True to their name, douglas-fir tussock moth caterpillars prefer to feed on douglas fir. Since the eggs hatch in mid-May, they feed on the trees’ new growth and can defoliate trees entirely. While a tree may survive one year of needle defoliation, pretty much all trees will die from two consecutive years of chomping.
Photo by Melissa Verworn on 7/15/20 near Missoula, MT.