Insects of Britain and Ireland: orders

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L. Watson and M. J. Dallwitz


Two-winged flies: Bot-flies, Houseflies, Blowflies, Mosqitoes, Gnats, Crane-flies, Hover-flies, Fruit-flies, Warble-flies, etc.

Adult insects. Nearly always found near water (some forms), or not particularly associated with water. Predatory, or phytophagous, or imbibing nectar, or saprophagous, or coprophagous, or consuming stored produce, or mycophagous, or parasitic, or incapable of feeding (e.g., Oestridae. Diptera are extensively polyphagous, but while a few Empididae and Syrphidae eat pollen, the order is overwhelmingly confined to liquid foods, for which the mouth-parts are specially adapted - solids being first liquefied by salivary secretions); when parasitic, ectoparasitic on mammals, or ectoparasitic on birds, or parasitising invertebrates only. Minute to large; capable of flight, or flightless; usually with one pair of propellant wings (the forewings). Head hypognathous; as distinct from the mouthparts not rigidly beaked. Mouthparts well developed; suctorial (sometimes sponging or lapping); piercing, or not piercing; highly modified (being strongly adapted for sucking, to form a more or less elongate proboscis or rostrum which usually incorporates the bases of the maxillae, the labrum, and sometimes elements of the clypeus and even of the frons. The mandibles are usually absent in males, and often so in females, being present mainly in predators and parasitic forms in the guise of long, piercing stylets). Antennae conspicuous, or inconspicuous; complex (with a variety of forms), or simple; 2–16 segmented. Compound eyes present and well developed. Ocelli 0 (exclusively so in fifteen British families), or 2 (the median one being occasionally absent, e.g. some Cecidomyiidae), or 3 (commonly). Wings ostensibly two; the single pair membranous. Hind-wings represented by small, clubbed ‘halteres’ (these functioning as balancing organs). Wings with few cross-veins; more or less naked. Wings of the resting insect outspread, or closed and directed backwards. Tarsi typically 5 segmented. Abdomen conspicuously appendaged at the rear, or not conspicuously appendaged; with cerci clearly visible at its tip, or lacking clearly visible cerci (cerci usually very small). Abdomen of females with an exserted ovipositor, or with no exserted ovipositor. Abdomen apparently 10 segmented, or 11 segmented (10 and 11 usually being fused to form the ostensible segment 10).

Larvae. Larvae (maggots) terrestrial to aquatic (usually in moist situations, in mud, soil, decomposing organic material, in plant or animal tissues, or swimming in free water. Aquatic forms lack external gills.); feeding in the open (e.g., those of mosqitoes), or clandestine feeders (mostly); predatory, or phytophagous, or saprophagous, or coprophagous, or consuming stored produce, or mycophagous, or parasitic; without segmented thoracic legs (but unsegmented prothoracic prolegs sometimes occur); with ventral abdominal prolegs, or without ventral abdominal prolegs (often); with paired anal prolegs, or without anal prolegs (often). The abdominal prolegs when present, without crochets. Larval head without a well sclerotized capsule (only the Nematocera with a well formed head capsule, elsewhere the head being often undifferentiated and sometimes partially withdrawn into the thorax). Development of larva into adult involving marked metamorphosis; endopterygote; involving a pupal stage.

Pupae. Pupae in a puparium, or without a puparium; with articulated mandibles; with free appendages, or with the appendages fused to the body.

Classification. Subclass Pterygota; Division Endopterygota.

British representation. 102 families, described individually in the accompanying data set; genera about 1200; about 6700 species.

General comments. Most adult Diptera are immediately recognizable as such by the combination of only one pair functional wings, with the hind-wings represented by the halteres; and the few apterous forms are easily distinguishable from other two-winged insects (some Ephemeroptera, and male Coccoidea) by the mouthparts.

Illustrations. • Representative Diptera. For numerous images of Diptera from Curtis and Francis Walker, see the ‘Families of British Diptera’ data set. • Phthiria pulicaria (Sea-shore Bee-fly: B. Ent. 521). • Anthrax, adult and larva (Lubbock 1890). adult. larva.

To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: orders. Version: 16th May 2016.’.