Typically found in groups, members of the Family Aphididae (aphids) are soft-bodied, range in color from light yellow to dark grey, and may occasionally be winged. While most aphids measure around 2mm in length, the largest known species, Tuberolachnus salignus (the willow aphid), can grow to just under 6mm long. Aphids feed by extracting the sugary liquids from the phloem tissues of suitable plants through a hardened stylet; excess sugars are then excreted in the form of honeydew, a favored treat of ants, wasps, and other insects. Both the feeding process and the excretion of honeydew (by encouraging mold growth) can be destructive to plants, earning Aphididae a rather poor reputation among gardeners.

Aphid sexuality is quite complex, including both asexual reproduction concluding with live birth and sexual reproduction concluding with egg laying. In spring, when hatching occurs, all emerging aphids are female and reproduce asexually, essentially giving birth to three or more clones of themselves every day. As the end of summer approaches, the reproductive strategy of aphids in climates with cold winters shifts and both males and females are produced. After mating, the sexually reproductive females deposit eggs in the protective crevices of plants; safe from harsh winter weather, these eggs hatch the following spring and the cycle begins anew.

Aphids have a number of natural predators, including green lacewings, parasitic wasps, and the ever popular lady beetle. Aphid defenses range from waxy, thread-like shells to the storage and release of harsh chemicals derived from plants on which the aphids feed.