The insect itself is not readily visible. To check for spider mites, hold a piece of white paper under a twig and tap the twig hard. Look carefully at the piece of paper. If tiny specks begin to move, they are most likely spider mites. Anything big enough for you to identify as a spider is not the culprit.
Spider mites feed on the foliage leaving it looking rough and speckled.
They can both damage the looks and the health of the plant. There is a type of aphid that injects its eggs into twigs on spruce. The injection sites then swell up and look a bit like a pineapple or a porcupine. Two types of this aphid exist. The Cooley spruce gall aphid attacks the tip of a shoot and the Eastern spruce gall aphid targets the base of the new shoot.