A Cave Spider That Turns Up Everywhere

Caves work like islands for the animals that live in them. Many are troglobionts, species adapted to life underground — over generations, for instance, they lose their sight in the dark. Those adaptations limit how far they can travel, and many cannot leave their cave at all. Populations of one species cut off in separate caves tend to drift apart genetically over time until they become different subspecies.

The exception

The cave spider Phanetta subterranea breaks that pattern. It is found in more caves than any other troglobiont in North America. A team of scientists set out to learn whether its scattered populations had become separate subspecies, as would be expected.

What the DNA showed

The researchers compared the DNA of P. subterranea collected between 1998 and 2023 from 40 caves in seven U.S. states. Spiders from caves as much as 600 kilometers (about 372 miles) apart turned out to have surprisingly low genetic diversity. The team concluded that the species probably has no subspecies.

That answer raises a new question: how did one cave-bound spider come to live in so many caves so far apart? The authors offer some ideas for solving that mystery. Their study appeared in the journal Subterranean Biology in December 2024.

Sources

• National Park Service, Park Science magazine, Volume 39, Number 1, Winter 2024–25 (January 15, 2025), "Research Roundup": "Scientists Solve One Spider Mystery—and Find Another," by the editors, summarizing Kennedy and others, "Remarkably low genetic diversity in the widespread cave spider Phanetta subterranea (Araneae, Linyphiidae)," Subterranean Biology 50: 105–118 (2024). The article's photograph of the spider, credited to Matthew L. Niemiller, is not reproduced.