Many of the adults are bloodsuckers (Tabanidae, Culicidae, &c.); others are parasitic in their larval stage (Oestridae, &c.).
Animals suffer from the ravages of bot flies (Oestridae) and gad flies (Tabanidae); while the tsetse disease is due to the tsetse fly (Glossina morsitans), carrying the protozoa that cause the disease from one horse to another.
The related species of the Oestridae family, which include the widely disseminated chigoe or bicho do pe (Pulex penetrans), and the equally troublesome berne (Cutiterebra noxialis), which is so injurious to animals, are equally numerous.
The Diptera Orthorrhapha include the more primitive and less specialized families such as the Tipulidae (daddy-long-legs), Culicidae (gnats or mosquitoes), Chironomidae (midges), Mycetophilidae (fungus-midges), Tabanidae (horse-flies), Asilidae (robber-flies), &c. The Diptera Cyclorrhapha on the other hand consist of the most highly specialized families, such as the Syrphidae (hover-flies), Oestridae (bot and warble flies), and Muscidae (sensu latiore - the house-fly and its allies, including tsetse-flies, flesh-flies, Tachininae, or flies the larvae of which are internal parasites of caterpillars, &c.).