Caves and mines are home to some of the most unusual species on Earth. From unicorn fish to centipedes, these damp and often isolated environments have conditions that can produce some extraordinary-looking species, including all kinds of arachnids. 

In 2013, a new species of cave-dwelling spider was found in a small mountain range outside of La Paz in Baja California Sur, Mexico. This spider was one heck of a find, measuring roughly the same size as a softball, with the name given as Califorctenus cacachilensis. This newly found specimen is related to the same group as the highly venomous Brazilian wandering spider, according to the paper describing the species.

“The exoskeleton was abnormally big and I could tell by the eye pattern that it was in a group of spiders, wandering spiders from the Family Ctenidae,” said Jim Berrian, field entomologist at the San Diego Natural History Museum and co-author of the study, in a statement.

The team thought that the spider was probably nocturnal, so returned to the cave at night to catch a glimpse of the whopper.

“When I saw these spiders for the first time, I was very impressed by their size,” said spider expert Maria Luisa Jimenez, a researcher at Centro de Investigaciones Biológicas del Noroeste. “In all my experience over the years collecting spiders on the peninsula, I had never seen a spider this large. I suspected that something new was waiting to be described."

Researchers also went a step further than uncovering just one new species of mine spider, when in February 2023, a team found seven new species of troglobitic spiders in a cave in Israel. Different species inhabited different sections of the cave and had differences in their vision based on how much light was available in each niche within the cave. 

Mine spiders could be helpful to humans too. In November 2019, a study was published that indicated that two species of Arctic wolf spiders in Greenland acted as bioindicators of metal contamination in Arctic mine sites, particularly for silver and cadmium. This could help inform policy decisions related to the environmental concerns around heavy metal contaminants and pollution. 

According to a Newsweek article, around 1,000 species of spider are thought to live in caves and mines across the world. From the giant huntsman to the new Brazilian species, and those hiding in Mexican caves, these spiders can do everything from hunting to helping inform policy – and some of them don’t even need eyes to do it.