The antennae of Diptera, which are also extremely important in classification, are thread-like in the more primitive families, such as the Tipulidae (daddy-long-legs), where they consist of a considerable number of joints, all of which except the first two, and sometimes also the last two, are similar in shape; in the more specialized families, such as the Tabanidae (horse-flies), Syrphidae (hover-flies) or Muscidae (house-flies, blue-bottles and their allies), the number of antennal joints is greatly reduced by coalescence, so that the antennae appear to consist of only three joints.
Metamorphosis in Diptera is complete; the larvae are utterly different from the perfect insects in appearance, and, although varying greatly in outward form, are usually footless grubs; those of the Muscidae are generally known as maggots.
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.).
The phytophagous species are attached to various parts of plants, dead or alive; and the carnivorous in like manner feed on dead or living flesh, or its products, many larvae being parasitic on living animals of various classes (in Australia the larva of a species of Muscidae is even a parasite of frogs), especially the caterpillars of Lepidoptera, which are destroyed in great numbers by Tachininae.