Woolly aphids (subfamily: Eriosomatinae) are sap-sucking insects that produce a filamentous waxy white covering which resembles cotton or wool. The adults are winged and move to new locations where they lay egg masses. The nymphs often form large cottony masses on twigs, for protection from predators.

Woolly aphids occur throughout the Northern Hemisphere. Many of the numerous species of woolly aphids have only one host plant species, or alternating generations on two specific hosts. They have been known to cause botanical damage and are often considered a pest. While most damage is minor, they can spread plant diseases and fungi. Some species can produce galls as well.

In flight they have been described as looking like "flying mice." Other nicknames include "angel flies", “cotton fairies”, "fluff bugs", "fairy flies", "ash bugs", "snow bugs", "fluffer fairies", "poodle flies", and "fluffy gnats".