Family DOLICHOPODIDAE Latreille, 1809

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• Dolichopodes Latreille, 1809.

  Type genus:

   Dolichopus Latreille, 1797.

Introduction

Flies of the family Dolichopodidae, the 'long-legged flies', are generally of slender build, range in body length from 1 to 10 mm, and are usually at least partially metallic in colour. Although they are good fliers, they have relatively long legs (as the family name implies), and are often cursorial on foliage, tree trunks, mud flats, intertidal reefs, river rocks, and even on the surface of ponds. Overall, dolichopodids favour moist habitats. They are readily collected and often taken in large numbers in malaise and yellow pan traps, as well as by sweeping.

The Dolichopodidae are the most derived family of the Empidoidea, with reduced venation, a hairlike antennal arista, and 360 degree 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.

Adult dolichopodids are voracious predators on soft-bodied invertebrates such as mites, thrips, psocids, aphids, insect larvae and aquatic oligochaetes, and in economic terms are important in the general control of many pest species. Prey are crushed between a pair of longitudinally opposed labellae and their body fluids absorbed through tube-like pseudotrachea.

Dolichopodids are known for their elaborate male secondary sexual characters, assumed to aid in species recognition during courtship display. Male secondary sexual characters, which often show parallel development in unrelated groups, variously include flag-like 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. In some cases male-female dimorphism is so striking that the association of sexes is not readily apparent.

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

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. Dolichopodid larvae are found in a variety of habitats, most often in sand or mud along springs, rivers and ponds, in rotting vegetation, tree holes, under bark, or in coastal wrack. Most are predators or scavengers, although the larvae of Thrypticus are stem miners in various monocotyledons. Almost nothing is known of the immature stages of Australian species (see Dyte (1967) for a review of the immature stages).

The Dolichopodidae are one of largest families of flies, worldwide with approximately 7100 described species. At present, more than 430 described species in 50 genera are known from Australia but many more await description.

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 254 described species. 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 and 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 southwest maintains only a Bassian fauna. The faunas of Norfolk and Lord Howe Islands show Australian affinity, 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 southeastern 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.

General References

Dyte, C.E. 1967. Some distinctions between the larvae and pupae of the Empididae and Dolichopodidae (Diptera). Proceedings of the Royal Entomological Society of London (A) 42: 119-128

Germann, C., Pollet, M., Wimmer, C. & Bernasconi, M.V. 2011. Molecular data sheds light on the classification of long-legged flies (Diptera : Dolichopodidae). Invertebrate Systematics 25: 303–321

Sinclair, B.J. & Cumming, J.M. 2006. The morphology, higher-level phylogeny and classification of the Empidoidea (Diptera). Zootaxa 1180: 1-172

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