Hover or Flower Flies
Hover or flower flies are common and important natural enemies of aphids and
other small, slow-moving insects. The adults resemble bees or wasps, and are
often seen visiting flowers, hovering over the flowers and darting around.
There are many different species that range in size from less than ¼ inch long to more than ¾ inch long. Many have the typical black and yellow stripes on the abdomen that give them a bee-like appearance. Other species are hairy with a long, thin abdomen. All have large eyes and short antennae without an elbow unlike the bees they resemble.
Adult hover flies need flowers as nectar and pollen sources. They are attracted to weedy borders or mixed garden plantings that are also infested with aphids. They can be especially common in old fields with many weedy plants. Some flowers that are especially attractive to hover flies include wild carrot or Queen Anne's lace, wild mustard, sweet alyssum, coriander, dill, and other small-flowered herbs.
Female hover flies lay tiny white eggs singly on leaves or shoots near or among aphid colonies. Each female may deposit several hundred eggs through midsummer. The larvae hatch in two to three days. They are small legless maggots that range in color from creamy-white to green or brown. They look somewhat slug-like and are tapered towards the head. The larvae feed on aphids or other insects and move around on the plants in search of prey. The larvae complete their development in two to three weeks, consuming up to 400 aphids.
Hover flies pupate on the foliage near the feeding site or leave the plant and enter the soil to pupate over the winter. The pupa is enclosed within a puparium, which is the hardened skin of the last larval instar. During the growing season adults emerge in one to two weeks. Generation time depends on temperature, species and availability of food; there may be five to seven generations per year.
Hover flies can be effective in suppressing aphid populations in gardens and mixed plots. They will be most noticeable in the later half of the growing season, usually after aphid infestations are established. Because they are not as conspicuous as lady beetle adults or larvae or other aphid predators they are often not given credit for the significant effect they may have on aphid colonies.
At this time hover flies are not commercially available.
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