CAVE CITY, Ky. (AP) — Kurt Helf crawled through Mammoth Cave National Park, holding a humidity-measuring device in one hand and a camera in the other. He leaned in awkward positions parallel to limestone curvatures, joking that "yoga is coming in handy" as he laid on his back to photograph long-legged, spideresque critters.

For the past five years, Helf, an ecologist with the National Park Service, has led an effort with the Cumberland Piedmont Network to monitor more than 100 species of crickets living inside Mammoth Cave.

"Crickets are the most numerous species in caves, and most are secreti...