Giant, Odorous, Spongy Web Found in Balkan Cave Shows Unprecedented Spider Cooperation

Deep beneath the rugged mountains of the Balkans, in a pitch‑black limestone cavern that has remained untouched for millennia, scientists have uncovered a startling natural marvel: a massive, foul‑smelling, sponge‑like web that appears to be the joint handiwork of two spider species that normally regard each other as rivals.The discovery was made last month by a team of arachnologists from the University of Zagreb, who were conducting a routine biodiversity survey in the Šar‑Kamen cave system, a remote network of tunnels known for its extreme humidity and near‑total darkness. While navigating a narrow passageway, the researchers stumbled upon a sprawling silken structure that stretched across the cavern floor and clung to the jagged walls, covering an area of roughly eight square meters.“What we saw was unlike any spider silk we’ve ever encountered,” said Dr. Ana Petrović, lead author of the forthcoming study. “The web was thick and spongy, almost like a living mattress, and it emitted a strong, unpleasant odor that seemed to repel other insects. Its sheer size and the way it was woven suggested the involvement of more than one spider species.”Subsequent analysis identified the culprits as the European garden spider (*Araneus diadematus*) and the lesser European spider (*Zodarion germanicum*). The garden spider is a classic orb‑weaver that constructs intricate, circular webs to capture flying prey, while the *Zodarion* is a nocturnal ant‑specialist that typically lives solitary, ground‑dwelling lives and rarely builds extensive webs.Genetic testing of silk samples confirmed that both species contributed to the structure. The garden spider’s silk formed the outer, more elastic layers, whereas the *Zodarion* added a denser, more absorbent inner matrix that gave the web its characteristic sponginess. The combined material appears to serve multiple functions: it traps a wide variety of insects, retains moisture in the arid cave environment, and the pungent scent—produced by a blend of volatile compounds unique to each species—acts as a deterrent against potential predators and competing arthropods.The collaboration is especially surprising because field observations over the past decade have documented fierce territorial disputes between these two spiders when they share overlapping habitats. Dr. Petrović believes that the extreme conditions of the cave—constant darkness, limited food sources, and high humidity—may have driven the two species to set aside their antagonism in favor of mutual survival.“This is a remarkable example of ecological flexibility,” she explained. “When resources are scarce, even species with a history of competition can evolve cooperative strategies. The web functions like a shared pantry and a communal shelter, increasing the odds that both spiders can thrive in an otherwise hostile environment.”The researchers also noted that the web’s odor, while unpleasant to human noses, appears to have antimicrobial properties, possibly protecting the spiders from fungal infections common in damp caves. Laboratory tests are underway to isolate the chemicals responsible, with potential applications in medicine and industry.Local conservationists are already concerned about the delicate balance that allows such a phenomenon to exist. The Šar‑Kamen cave is a protected area, but increasing tourism and illegal collection of cave fauna could threaten the fragile ecosystem that supports this unique partnership.“This find underscores how much we still have to learn about subterranean biodiversity,” said Dr. Marko Lukić, a speleobiology expert not involved in the study. “Every new observation like this reminds us that caves are reservoirs of evolutionary experiments that could vanish before we fully understand them.”The full findings are slated for publication in the upcoming issue of *Journal of Arachnology*, where the authors will detail the web’s architecture, chemical composition, and the behavioral observations that led them to conclude a cooperative relationship between the two spider species.