World’s Largest Spiderweb with 111,000 Arachnids Found in a European Cave

**kellyhound** · #1 ● 11-07-2025, 05:07 AM

Researchers have documented what is believed to be the world’s largest spiderweb inside Sulfur Cave on the Albanian-Greek border.

The massive web is home to an estimated over 111,000 spiders, all living within a patchwork of thousands of individual, funnel-shaped webs.

Stretching across the wall of a dark, narrow passage near the entrance, the web measures 106 square meters (1,140 square feet).

The colony consists of two common species: 69,000 individuals of Tegenaria domestica (barn funnel weavers/domestic house spiders) and over 42,000 Prinerigone vagans.

According to researchers from the Sapientia Hungarian University of Transylvania in Romania, this is the first documented case of these two widespread spider species exhibiting colonial behavior.

Sulfur Cave was formed by sulfuric acid resulting from the oxidation of hydrogen sulfide in groundwater.

Live Science reported that the giant web was first discovered in 2022 by cavers from the Czech Speleological Society during an expedition in the Vromoner Canyon.

After this, a team of scientists visited the cave in 2024 to collect specimens for analysis by lead author István Urák, who later conducted his own expedition to Sulfur Cave.

Fresh DNA analysis confirmed the presence of two spider species that dominate the web.

Interestingly, the spider colony features species not previously known to exhibit this behavior.

Researchers wrote in the study paper that it represents the “first documented case of colonial web formation in these species.”

The two species are common near human homes. However, the cohabitation and cooperation of these two species within a single, enormous web and in such high density is considered a unique phenomenon.

It is typically expected that the barn funnel weavers (T. domestica) prey on the P. vagans.

The study suggests that the lack of light in the cave may impair the spiders’ vision, potentially disrupting their normal predatory instincts and allowing them to coexist.

A unique, sulfur-driven food web sustains the massive spider colony within the cave.

The spiders’ primary diet consists of non-biting midges. These midges, in turn, feed on white microbial biofilms, which are slimy secretions produced by sulfur-oxidizing bacteria living in the cave environment.

A sulfur-rich stream, sourced by natural springs flowing through Sulfur Cave, sustains this entire ecosystem.

It fills the cavern with hydrogen sulfide, a key ingredient that allows the microbes, the midges, and ultimately their spider predators to thrive in this pitch-black environment.

Moreover, the unique, sulfur-rich diet of cave spiders has led to distinct biological changes, as indicated by molecular and gut content analyses.

Their diet causes the cave spiders’ microbiomes to be less diverse compared to spiders of the same two species living outside the cave.

Additionally, molecular data reveal that the cave-dwelling spiders are genetically different from their outside relatives, strongly suggesting they have adapted to their perpetually dark, sulfurous environment.

Researchers are currently working on a follow-up study to gather more information about the unique inhabitants of Sulfur Cave.