The emerald ash borer is on the most-wanted list in Ulster County, New York. This jewel-green beetle’s appetite for the inner bark of ash trees has proven deadly for forests and cityscapes, leaving ash trees by the millions ravaged. In this video, TIME meets Foresters Jeff Rider and Michael Cullen, who are working to discover the habits and natural enemies of this beetle. The foresters are also fielding calls from residents like Valerie McCloskey, whose ash trees have been infested and are about to fall. Area residents are advised not to transport firewood, in hopes that a quarantine might slow the spread of the pest. But the threat is immense, and ash borers continue to take down some of the continent’s most handsome trees.