Spider Mites

By Joe Merkelbach (January 2007)

Spider mites are pests with a serious reputation as harmful to many varieties of plant life. In fact, there is opinion that they are the single most harmful plant pest.

Spider mites are actually not insects, but more closely related to spiders, as indicated by their eight legs and ability to weave small webs. There are many species, but the one that seems most notable in relation to houseplants is the two-spotted spider mite, Tetranchus urticae.

The mites damage plants by using their piercing mouth parts to open plant cells and suck out the liquids. If this behavior is concentrated, the plant surface can be discolored and dessicated. Leaves, if present, can be lost.

All spider mites are very small. Two-spotted mites are almost transparent. Their spots develop as waste accumulates on the sides of their bodies. They prefer hot or warm conditions. Moving air around plants is a good preventative measure.

Stopping mite infestations by early detection is an important means of control. Tapping a suspect plant above a white sheet of paper can dislodge the tiny creatures and reveal them – use a hand lens to see them more clearly. If 10 or more mites appear, control should be undertaken.

Spray washing infested plants is a good first technique. Suspect plants should also be quarantined during subsequent treatments.

There are two varieties of pesticides for mites. “Soft” ones like soaps and oils can be used to suffocate the pests. Hard pesticides called miticides are designed specifically to kill mites and their eggs, but they are also quite toxic to people and should be used with care.

The best technique for stopping mites and the havoc they cause in plant collections is vigilance. Watch for discolorations and webbing, and follow steps for controlling the pests.