Dolichopodidae, the long-legged flies, are a large, cosmopolitan family of true flies with more than 7,000 described species in about 230 genera. The genus Dolichopus is the most speciose, with some 600 species.
Dolichopodidae generally are small flies with large, prominent eyes and a metallic cast to their appearance, though there is considerable variation among the species. Most have long legs, though some do not. In many species the males have unusually large genitalia which are taxonomically useful in identifying species. Most adults are predatory on other small animals, though some may scavenge or act as kleptoparasites of spiders or other predators.
The Dolichopodidae includes the subfamily Microphorinae, formerly placed in the Empididae, and at one time considered a separate family.
For clarification of technical terms see Morphology of Diptera
Dolichopodidae are a family of flies ranging in size from minute to medium-sized (1mm.-9 mm). They have characteristically long and slender legs, though their leg length is not as striking as in families such as the Tipulidae. Their posture often is stilt-like standing high on their legs, with the body almost erect. In colour most species have a green-to-blue metallic lustre, but various other species are dull yellow, brown or black.
The frons in both sexes is broad. The eyes are contiguous on the frons of males, except Diaphorus species, whose males have non-contiguous, but close-set eyes. On the heads of most species the ocellar bristles and outer vertical bristles are well developed. The face of some species is entire; in others it is divided into two sections: the epistoma and the clypeus. The largest antennal segment is the third; in most species it bears a long arista, which is apical in some species, dorsal in others. In most species the mouthparts are short and have a wide aperture as an adaptation for sucking small prey.
The legs are gracile and the tibiae usually bear long bristles. In some genera the legs are raptorial. In some species the tibiae of the males have modifications.
Dolichopodidae wing veins. This is one major type, with M1 bent and M2 present, though often incomplete. In another type, M2 is absent and M1 more or less straight
The wings of most species are clear or tinged, but some species have wings that are patterned in strong colours or with distinct spots. There are three radial veins (R1, R2+3, R4+5). The medial vein M1+2 is simple or, rarely furcate, as in the genus Sciapus. The anterior cross-vein is in the basal part of the wing. The posterior basal wing cell and the discoidal wing cell are always fused. The anal cell of the wing is always small. There are two veins branching from cross-vein DM-Cu in the direction of the wing margin; the upper one in some species curves strongly or forks into M1 and M2.
The abdomen is elongate-conical or flat. The genitalia of the male often are free and borne on a petiole, with tergite 8 being asymmetrical, lying on the left side of the epandrium. Males of most species have well developed gonopods of two or three lobes on the distal margin of the epandrium. The gonopods may fuse with the epandrium in genera such as Hydrophorus, Thrypticus and Argyra, or there may be a suture, as in the genera Porphyrops, Xiphandrium and Rhaphium. In some genera, such as Hypophyllus and Tachytrechus, the surstyli are well-developed as secondary outgrowths of the epandrium. In genera such as Tachytrechus, there are two pairs of surstyli – one proximal and one distal. The hypandrium in most species is a small sclerite, which may be asymmetrical as in the genera Porphyrops and Tachytrechus. Males of many species have highly developed cerci. Development of the phallus varies considerably between genera.
The species found in Australasian and Oceania:
Flies of the family Dolichopodidae are often abundant in moist habitats and are frequently found on foliage, tree trunks, mud flats, and river rocks. Adults are predaceous on soft-bodied invertebrates and serve as important general control agents of many pest species.
The maggotlike larvae are found in such habitats as soil, rotted vegetation, mud, and under bark. Most are predators or scavengers, although the larva of Thrypticus is a phytophagous stem miner in various Monocotyledons
The elaborate secondary sexual characters of male dolichopodids are assumed to aid in species recognition during courtship and often show parallel development in unrelated groups. These characters include flaglike flattening of the arista and tarsi, strongly modified setae and cuticular projections, prolongation and deformation of podomeres, orientated silvery pruinosity, maculation and deformation of wings, etc. The hypopygium is often greatly enlarged and exposed and usually carries species-specific characters. The tiny Babindella, of the endemic Australian subfamily Babindellinae, shows secondary postabdominal symmetry (Bickel 1987b).
The Dolichopodidae is one of the most diverse families of flies, with approximately 7,000 described species worldwide. In the Australasian/Oceanian Regions, 1181 species representing 91 genera in 11 subfamilies are currently known, although many new species and genera await description, especially from Australia and the Melanesian Archipelago. Apart from southern temperate elements in New Zealand and Australia, much of the Australasian/Oceanian fauna has strong affinities with that of the Oriental Region. A notable exception is the presence of the Neotropical Condylostylus longicornis in eastern Polynesia.
Some “tramp” species, such as Medetera grisescens and Chrysosoma leucopogon, show extraordinarily widespread distributions throughout both the Oriental and Australasian regions, including many isolated oceanic islands. Several brachypterous species are known from subantarctic islands. Of particular interest is the extensive speciation of Campsicnemus in the Hawaiian Islands (138 spp., with many more awaiting description). This radiation invites comparison with that of the well-studied Hawaiian Drosophila.
The subfamily arrangements followed here are based on Ulrich (1981), with modifications. The limits of certain subfamilies, such as the Diaphorinae and Sympycninae are unclear and some genera, such as Sympycnus, are polyphyletic assemblages. Recent revisionary studies on the Medeterinae (Bickel 1986a,b,c, 1987c) and Hydrophorinae (Grootaert & Meuffels 1984, Meuffels & Grootaert 1984) have added to the regional understanding of these taxa.
Becker’s (1922b) monograph, although dated, remains the basic reference for both the Oriental and Australasian/Oceanian regions. Important faunistic treatments include those on the Hawaiian Islands (Hardy & Kohn 1964, Tenorio 1969), New Zealand (Parent 1933b), Australia (Hardy 1930a, 1935b, 1939c; Parent 1932a, 1933a), Samoan Islands (Lamb 1929), and New Guinea (de Meijere 1906b, 1913a,b, 1915b; Parent 1939a). Additional species descriptions are found in the many papers of Parent. Robinson & Vockeroth (1981) provided a well-illustrated general review of the family.