Baseball-sized spider discovered in Baja California mine

Researchers at the San Diego Natural History museum recently discovered a new species and genus of spider in the hills of Baja California, called Califorctenus cacahilensis. Researchers at the San Diego Natural History museum recently discovered a new species and genus of spider in the hills of Baja California, called Califorctenus cacahilensis. Photo: San Diego Natural History Museum Photo: San Diego Natural History Museum Image 1 of / 9 Caption Close Baseball-sized spider discovered in Baja California mine 1 / 9 Back to Gallery

While traipsing through the a mine in the hills of Baja California, Michael Wall and Jim Berrian struck gold. Skittering across the abandoned mine shaft was a beast that would send most people running.

The entomologists instead ran toward the creature – a whopping spider the size of a baseball – and captured it for analysis. With juicy fangs, a hairy yellow abdomen and legs for miles, the arachnid was certainly a looker, but neither of the scientists could classify it.

Back in their lab at the San Diego Natural History Museum, the researchers had a eureka moment. Upon corroborating with Mexican entomologist and southern spider expert Maria Jimenez, the scientists confirmed that they had discovered a new species and genus. They named it Califorctenus cacahilensis, after the Sierra Cacahilas mountain ranges where it was first found.

"Discovering a species in entomology and arachnology is not terribly unusual," said Berrian, who published the findings in Zootaxa last month. "There might be another 2-2.5 million species of undiscovered insects and spiders."

Finding such a large spider in a place once roamed by humans, however, is a scientific triumph of sorts.

"It probably shows that there aren't enough entomologists and arachnologists looking for this stuff," Berrian mused.

Generally when dealing with spiders the size of saucers the natural follow-up question is: But are they poisonous?

Berrian is quick to point out that "there's no such thing as poisonous spiders, only venomous spiders." Poison is ingested and venom injected.

Alas, the spider is indeed venomous, but it generally only flexes its fangs for digesting food. Most spiders are skittish, and their first line of defense is flight not fight.

Berrian, who has been working with spiders for over 20 years, admits that the cave spider is the first arachnid to ever bite him. He recovered quickly – "It felt like getting poked by a cactus spine."

Read Michelle Robertson’s latest stories and send her news tips at mrobertson@sfchronicle.com.