Bundles of brown, dead needles tied to the twig are obvious on close examination. High infestations can cause noticeably thin foliage.
Eggs are laid like shingles on the spruce needles. After hatching, the larva enters the base of the needle, hollowing it out. The larvae cut the needles off after completely mining them. Dense mats of silk threads hold the dead needles on the twig. Larvae feed on one needle after another untill fall. At this time, the larvae overwinter inside a needle. They emerge in the spring and feed till they pupate
If necessary, apply an insecticide in early spring.