This article was originally published in bioGraphic. One dusky June evening, two days before the 2022 Pennsylvania Firefly Festival, the biologist Sarah Lower sat on a back porch, watching the sky for a specific gradation of twilight. A group of Lower’s students from Bucknell University hung around her, armed with butterfly nets and stopwatches for counting the time between firefly flashes—a way to differentiate between the multiple lightning-bug species that live here at the edge of Pennsylvania’s Allegheny National Forest. This postindustrial expanse of second-growth trees and hills pimpled with oil wells also happens to rank among the world’s best places to see fireflies. Once the cloudy sky blushed red from its last glimpse of the setting sun, I set out with Lower and her students toward the forest edge. Moving from habitat to habitat as the evening deepened, Lower narrated which species we saw and their different behaviors. Her students, meanwhile, netted their way down a wish list of research samples. First up was Photinus macdermotti, a firefly species that emits two quick flashes. …