Deep within Sulfur Cave, straddling the Albanian-Greek border, lies a sight unlike any other: the world’s largest known spider web. This vast structure sprawls across roughly 1,140 square feet — equivalent to a small house — suspended in a narrow passageway within this labyrinthine limestone cavern sculpted by the Sarantaporos River. But the sheer size of this silk metropolis is only part of the story.
What truly astonished scientists was the delicate ecosystem thriving within it. This wasn’t just an enormous web; it was a teeming spider city. Researchers found 69,000 Tegenaria domestica — commonly known as barn funnel weavers — coexisting with approximately 42,000 Prinerigone vagans, typically encountered in damp habitats. The former species is known to prey on the latter, which are smaller.
“In the cave’s darkness,” Dr. Blerina Vrenozi, a biologist and ecologist at the University of Tirana, explained, “our hypothesis was that they don’t see each other, so there’s no predation.” This peaceful coexistence within the web offers a fascinating glimpse into how limited visibility can drastically alter natural predator-prey dynamics.
Dr. Vrenozi, who specializes in spiders and led this research team, described reaching Sulfur Cave as “pure adrenaline for biologists.” The journey itself was an arduous one, involving waders and ropes to navigate chest-high water currents within the cave’s passages.
“When I shined a light into the cave,” she recalled, “it looked sparkling,” Dr. Vrenozi explained. The massive web wasn’t a single continuous structure but rather thousands of individual funnel-shaped webs woven together, shimmering under her light with an almost ethereal glow.
This unusual subterranean haven owes its existence to several factors. The cave itself is sculpted by sulfuric acid generated from the oxidation of hydrogen sulfide within groundwater. Discovered in 2022 by the Czech Speleological Society, it boasts a constant temperature of around 80 degrees Fahrenheit and offers an abundance of food: over 2.4 million midges attracted to the cave’s damp interior — ample sustenance for this spider metropolis.
The harsh environment also acts as a natural barrier to most other creatures. The air within Sulfur Cave is thick with putrid-smelling hydrogen sulfide, making it uninhabitable for most animals. Even researchers entering the cave require masks to tolerate the “smell of spoiled eggs,” as Dr. Vrenozi vividly described it.
While the exact age of this spider city remains unknown, its remote location suggests it could persist indefinitely. The constant replenishment of food and protection from external threats likely contribute to this longevity.
“Part of the web falls down because it’s too heavy,” explained Dr. Vrenozi, “but it’s a cycle which repeats time after time.” The researchers even noted genetic differences between these cave-dwelling spiders and their surface relatives, highlighting how they have uniquely adapted to thrive in this unusual environment.
This extraordinary discovery provides not only an opportunity to study the evolutionary adaptations of both spider species but also offers valuable insights into how ecological relationships can shift dramatically under extreme conditions like those found within a remote cave system.
