The balsam woolly adelgid is killing subalpine fir trees in lower elevation forests across the Wasatch Mountains. New research tracks how climate change could expand their habitat. Adults measure a mere millimeter long, and their name comes from the white, woolly-waxy shells they produce to protect the hundreds of amber colored eggs they lay. That fuzz is their most obvious tell, other than the destruction they leave behind. Balsam woolly adelgids are now in Utah, and they are spreading. New research from the University of Utah maps their current habitat and the severity of the insects’ damage. It also offers a warning: Climate change and the subsequent warming of the mountains could cause these tiny harbingers of tree sickness and death to thrive.