfurous environment. Conservation: Researchers urge protection and plan follow-up studies.
02:08, 05.11.2025Science
Record-breaking communal spiderweb discovered in Sulfur Cave on the Albanian–Greek border
Researchers have documented an extraordinary communal spiderweb deep inside Sulfur Cave, a cavern shaped by sulfuric acid along the Albanian–Greek border. A study published Oct. 17 in the journal Subterranean Biology reports a mosaic of thousands of funnel-shaped webs covering 1,140 sq ft (106 m²) of cave wall and hosting roughly 111,000 spiders.
The massive colony was first reported by cavers from the Czech Speleological Society during a 2022 expedition. Scientists visited the site in 2024 to collect specimens; follow-up analyses led by István Urák, an associate professor of biology at Sapientia Hungarian University of Transylvania, confirmed the composition and scale of the community.
Species and structure: DNA and field estimates indicate the colony is dominated by two species: Tegenaria domestica (the barn funnel weaver or domestic house spider) — about 69,000 individuals — and Prinerigone vagans — more than 42,000. Rather than one continuous sheet, the communal web is a close-packed patchwork of thousands of individual funnel-shaped webs woven into a single large structure along the passage wall.
How the colony survives: The cave hosts a sulfur-rich stream fed by natural springs. Sulfur-oxidizing bacteria form white microbial biofilms on cave surfaces; non-biting midges feed on those biofilms, and the spiders prey mainly on the midges. This food chain sustains the dense colony despite permanent darkness.
Adaptation and microbiomes: Gut-content and molecular analyses show the cave spiders’ diets and microbiomes differ markedly from surface relatives. The cave spiders have significantly less diverse microbiomes and display genetic differences from outside populations, suggesting they have adapted to the cave’s dark, sulfurous conditions.
“Often, we think we know a species completely... yet unexpected discoveries can still occur,” Urák said, noting that extreme environments can reveal genetic plasticity and unusual behaviors.
Conservation and next steps: Urák and colleagues emphasize the importance of protecting this unique colony, though conservation efforts are complicated by the cave’s cross-border location. The research team is preparing follow-up studies to clarify how the spiders coordinate in such high densities, how their genomes have shifted, and what protections are needed to preserve the site.
Note: All figures and observations referenced here are from the Oct. 17 publication in Subterranean Biology and field expeditions described above.