Researchers found an enormous spider colony inside Sulfur Cave on the Albania–Greece border: a 1,140 sq ft silk web sheltering an estimated 110,000 spiders of two species (Tegenaria domestica and Prinerigone vagans), reported in Subterranean Biology. Scientists attribute peaceful coexistence to an abundant food supply (an estimated 2.4 million midges), permanent darkness, and genetic differences between cave and surface populations. The discovery raises new questions about the evolution of group living in typically solitary spiders.
Giant Cave Web Shelters 110,000 Spiders — Two Species Cohabit in an Unusual Colony
Researchers found an enormous spider colony inside Sulfur Cave on the Albania–Greece border: a 1,140 sq ft silk web sheltering an estimated 110,000 spiders of two species (Tegenaria domestica and Prinerigone vagans), reported in Subterranean Biology. Scientists attribute peaceful coexistence to an abundant food supply (an estimated 2.4 million midges), permanent darkness, and genetic differences between cave and surface populations. The discovery raises new questions about the evolution of group living in typically solitary spiders.
11:14 PM, 11/14/2025Science
Massive silk carpet in Sulfur Cave houses an unexpected multi‑species community
Researchers have documented what may be the world’s largest known spider web: a roughly 1,140-square-foot carpet of silk lining a passage in Sulfur Cave on the Albania–Greece border. The web shelters an estimated 110,000 spiders — about 69,000 of the common house spider Tegenaria domestica and roughly 42,000 Prinerigone vagans — living side by side in funnel-shaped webs.
The discovery, first noticed by Czech speleologists in 2021 and reported in the journal Subterranean Biology last month, surprised scientists not only because of the web’s size but because two normally solitary species appear to coexist peacefully in permanent darkness.
Why don’t they fight?
Investigators suggest several likely reasons: an unusually dense swarm of midges — estimated at about 2.4 million individuals — provides a steady food supply; the cave is humid, sulfur‑rich and largely free of many surface predators; and darkness may impair visual cues that typically provoke aggression. Evolutionary biologist Dr. Lena Grinsted (University of Portsmouth), not part of the study, compared the situation to people sharing an apartment building: communal shared spaces, limited interference inside private living spaces.
“Group living is really rare in spiders,” Dr. Grinsted said. “The fact that there was this massive colony in a place that nobody had really noticed before — I find it extremely exciting.”
Dr. Grinsted and others note that the larger spiders may rely more on vibratory signals than vision to detect prey, reducing mistaken attacks on neighbors. She also considers it unlikely the species cooperate in hunting or brood care beyond contributing silk to the same communal network.
Genetics, ecology and cave life
Co‑author Dr. Blerina Vrenozi (University of Tirana) reported DNA differences between cave and surface populations: genetically distinct groups of the same species appear to have adapted to the subterranean environment. The cave also supports large bat colonies that feed on the same midges — leading one researcher to describe the site as a near-constant party for insectivores.
Field teams caution that population estimates could be slightly inflated because some funnel webs may be abandoned. Still, the density and unusual social behavior provide an exceptional opportunity to study how abundant resources and predator‑free conditions can reshape normally solitary species’ social strategies.
The discovery even prompted a lighthearted border question: the silk carpet lies on the Greek side of the border, according to the expedition leader Marek Audy.
Implications
Experts say the colony raises important evolutionary questions about the conditions that favor group living, how sensory limitations affect social tolerance, and how stable such systems would be if environmental conditions change. Follow‑up studies, including detailed genetic work and long‑term monitoring, could reveal whether this cohabitation is a stable adaptation or a fragile response to an unusually rich microhabitat.