The pest is barely visible without the aid of a magnifier and is rarely noticed until discoloured foliage is found on an affected tree.

To check for the presence of mites, sharply jar suspected foliage over a piece of white paper, and watch for movement of tiny objects.

If a red stain appears when the objects are smeared against the paper, the probability is high that spider mites are present.

Spruce spider mites suck sap from needles and shoots, causing the foliage to become mottled.

The fine silk webbing that they spin as they move about the needles catches dust and further impairs the appearance of the host tree.