In 2005, Tracie Seimon, a biologist and self-professed arachnophobe, was flipping over rocks and looking for frogs high in the Peruvian Andes.

But beneath those rocks, she found something unexpected—and, at the time, a little unsettling: “We started seeing these little burrows with fuzzy little bums sticking out,” says Seimon, then at Columbia University. She convinced a colleague to help her extract and photograph one of the creatures—which turned out to be a two-inch-long tarantula.

Finding a tarantula at that elevation, more than 14,700 feet up, was a revelation. Normally, these hairy spiders aren’t too fond of arid, oxygen-deprived mountain air or subglacial terrain. But little did Seimon know, the South American hills were literally crawling with previously undescribed tiny tarantulas—including