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. These adelgids frequently migrate to Douglas fir, an alternate host, but do not produce galls on this tree. Immatures, called nymphs, winter beneath a thread-like cover of waxy material, usually near the base of a terminal bud. The nymphs begin feeding in early spring and, when mature, lay eggs on the bases of expanding buds and feed on developing needles.