World's largest-known spider web discovered in Sulfur Cave
Researchers have documented what appears to be the world's largest-known spider web: a dense, carpet-like expanse of funnel webs covering roughly 1,140 square feet along a passage wall inside Sulfur Cave. The cave entrance lies in Greece and its passages extend into Albania, and the web was found about 160 feet from the entrance in a permanently dark, sulfur-rich zone carved by the Sarandaporo River through Vromoner Canyon.
Two species, one enormous colony
The colony is estimated to contain about 110,000 spiders made up of two distinct species living side by side: roughly 69,000 Tegenaria domestica (common house spiders) and about 42,000 Prinerigone vagans. The research, published in the journal Subterranean Biology, drew attention not only for the web's scale but for the unusual coexistence of two species that would ordinarily compete or predate on one another.
Why they can coexist
Scientists point to an abundant and stable food source as a likely key to the colony's success. The authors estimate an unusually dense swarm of about 2.4 million midges (chironomid flies) that fill the air near a sulfidic stream inside the cave, providing a continuous supply of prey. The dark environment and the spiders' reliance on vibratory cues rather than vision may also reduce aggressive encounters between species.
Evolutionary biologist Lena Grinsted of the University of Portsmouth said she was "very excited" by the find because group living is rare in spiders and the colony resembles 'humans sharing an apartment block' in how individuals tolerate proximity while guarding their own space.
Fieldwork and findings
The giant web was first observed in 2021 by a team of Czech speleologists led by Marek Audy. In 2022 the team expanded to include scientists from several universities, and their combined work produced the recent paper. Co-author Blerina Vrenozi of the University of Tirana noted that DNA analyses indicate the cave populations are genetically distinct from the same species that live outside the cave, suggesting local adaptation to the subterranean environment.
Marek Audy described the structure as 'dense, more like a blanket' that offers effective refuge: female spiders retreat into the silk when threatened and are difficult for predators to extract. The researchers also observed that cave spiders lay about one-third as many eggs as outdoor spiders, likely because protected conditions increase offspring survival.
Ecological context and cave fauna
Besides spiders and midges, the cave hosts other terrestrial fauna including centipedes, terrestrial isopods, scorpions and beetles, and it supports large bat colonies that feed on the abundant midges. The sulfidic, humid conditions create a productive subterranean ecosystem despite permanent darkness.
Methodological notes and implications
The authors caution their counting methods may slightly overestimate the colony size because some funnel webs might be abandoned or unoccupied. Still, external experts say the discovery offers rare and valuable insight into social and evolutionary dynamics in spiders and other organisms adapting to extreme or resource-rich habitats.
Sara Goodacre of the University of Nottingham commented that such studies help reveal the strategies natural selection favors, adding that communal living may be advantageous in this stable, food-rich environment, though social systems could break down if conditions change.
Beyond scientific interest, the find stirred local curiosity about jurisdiction: investigators report the sprawling web lies on the Greek side of the border. The discovery underscores how much remains to be learned about subterranean biodiversity and the surprising social strategies of animals long thought to live mostly solitary lives.
