Mealybugs (Family Pseudococcidae) are sexually dimorphic scale insects found on plants. I observed several large female mealybugs on these still unidentified weeds in Sabino Canyon last September.
The flightless female mealybugs feed on plant sap and are covered in protective, white, waxy, mealy secretions that make them look like they were rolled in flour. The short-lived adult males can fly but not eat, and their sole purpose is to fertilize the sedentary females.
Female and young mealybugs suck plant juices and can congregate in large numbers, making them potentially serious plant pests. Their protective waxy secretions can cover much of the colony, making them difficult to control once established.
Mealybugs are a danger to plants but not to other insects. However, not everything that looks like a mealybug truly is one. False mealybugs, larvae of lady beetles in the genus Scymnus, look deceptively like them, but these larvae are actually beneficial predators that feed on small, plant-feeding insects. One way to tell a mealybug and a Scymnus larva apart is to look for the mealybug's characteristic white, waxy secretions, not only on her back, but also deposited on the adjacent plant as well.