spider mite

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of numerous small red mites of the family Tetranychidae that feed on plants, sometimes causing damage to crops, and often spin webs on leaf surfaces.

from The Century Dictionary.

• noun A parasitic mite or acarid of the family Gamasidæ.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun web-spinning mite that attacks garden plants and fruit trees