The adult flies mimic bees and may be mistaken for the predatory flower flies discussed in the previous section. The larvae attack the eggs or immatures of grasshoppers, beetles, moths, bees, and wasps. Nematodes are hair-like worms found naturally in the soil. Many are microscopic in size and vary in life-style. The parasitic forms generally feed on insects that are found in the soil during one or more stages of their life cycle, such as white grubs, root maggots or weevils.
Some forms are available commercially for insect control.
The advantages of using a parasite to control an insect is that they tend to be very specific, and attack only one or a few closely related species. Some have short life spans, and can build up to high numbers quickly. An example of a successful use of parasites is to control flies in dairy barns. The parasitic wasp lays an egg in the pupa of the fly, and thus prevents emergence of the adult. Dairy farmers must change their management practices in order to maintain the wasps, however.