Adult hover flies are generally brightly colored-with black-and-yellow abdominal bands-and closely resemble bees or wasps. They’re typically ½- to ¾-inch long and have two wings. Their larvae, which can reach ½-inch in length, are sluglike, tapered toward the head, and generally marked with a yellow longitudinal stripe on the back. Tell-tale black, oily smears of excrement on plant foliage reveal their presence.
Hover flies lay their whitish to gray oblong eggs singly on their sides near or within aphid colonies. They can have many generations per year.
Nonbiting, nonstinging adult hover flies feed on pollen, nectar, and honeydew from aphids and scale insects. Their larvae consume aphids and other small, soft-bodied insects, including thrips and small caterpillars. A single larva can eat hundreds of aphids in a month. Hover fly larvae can detect low numbers of aphids and are particularly useful early in the season.