Diptera (Two-Winged or True Flies)
Insects with a single pair of membranous wings, the hind pair modified into halteres. Mouthparts suctorial, usually forming a proboscis and sometimes adapted for piercing: mandibles rarely present: labium usually distally expanded into a pair of fleshy lo
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DIPTERA (TWO-WINGED OR TRUE FLIES) Insects with a single pair of membranous wings, the hind pair modified into ha/teres. Mouthparts suctorial, usually forming a proboscis and sometimes adapted for piercing: mandibles rarely present: labium usually distally expanded into a pair of fleshy lobes. Prothorax and metathorax small and fused with the large mesothorax: tarsi commonly s-segmented. Metamorphosis complete, larvae cruciform and apodous, frequently with the head reduced and retracted: tracheal system variable, most often amphipneustic, pupa either free or enclosed in the hardened larval cuticle or puparium, adecticous, primitively obtect but in higher forms exarate: wing-tracheation reduced.
The Diptera are one of the largest orders of insects including over 85 ooo described species, and approximately 5200 species are known from the British Isles. Structurally Diptera are among the most highly specialized members of their class. The imagines of most species are diurnal and the majority are either flower-lovers, which feed upon nectar, etc., or frequently decaying organic matter of various kinds. Although these two habits predominate, a considerable number of flies are predacious and live on various insects. In addition to the foregoing, there are other Diptera which have acquired blood-sucking habits, and besides man many other vertebrates may be resorted to by one or other species. Excluding the Muscidae and the so-called Pupipara, this habit is largely confined to the female. The blood-sucking forms include almost the whole of the Culicidae, besides the Simuliidae, Phlebotominae, Tabanidae and the Glossinidae and allied forms, also certain members of the Ceratopogonidae and Muscidae. In virtue of this propensity the order has acquired great medical significance. The pathogenic organisms of some of the most virulent diseases such as malaria, sleeping sickness, elephantiasis and yellow fever are transmitted to man through the intermediary of blood-sucking Diptera. External Anatomy The work of Crampton (1942) forms a useful introduction to the external anatomy of the Diptera. O. W. Richards et al., Imms’ General Textbook of Entomology © O. W. Richards and R. G. Davies 1977
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GENERAL TEXTBOOK OF ENTOMOLOGY
The Head (Fig. 438) is remarkable on account of its mobility and i~ usually of relatively large size. An extensive portion of its area is occupied b) the compound eyes which, as a rule, are considerably larger in the male thar the female. When the eyes of the two sides are contiguous they are stated tc be holoptic, and when markedly separated dichoptic; very occasionally tht holoptic condition is found in the female as well as the male. In some specie! the upper facets are larger and more conspicuous than the lower, a peculiarity rarely seen in the female. It assumes its most extreme development in tht Bibionidae where the two areas of different facets are sharply defined (Fig 84). Between or slightly behind the eyes are the ocelli: the latter are usuall) three in number and are generally arranged in the
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