Whiteflies are not true flies. They're more closely related to scales, mealybugs, and aphids. These pests are more commonly associated with plants growing in greenhouses than those growing in homes.
Adult whiteflies are small insects, approximately 1/16th inch (1.5 mm) in length, with four powdery white wings. When heavily infested plants are disturbed, one may notice a "cloud" of tiny white insects rising above it. The immature stages (eggs, crawlers, scales and pupae) are all yellowish and found primarily on the undersides of leaves.
All stages of whiteflies feed on plant sap, using their piercing-sucking mouthparts. Infested leaves can yellow and drop, reducing plant vigor, but usually not killing the plant.
Thoroughly spray all plants brought home from a greenhouse or garden center with insecticidal soap or horticultural oil to kill whitefly nymphs and eggs. Natural enemies include lacewing larvae and parasitoid wasps.