Hover flies, aka syrphid flies, are a common sight in the garden. Of the 900 or so species native to the United States, most are mistaken by many gardeners as being a bee or a wasp due to their mimicking coloration pattern of black and yellow stripes on their abdomens. But these stingless imposters are important beneficial insects in the garden that feed on the likes of aphids, thrips, immature leafhoppers, and other small, soft-bodied plant pests. They are one of the first beneficial insects to become active in the spring and get an early start on helping to suppress those early aphid populations on certain ornamentals and vegetables.
Hover flies get their names from their pattern of flying, often hovering in the same spot for 5 to 10 seconds. If you have flowers blooming, you have hover flies visiting. They are a very common sight in the garden. There are several ways to distinguish them from a bee or wasp. Hover flies are in the insect order Diptera, which are the flies. Flies only have one pair of wings, whereas bees and wasps have two pairs. Hover fly heads are almost all eyes with very short (almost unseen) antennae. Bees and wasps have more space between the eyes, which are more to the side of their head, and elbowed antennae that are easily seen.
Hover flies overwinter as either adults or pupae, depending on the species. The ones that overwinter as adults become active anytime daytime temperatures are over 50oF. Winter weeds and early spring blooming plants serve as food for these adults, which feed on pollen and nectar. Adults have good eyesight and, when not feeding, are looking for aphids or other plant pests which will serve as food for the larval stage. Eggs are laid singly on leaves and stems where pests are present. Eggs hatch in 3 to 5 days into a larval stage that, with flies, is called a maggot. It appears headless and is a legless worm-like creature around a quarter of an inch long that slithers about looking for prey. The head end is tapered, and the rear end is larger and rounded. The larvae go through three growth stages or molts over 1 to 3 weeks before pupating to change into the adult stage. The whole life cycle lasts approximately one month, and there may be up to seven generations through the growing season.
The larva can eat over 400 aphids during its development. A healthy population of syrphid flies can reduce aphid populations by as much as 70 to 100%. In combination with other beneficial insects such as ladybeetles, parasitoid wasps, and aphid lions, many of your garden pests can be destroyed.
How do you encourage hover flies and other beneficial insects to take residence in your landscape? Provide a source of food for both the adult and larval stages. Blooming plants that attract other pollinators will attract the adult hover flies as well as other beneficial insects. If you have nothing blooming in early spring, leave a small area of blooming winter weeds in an out-of-the-way place until other flowers are blooming.
To provide food for the larvae, you have to tolerate a population of pests. If you routinely apply insecticides to control pests, you will not have much help from hover flies or any other beneficial insects. Be observant when you see aphid populations and see if you can find the presence of hover fly larvae or some of the other beneficial insects mentioned earlier. If nothing is found, use something like insecticidal soap or just a sharp stream of water to reduce the aphid population without leaving residual insecticides behind that would impact the beneficial insects when they do show up – and they will.
For more information on hover flies and other beneficial insects, visit the Clemson Home and Garden Information Center for this fact sheet, HGIC 2820 Natural Enemies: Predators and Parasitoids which describes many of the beneficial insects that are common in the landscape.