scale insect

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

• noun Any of various small plant-feeding insects of the superfamily Coccoidea that secrete a waxy substance covering the body and are often agricultural pests.

from The Century Dictionary.

• noun Any insect of the homopterous family Coccidæ; a scale: so called from the appearance they present when sticking fast to plants, and from the fact that most of the common forms secrete a large shield-like scale under which they hide and feed.

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

• noun small homopterous insect that usually lives and feeds on plants and secretes a protective waxy covering