From left, zookeeper Kelsey Stone, animal wellbeing coordinator and the head of firefly husbandry research, Maloney Dodson and entomology tech Alex Han, all with the Butterfly Pavilion, asses the sex of fireflies caught on Wednesday, June 10, 2026, at Riverbend Ponds Natural Area in Fort Collins, Colorado. (Timothy Hurst/The Denver Post/TNS) FORT COLLINS, Colo. - As the last of the sunset's pink hues disappeared from the sky, the Fort Collins field came to life. One flash appeared. Then another.