Why do scale insects appear on leaves or branches?

The presence of scale-like insects attached to leaves, branches, or stems usually indicates a scale insect infestation. These small insects remain fixed to the plant, protected by a hard or waxy covering, while feeding on its sap. Severe infestations can weaken the plant, cause yellowing and leaf drop, and encourage the development of sooty mold due to the honeydew produced by some species.