The insect order Diptera contains the true flies, including species known as gnats, mosquitoes, horse flies, and black flies. Members of this order demonstrate holometabolous development or complete metamorphosis.

As adults, true flies have one pair of wings, although there are some parasitic species that may lose their wings once they find a host. Flies are described as having mouthparts that may be piercing-sucking as in mosquitoes. Sponging mouthparts are found in the more advanced flies such as the house fly.

A distinctive feature is that members of this order will only have one pair of wings. The hind wings are modified into structures called halteres. Halteres are modifications of the hind wings that are small knobbed structures. They function as organs of equilibrium, essentially acting like gyroscopes during flight.

With regard to this order, there are about 120,000 different species worldwide with about 18,200 species known to occur in North America north of Mexico. Members in one particular beneficial family, the Tachinidae, lay their eggs on pest species and are known to be beneficial in managing pest species in landscapes.