Czech cavers’ discovery confirmed as the world’s largest spider web
Czech cavers discovered what may be the world’s largest spider web in a cave on the Albania–Greece border, home to over 100,000 spiders. The find was made in 2022, but an international team of scientists has now confirmed its significance: it is the largest spider web ever recorded, and the first known case of two normally solitary species working together.
The discovery took place during an expedition by the Czech Speleological Society to the Vromoner Canyon. While mapping the Sulphur Cave — a cavern formed over time by sulphuric acid produced through chemical reactions in the groundwater — the team came across something they had never seen before, says explorer Richard Bouda:
“The spider web is located in a rather interesting place. If you were to walk through the cave, it’s like entering a huge chamber that suddenly narrows — you have to crawl through a tight, low passage. Then you stand up, and right in front of you, this enormous spider web appears.
“And when you get closer, you can see the spiders living there, moving about, perfectly at home. Even though I wouldn’t say I’m afraid of spiders — I’m fairly used to them — in that place, it really does feel a bit eerie.”
The web isn’t the typical geometric pattern people imagine when they think of a spider web. It’s a dense, sponge-like structure covering more than one hundred square meters — nearly half the size of a tennis court.
An international study, published in October in the scientific journal Subterranean Biology, found that this vast web is home to about 111,000 spiders from two species: Tegenaria domestica, known as the barn funnel weaver, and Prinerigone vagans, also called the dwarf spider. This marks the first documented case of these two common species weaving webs together.
Sulphur Cave itself is an extreme environment — completely dark, hot, humid, and filled with hydrogen sulphide gas, which is toxic to most life-forms. Life inside depends on sulphur-eating microbes that form the base of a simple food chain: tiny flies feed on the bacteria, and the spiders feed on the flies.
Richard Bouda says moving inside the cave was not exactly a pleasant experience, even for seasoned cavers:
“The temperature inside the cave is around 27 degrees Celsius and has a strong sulphur smell. You move through areas where thousands of tiny flies and mosquitoes are buzzing around you, living in the warm air near the ground. We even managed to find some scorpions there, so the biodiversity is quite high — but for some people, it might not be the most pleasant environment.”
Researchers also discovered that the spiders living inside the cave are genetically different from those outside it — suggesting they’ve become isolated and perfectly adapted to life underground. This genetic split, along with their unusual diet, may explain how these normally solitary spiders came to live together over thousands of years.
