Deep underground in a dark, sulfuric cave on the border between Albania and Greece, scientists have made an incredible discovery – a giant communal spider web spanning more than 100 square meters (1,000 sq ft), dense enough to resemble a living curtain, home to an estimated 110,000 spiders.

An international team of European researchers, including scientists from the Czech Speleological Society, came across it while undertaking a wildlife survey in 2022, and were not just taken aback by the size of the multilayered web but what it housed: around 69,000 Tegenaria domestica and 42,000 Prinerigone vagans spiders living side by side in this massive silk structure with an estimated surface area of 106 sq m (1,141 sq ft)

It’s the first time either species has ever been seen living cooperatively, and the first recorded instance of colonial web-building in what’s known as a chemoautotrophic cave.

This cavern, known as Sulfur Cave, houses a chemoautotrophic ecosystem sustained not by sunlight but chemosynthesis – or the process of converting chemical energy into organic matter. Here, sulfur-oxidizing bacteria grow in thick white biofilms on wet rock and sediment. These microbes are then eaten by small invertebrates such as midge larvae and isopods, which are in turn preyed on by larger insects like spiders, beetles, and centipedes. The entire ecosystem is self-contained and independent of external input, running on the energy released when bacteria convert toxic hydrogen sulfide into sulfate.

This remarkable life support system is all thanks to a warm toxic stream that runs through it, with its water a constant temperature of about 26 °C (79 °F) and loaded with dissolved hydrogen sulfide – which gives it its distinctive rotten-egg odor.

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