Damage The young nymphs, called sexuparae and progredientes, feed on tender, expanding needles causing them to twist, curl and discolor. Certain trees seem to react more than others. The summer generation attach to the under surface of fully hardened needles and apparently cause little damage other than forming small waxy balls. Though this pest is often called an aphid, it is actually a member of a closely related group, the adelgids. Aphids have a pair of cornicles, tubes on the upper tip of the abdomen, while adelgids do not.
Adelgids also have very short antennae.
The Cooley spruce gall adelgid has four distinct forms which can be found on Douglas-fir during a season. This pest also infests Colorado spruce where it forms a gall. On Douglas-fir, all the forms inhabit the needles and do not form a gall. However, the adelgid can continue generations on Douglas-fir, year after year, without having to go to Colorado spruce. In the spring, March to mid-April, these small dark brown adelgids begin to suck sap and molt into wingless females covered with long, white, waxy threads.