Dip'tera (Gr., 'two-winged'), a large order of two-winged insects, distinguished even by Aristotle, includes the house-fly, blow-fly, midge, daddy-long-legs, gnat, mosquito, &c. The most important general characters are as follows: The wings are two, transparent, never folded, with predominant longitudinal veins; the hind-wings are transformed into small 'balancers' or 'halteres,' rarely absent; the mouth organs are adapted for piercing and sucking, the palps on the first pair of maxillæ are free or absent, those of the second pair are modified into a tongue or labella; there is a complete metamorphosis (larva, pupa, and imago); the larva is a footless maggot or a grub with secondary feet, its mouth parts are adapted for biting or for sucking; those of the pupa are adapted for sucking. The order is very large, numbering probably from 15,000 to 18,000 species, not including the fossil forms preserved in amber and the like. Many species, both as adults and as larvæ, are directly or indirectly of economic importance because of their attacks on man, domestic animals, household stores, and cultivated plants; others again mitigate the ravages of other insects. The order will be sufficiently illustrated under separate articles—e.g. BLOW-FLY, CORN INSECTS, DADDY-LONG-LEGS, FLEA, GNAT, HESSIAN FLY, HOUSE-FLY, MOSQUITO, &c. See
Löw, Beschreibung europäischer Dipteren (1869-73); Taschenberg, Die Flöhe (1880); and F. Walker, Insecta Britannica: Diptera (1851-56).