The spruce spider mite (Oligonychus ununguis) is quite small; about the size of a pollen grain. Symptoms include bronzing and yellowing of needles and may show up later than damage actually occurs. To test for an infestation, tap a branch while suspending a white sheet of paper underneath. Specks that move are probably spider mites. Most active during the spring (March – mid-June) and fall (September – October), these cool-season mites spend the summer as eggs.  Control can be difficult becuase mites are more closely related to spiders than insects.  In addition, the density of the plant offer protection from insecticides.  The oldest and possibly best form of control is by spraying the plant a few times per week with a very sharp spray of water.  Enough force will usually knock the mites off the plant, thus discouraging them from feeding on the particular plant.