This is the primary pest of Norway spruce. The Cooley spruce gall adelgid is indigenous to North America. This adelgid usually affects Colorado blue, Sitka, Englemann, and Oriental spruces. The galls shape, size, and position on the twig aid in identifying the species involved. Galls interfere with the natural formation of twigs and cause curling, stunting and the eventual death of new growth.
Heavy infestations give the trees a ragged appearance and destroy their beauty.
Some trees have a natural resistance or immunity to these adelgids, and in spite of the presence of the insects, the galls never completely develop or may not form at all. New galls, formed in early summer, are green with purple or reddish, curved markings. Old galls are reddish-brown and have several small, open cavities. Terminal buds are not destroyed until the entire twig dies. Terminal buds are injured quickly.