Massive Spider Colony Reveals Rare Cohabitation

A remarkable discovery in Sulfur Cave on the Albanian-Greek border has revealed what scientists believe to be the world's largest spider web, housing an estimated 110,000 arachnids living in an unprecedented arrangement.

The enormous 1,140-square-foot web stretches along a narrow passage wall deep inside the cave, which extends into Albania from its entrance in Greece. The cave was carved out by the waters of the Sarandaporo River to form the Vromoner Canyon.

What has particularly excited researchers is not just the size of the colony, but the fact that two different spider species are peacefully cohabiting. The colony contains approximately 69,000 Tegenaria domestica (common house spiders) and 42,000 Prinerigone vagans, a smaller species.

This behavior has never been observed before. Typically, the larger house spider would prey on its smaller neighbor, making this peaceful arrangement highly unusual.

Dr. Lena Grinsted, a senior lecturer at the University of Portsmouth, told the Associated Press she was very excited by the study. She explained that group living is really rare in spiders, and finding this massive colony that nobody had really noticed before was extremely exciting.

Scientists believe several factors contribute to this unusual cohabitation. The cave environment provides an estimated 2.4 million midge flies, creating an unusually dense swarm that offers a constant food source. When food is abundant, spiders become less aggressive toward each other.

The cave's permanently dark zone, located about 50 meters from the entrance, may also play a role. However, Dr. Grinsted suggests it is more likely that the larger spiders have evolved to respond to vibratory cues when small flies land on their webs, rather than attacking anything that moves.

She compared the spider arrangement to humans living in apartment blocks, where people happily share stairs and lifts but become aggressive if uninvited guests enter their living rooms.

The research team, led by Czech speleologist Marek Audy, first observed the giant web in 2021. They published their findings last month in the journal Subterranean Biology.

DNA analysis revealed that the spiders living inside the cave have different DNA from the same species living outside, suggesting they have adapted to the unique cave environment. Interestingly, cave spiders lay about one-third fewer eggs compared to outdoor spiders, likely because survival rates are higher in this protected environment.

Dr. Sara Goodacre, a professor at the University of Nottingham, noted that the benefits of being part of this community far outweigh the costs, though she warned that if environmental conditions change, the cooperative arrangement could break down.