Utah State University Extension
The fall webworm, Hyphantria cunea, is a common defoliator of ornamental and fruit trees in Utah. Starting around late July, the caterpillars, webbing, and damage become noticeable, particularly in some of the canyons adjacent to populated areas (Little Cottonwood canyon, Logan canyon, Provo canyon, etc.).
Davis, Ryan S. and Jones, Vincent P., "Fall Webworm" (2011). All Current Publications. Paper 900.