Explorers found the largest-known spider web — a >1,040 sq ft “megacity” of roughly 111,000 spiders — inside a sulfur cave on the Albania–Greece border. Chemical analyses show the spiders feed on midges that rely on sulfur-oxidizing microbes, linking the arachnids to a chemoautotrophic food chain. Genetic data indicate these cave populations are diverging from surface relatives, and researchers suggest isolation plus a reliable food source may have promoted the evolution of colonial behavior. The study is reported in Subterranean Biology (Oct. 17, 2025).
World’s Largest Spider Web Found in Sulfur Cave — 111,000 Spiders Build an Underground “Megacity”
Explorers found the largest-known spider web — a >1,040 sq ft “megacity” of roughly 111,000 spiders — inside a sulfur cave on the Albania–Greece border. Chemical analyses show the spiders feed on midges that rely on sulfur-oxidizing microbes, linking the arachnids to a chemoautotrophic food chain. Genetic data indicate these cave populations are diverging from surface relatives, and researchers suggest isolation plus a reliable food source may have promoted the evolution of colonial behavior. The study is reported in Subterranean Biology (Oct. 17, 2025).
07:11, 08.11.2025Science
World’s Largest Spider Web Found in a Sulfur Cave on the Albania–Greece Border
Explorers from the Czech Speleological Society discovered the largest known spider web while surveying a sulfur cave straddling the Albania–Greece border. The extraordinary colonial web — dubbed a “megacity” by researchers — spans more than 1,040 square feet (nearly half a tennis court) and is estimated to contain about 111,000 spiders belonging to the species Tegenaria domestica and Prinerigone vagans. A separate research team documented the find and reported that this is the first recorded instance of these two species building webs together.
Life in an extreme habitat. Sulfur caves are among Earth's most extreme habitats: they are pitch-dark and filled with hydrogen sulfide gas, which is toxic to most organisms. Ecosystems in these caves rely on sulfur-oxidizing microbes whose chemical activity supports a unique, chemoautotrophic food web. That microbial production sustains small aquatic insects and other invertebrates, which in turn feed larger predators.
Who the spiders eat and how they survive. To understand how the spiders persist in this hostile environment, researchers analyzed chemical signatures in spider tissues. The data indicate the arachnids primarily feed on tiny midges that emerge from cave pools; those midges depend on sulfur-oxidizing microbes for nutrition. In other words, the spiders are indirectly sustained by chemoautotrophic microbial communities rather than photosynthesis-driven food chains.
Genetic divergence and new social behavior. Genetic analyses revealed that the cave-dwelling populations of both species are becoming genetically distinct from surface relatives, suggesting adaptation to subterranean life. The researchers propose that prolonged isolation combined with a stable, abundant food supply may have favored the unusual emergence of colonial behavior in species typically considered solitary.
“This discovery shows that nature still holds many surprises for us,” said co-author István Urák of Sapientia Hungarian University of Transylvania, Romania.
Reported in: István Urák et al., “An Extraordinary Colonial Spider Community in Sulfur Cave (Albania/Greece) Sustained by Chemoautotrophy,” Subterranean Biology, No. 53. Published online October 17, 2025 (CC BY 4.0).