Scale is a little insect that damages warm climate plants and house plants. It’s a strange little pest since the adult form settles into immobility on stems and leaves and looks like anything but an insect. The waxy blobs that cover the adult scale harbor nasty little sucking critters that drink out the life fluids from the plant. Immature scale is mobile and very tiny. Males are also small and have wings, but they do not feed or harm plants. The adult females, like aphids, sometimes excrete a sweet, sticky honey-like liquid that can drip onto surfaces below. The liquid can also attract ants.
Soft scale and armored scale are common in warm environments. They are killed off by frosts of varying degrees, but then so are many of their host plants. The mealybug is a type of scale, too. There are hundreds of types of scale insects. They come in a wide variety of shapes, textures, favorite host plants and climate tolerances.
Scale can be a serious pest to edible crops like citrus and debilitating to houseplants. There are some varieties that are used commercially to make shellac finishes and cochineal dye is a red pigment that has been harvested from some species of scale insects. But the scale insect is far better known for its destructive effects on plants.
Scale is difficult to control and natural preditors are the most effective. For individual houseplants and in the home garden, horticultural oils can be effective by literally smothering the insect. Some insecticides can kill the mobile young and the males on contact, but rarely penetrate the adult female waxy shell.