Spiders tend to be solitary creatures, so imagine researchers' surprise when they found more than 100,000 arachnids sharing what is thought to be the largest web on record.
The web is a jaw-dropping 1,140 square feet (106 square meters) and is located in Sulfur Cave on the Albania-Greece border. According to scientists writing in the journal Subterranean Biology, it is the first reported incident of cave spiders building webs together.
Upon further investigation, the team determined the colony's composition. According to their estimates, it is made up of 69,000 Tegenaria domestica (also known as the barn funnel weaver or the domestic house spider) and over 42,000 Prinerigone vagans (a type of sheet weaver).
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Largest Spider Web in Sulfur Cave
The web was first discovered in 2022 by cavers from the Czech Speleological Society. It exists in a permanently dark zone in a narrow passageway approximately 164 feet (50 meters) from the cave’s entrance.
As its name implies, Sulfur Cave contains high concentrations of sulfur gas. This is due to a sulfidic stream that runs from the depths of the cave to its entrance. The result is an extremely harsh living environment that nonetheless supports an entire ecosystem of creatures adapted to it. In the study, the researchers noted the presence of worms, beetles, scorpions, "occasionally some fish,” and, of course, spiders.
Spiders are Unlikely Roommates
Spiders in Sulfur Cave
(Image Credit: Jean-François Flo)
Using DNA analysis, the team discovered that T. domestica and P. vagans were the two dominant species. While T. domestic was responsible for weaving the web, the smaller P. vagans took on the role of squatter. This was surprising because neither species is known for communal living or gregarious behavior, according to the study. T. domestica is a cosmopolitan spider, often found living in buildings and near human settlements, while the British Arachnological Society states P. vagans inhabit wet environments, such as grassy meadows and salt marshes.
What perhaps makes the living situation of these eight-legged housemates even weirder is the fact that T. domestica would be expected to prey on P. vagans. The researchers suggest it may be the cave itself — specifically the lack of light — that enables these two species to peacefully cohabit.
Simply put, the more aggressive T. domestica cannot see their neighbours and might not even know they are there. Instead of turning on each other, the researchers suspect the spiders feast on a diet of non-biting midges that live off microbial biofilms produced by sulfur-oxidizing bacteria.
Additional analysis revealed that high sulfur intake in the diet has impacted the spiders’ microbiomes, decreasing gut bacterial diversity compared to spiders of the same species living outside the cave.
Counting the Sulfer Cave Spiders
On inspection, the researchers discovered the web was essentially a patchwork of thousands of individual funnel-shaped webs joined together. The team then calculated the density of T. domestica living in the colony by counting the number of funnel-shaped webs in 30 6 x 6-inch (15 x 15 centimeter) quadrants and applying those calculations to the whole structure.
The density of P. vagans was estimated by counting individuals in 6 x 4-inch (15 x 10 centimeter) quadrants.
The researchers warned, “The methodology used to estimate spider density may lead to an overestimation due to the presence of abandoned funnel webs that are difficult to distinguish from those in use.”
Even if it is an overestimation, Sulfur Cave may be one for the arachnophobes to avoid.
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from the recent study published in the journal Subterranean Biology: An extraordinary colonial spider community in Sulfur Cave (Albania/Greece) sustained by chemoautotroph
- This article references information from the British Arachnological Society: Summary for Prinerigone vagans (Araneae)
