What Bug Is That? The guide to Australian insect families.

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Dolichopodidae

Overview

Flies of the family Dolichopodidae, the 'long-legged flies',  have a characteristic habitus, comprising elongate legs usually with sparse setation, metallic thoracic colour, large eyes, aristate antenna, labellate mouthparts, and reduced venation; with a little experience, the family is readily recognised.

Taxa that superficially might be confused with Dolichopodidae include some Empididae (Microphorinae, but has cell dm present and antennal style), and various acalyptrate families (all with ptilinal suture, and often with fronto-orbital setae, genae and/or plumose arista).

Although they are good fliers, they are often cursorial on foliage, tree trunks, mud flats, intertidal reefs, river rocks, and even on the surface of ponds. Although dolichopodids favour moist habitats, they can be found in almost all Australian terrestrial environments, including the coastal littoral. However, adults of many taxa are scarce or absent during winter or dry seasons.

Dolichopodids are often abundant in Malaise trap samples, but normally many more females than males are captured. This may reflect reproductive behaviour, the males remaining near lekking sites, while mated females actively search for oviposition sites, making them more liable to interception by such passive traps. Water or pan traps also capture large numbers (yellow and white traps are particularly effective) and usually with more even sex ratios, possibly because the traps are attractive. The family is rarely collected at light. Dolichopodidae are best dry-mounted fresh, either pointed or glued to the side of a pin, but small-sized taxa have a tendency to shrivel, and storage in 75% alcohol is best in the first instance if conditions are unsuitable for immediate mounting.

The Dolichopodidae are the most derived family of the Empidoidea, with reduced venation, a hairlike antennal arista, and 360Deg twisting of the male postabdomen. Other diagnostic features include: vein Sc usually joined with R1, crossvein r-m in the basal quarter of wing, wing cells dm and bm united or only incompletely separated.

The Dolichopodidae are one of largest families of flies, worldwide with approximately 6,000 described species. At present, some 405 species in 46 genera and nine subfamilies are known from Australia (Bickel & Elliott 2001), but many more await description.

The family is often abundant in warm moist habitats. Dolichopodids are often cursorial on foliage, tree trunks, mud flats, and river rocks, even though they are good fliers. Adults are predators on such soft-bodied invertebrates as mites, thrips, psocids, aphids, small nematocerous diptera, oligochaetes, etc, and are important general control agents of many pest species. Prey are crushed between a pair of longitudinally opposed labellae and their bodily fluids absorbed through tube-like pseudotrachea within the labellae.

The larvae are maggot-like and found in such habitats as sand, soil, rotted vegetation, mud, under bark, tree holes and coastal wrack. Most are predators or scavengers; the larvae of Thrypticus are stem miners in various monocotyledons. Almost nothing is known of the immature stages of Australian species, and the sparse information on the family as a whole is based on isolated rearings of Holarctic genera, summarised and keyed in Robinson & Vockeroth (1981); also see Dyte (1959).

Dolichopodids are known for their elaborate male secondary sexual characters, assumed to aid in species recognition during courtship. Male secondary sexual characters (MSSC), which often show parallel development in unrelated groups, include flag-like flattening of the arista and tarsomeres, strongly modified setae and cuticular projections, prolongation and deformation of podomeres, orientated silvery pruinosity, maculation and deformation of wings, etc. In some cases male-female dimorphism is so striking that the association of sexes is not readily apparent. As a rule, males have a range of diagnostic MSSC and/or genitalic characters, while females of closely related species are often inseparable.

The hypopygium or male genital capsule usually has diagnostic species character states, and is often relatively large. The hypopygial peduncle, formed of the 7th abdominal segment, is sometimes prolonged, reaching an extreme development in the Australian and New Caledonian genus Atlatlia (Bickel 1986a). The Dolichopodidae show a strong convergence with the higher Diptera Cyclorrhapha in that the hypopygium is functionally rotated 360Deg, with resulting asymmetry of the postabdominal sclerites. The tiny Babindella of the endemic Australian subfamily Babindelline, however, shows secondary postabdominal symmetry (Bickel 1987b).

This family contains wingless species.

Description

Body length 0.5-10.0 mm. Adults generally of slender build, and often of metallic colouration, characteristically blue-green with bronze reflections, gunmetal black, brown, or sometimes translucent yellow. Head setation rather sparse, rarely with fronto-orbitals. Eyes occupying most of head in lateral view, without genae. Arista 2-segmented. Proboscis developed as pair of laterally crushing labellae. Legs elongate, and often with reduced setation. Wing cells dm and bm united; r-m crossvein located in basal fifth of wing or absent; radial sector 2-branched, and swollen at fork; vein A1 reduced or absent. Male abdomen usually with six symmetrical pre-abdominal segments; segment 7 modifed into arm or hypopygial peduncle; segment 8 reduced to cap-like sternum covering left lateral or sometimes basal hypopygial foramen; hypopygium or male genitalic capsule well developed. Female abdomen telescoping; oviscapt variously with dorso-apical spines or papillae, or in Thyrpticus , modified into plant-piercing blade.

The larvae are maggot-like, with the head capsule containing apically expanded metacephalic rods. Most species have four pointed lobes on the caudal segment, with the posterior spiracles positioned on the inner surface of the dorsal pair. The abdominal segments have creeping welts that sometimes encircle the body.

Distribution

Australia has an unusually rich tree trunk fauna, especially noticeable on smooth-barked eucalypts. These include the genera Medetera , Corindia , Atlatlia and Systenus (Medeterinae) Neurigona and Arachnomyia (Neurigoninae), some Diaphorus species (Diaphorinae), Achalcus (Achalchinae), some Austrosciapus , Amblypsilopus and Heteropsilopus (Sciapodinae), and Antyx (unplaced). Most of these taxa utilise tree trunks as leks or mating assemblies although feeding also occurs. Individuals tend to run or make short flights up the vertical trunk surface until reaching the canopy.

In littoral habitats, Hydrophorus and Thinophilus (subfamily Hydrophorinae), are commonly found on the mud flats of brackish lagoons, estuaries, and interior salt lakes. The bizarre endemic Paraliptus mirabilis has greatly enlarged forefemora. Cymatopus simplex inhabits the rocky intertidal zone at low tide. The brachypterous Schoenophilus pedestris is found on Macquarie Island.

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.

The Sciapodinae, generally recognised by the branched vein M1+2 and excavated vertex, is the largest and best known subfamily in Australia, with 253 described species (Bickel 1994). The subfamily shows a variety of biogeographical patterns, broadly indicative of the Australian Dolichopodidae as a whole. The genera Heteropsilopus and Parentia have classical Bassian distributions, with ties to other southern lands - India, and New Zealand and New Caledonia, respectively. The disjunction of Heteropsilopus in Australia and southern India suggests a widespread eastern Gondwanan distribution, dating from the lower Cretaceous. Sister taxon relationships between New Zealand and Australian Parentia suggest a common fauna before the opening of the Tasman Sea more than 80 m.y. B.P. Chrysosoma and Amblypsilopus are characteristic of a recent Torresian fauna of Oriental-Papuan affinity which dominates the monsoonal tropics, but has penetrated southwards along the eastern Australian coast and ranges in association with tropical and subtropical rainforest. The southern limit of Torresian taxa coincides with the southern limit of subtropical rainforest in New South Wales. Lowland Papuan species occur on Cape York Peninsula and across northern Australia. Austrosciapus is an endemic genus found primarily in eastern Australian forests. In contrast to eastern Australia, the aridity of Western Australia prevented southward movement of tropical elements, and the south-west maintains only a Bassian fauna. The faunas of Norfolk and Lord Howe Islands show Australian affinities, while those of Christmas and Cocos-Keeling Islands are of Greater Sunda origin.

The relatively small, dull-coloured Sympycninae have the male genital capsule somewhat enclosed by posterior abdominal tergites. Sympycnus (s.l.) and Chrysotimus are dominant dolichopodid elements in the temperate forests of south-eastern Australia and Tasmania. These genera show similar diversity and ecological dominance in New Zealand and southern South America, reflecting Gondwanan affinities. Nothorhaphium padicum is common and abundant throughout much of southern Australia.

The Dolichopodinae predominate in the Holarctic Region, and have an impoverished representation in Australia, primarily by the genus Paraclius . The Diaphorinae, on the other hand, are well represented throughout Australia by the cosmopolitan genera Diaphorus and Chrysotus , and by Asyndetus and Cryptophleps in the tropics.

  • Dolichopodidae larvae

  • Dolichopodidae

  • Sciapus sp.

  • Dolichopididae

  • Dolichopodidae

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