Scale insect, any of various small insects of the order Homoptera (especially family Coccidae) with a flattened body covered by a layer, or “scale,” of waxy secretion. There are more than 2,000 species. They live on plants, and many are serious pests. The cottony cushion scale did immense damage to the Californian orange plantations after its introduction from Australasia. The elm scale kills trees. Other scale insects are collected for their secretions. The dye cochineal is obtained from a scale insect, and the lac insect used to be collected by the millions—its “scale” turned into shellac.