Only females of this adelgid are known to occur. The adelgids mature about early May and produce a conspicuous, waxy cover under which they lay their eggs. The eggs hatch in about a week, and the young insects begin to feed on the buds that had been fed upon by the overwintering forms. Continued feeding induces abnormal growth of plant cells and progressive enlargement of the bases of infected needles. Eventually, the enlarging needles coalesce and form the characteristic pineapple-shaped gall within which the insect lives and grows.
Galls protect the adelgid from most insecticide sprays.
The adelgids and galls mature in midsummer. The galls split and the mature adelgids emerge, develop wings, fly to the needles of the same or some other sruce and lay eggs at the base of the new growth. The eggs soon hatch and the immature forms that emerge will feed until the onset of cold weather, overwinter at the needle bases and then resume their life cycle the following spring. The Cooley spruce gall adelgid is a native insect most commonly infesting blue spruce but also found on Stika and Englemann spruce as well as Douglas fir. Only females of this species are known.