The mites have a similar appearance to those already discussed. Coloration varies from green to deep olive to brownish red. Close inspection of the needles will reveal tiny white flecks and speckles where the mites have fed. Prolonged feeding causes yellowing, browning, and premature needle drop, often originating from the canopy interior. Infested foliage may also display webbing, eggs and cast skins.
Heavy attacks can cause branch dieback or death of the plant.
The spruce spider mite is known as a cool season mite and is most active in early spring and late fall. It overwinters in the egg stage attached to the base of needles or on the bark. The eggs hatch in early spring, and mature in 2 to 4 weeks. Damaging populations may be reached in April and May, before warm summer temperatures slow their activity. Spruce spider mite populations rebound in the fall with the return of cooler weather, and feeding may continue into December or beyond, if winter temperatures remain mild.