Phylogenetic position and definition of the Therevidae
The Therevidae are placed in the lower Brachycera in the super-family Asiloidea. The Asiloidea comprise the families Bombyliidae, Asilidae, Apioceridae, Mydidae, Therevidae, and Scenopinidae and is united by a hinged metacephalic rod (Woodley 1989). The relationship between the families is unclear, but the most accepted hypothesis of relationship is (Bombyliidae (Asilidae (Apioceridae+ Mydidae) (Therevidae+ Scenopinidae))) (Woodley 1989, Sinclair et al. 1993).

The sister group relationship of the Therevidae and Scenopinidae is unambiguously supported by the secondarily segmented larval abdominal segments, thus appearing to have seventeen segments (Woodley 1989). Woodley (1989) also suggested that the small pair of caudal prolegs in the larvae may also be autapomorphic for the two families. Sinclair et al. (1993) proposed the retraction or absence of the lateral ejaculatory processes (=apodemes) within the base of the phallus as a synapomorphy for the two families. This is contrary to Yeates (1992), who figured the enlarged lateral ejaculatory apodemes of Bonjeania clamosis Winterton & Skevington. Sinclair et al. (1993) argued instead that these were additional lobes not associated with the sperm sac and therefore not homologous with the lateral ejaculatory apodemes. Based on genitalic muscular evidence, Winterton et al. (2000) subsequently supported the conclusion of Yeates (1992) that these structures were indeed the lateral ejaculatory apodemes and showed that the size of the lateral ejaculatory apodeme varies considerably across the Australian Therevidae. The interpretation by Sinclair et al. (1993) that reduced or absent lateral ejaculatory apodemes is synapomorphic for the Therevidae+ Scenopinidae is not supported elsewhere.

The morphology of adult therevids is generalised and plesiomorphic (Lyneborg 1992) and there are few convincing autapomorphies supporting Therevidae as a group. Yeates (1992) and Woodley (1989) suggest that the Scenopinidae may “represent a highly autapomorphic group that has evolved from within the Therevidae, and as such may render the Therevidae paraphyletic”. Presently, the only defining synapomorphy that separates the Therevidae from the Scenopinidae is the posteriorly spatulate larval metacephalic rod (Woodley 1989). The lack of knowledge of immature stages of many species of Therevidae means that this definition is yet to be fully tested.

Subfamilial classification of Therevidae
The Australasian therevid fauna represent a highly species rich endemic group restricted to Australia, Papua New Guinea, far eastern Indonesian archipelago, New Zealand, New Caledonia and Fiji. Only one genus, Irwiniella Lyneborg, is found outside of the region and extends into the Oriental and Afrotropical regions. Using male and female genitalic features, Lyneborg (1976) and Irwin & Lyneborg (1981a) divided the Ethiopian and Nearctic therevid faunas into two subfamilies, the Therevinae and Phycinae. This classification can be applied successfully to the Therevidae from all geographic regions of the world except Australasia. In Australasia only Anabarhynchus Macquart, Irwiniella and Megathereva Lyneborg can be placed in one of these subfamilies- the Therevinae. Winterton et al. (2001) subsequently erected a third endemic Australasian subfamily, Agapophytinae to accommodate a number of genera. The rest of the Australasian fauna is currently placed in a likely paraphyletic grouping called the Taenogera genus-group (Winterton et al. 1999b).

Summary phylogeny of Australian Therevidae relationships. While Agapophytinae are well established as monophyletic, Taenogera genus-group is not confirmed as monophyletic. The Australasian therevine genera are an independent endemic lineage with closer relatives in South America.

The Taenogera genus-group and Agapophytinae represent an intermediate grouping between the Phycinae and Therevinae, exhibiting apomorphic and plesiomorphic character states represented in each subfamily. The Agapophytinae contains the genera Acatopygia Kröber, Acraspisa Kröber, Acupalpa Kröber, Agapophytus Guérin, Belonalys Kröber, Bonjeania Irwin & Lyneborg, Parapsilocephala Kröber, Laxotela Winterton & Irwin, Patanothrix Winterton and Pipinnipons Winterton. All genera of this tribe are united by the presence of elongate velutum patches on the ventral surfaces of the fore and hind femora, and velutum on the postero-ventral surface of the gonocoxites.

The Taenogera genus-group contains Taenogera Kröber, Ectinorhynchus Macquart, Taenogerella Winterton & Irwin, Actenomeros Winterton & Irwin, Nanexila Winterton & Irwin, Eupsilocephala Kröber, Johnmannia Paramonov, Squamopygia Kröber, Manestella Metz and Neodialineura Mann (Winterton et al. 1999a,b, Metz et al. 2003). This genus-group is separated from the Agapophytinae by the absence of femoral and gonocoxal velutum patches, fused female accessory gland ducts to form a common duct, and the presence of an antero-ventral seta at the apex of the hind femur. The Taenogera genus-group is largely defined by plesiomorphic characters and its membership is still tentative pending further study. To date, no extensive cladistic studies have recovered the Taenogera genus-group as a monophyletic grouping.

The major groups of the Therevidae have distinct distributional patterns. The Phycinae are distributed through-out the Afrotropical, Neotropical and Nearctic regions, while the Therevinae are distributed throughout the Neotropical, Oriental, Australasian and Holarctic regions (Irwin & Lyneborg 1981, Irwin & Lyneborg 1989, Lyneborg 1992). The Taenogera genus-group and Agapophytinae are endemic to Australasia. The Taenogera genus-group is known from Australia and New Zealand while Agapophytinae is known from Australia and the Indo-Papuan archipelago.

Phylogenies have been proposed for the Agapophytinae based on morphological and molecular evidence by Winterton et al. (2001) and Hill & Winterton (2004), and the Taenogera genus-group based on morphological evidence by Winterton et al. (1999b). A summary phylogeny is presented here.

Recently Christine Lambkin has investigated Therevidae phylogenetic relationships by mining published phylogenies on the group using a controversial methodology called Supertree analysis. Read more on this ongoing research here.

Taxonomic History of Australian Therevidae

The Australasian therevid fauna comprises over 300 described species in 24 valid genera, however there are more than 300 undescribed species represented in collections and more new species still being collected (unpublished data). There are at least seven undescribed genera known that will soon be published and some genera awaiting revision such as Parapsilocephala Kröber and Acraspisa Kröber that each have approximately 100 undescribed species represented in collections. Clearly, the Australasian Stiletto-fly fauna is a significant endemic radiation of therevid biodiversity that we are only now starting to document adequately.

The Australasian Therevidae have been relatively poorly studied compared to other biogeographic regions. The first genus described from Australia was Agapophytus by Guérin (1831). Macquart (1846, 1847, 1848, 1850) described 14 species of Therevidae from Australasia in Anabarhynchus and Ectinorhynchus. All but one (Taenogera nitida (Macquart)) still belong in these genera. Anabarhynchus and Ectinorhynchus subsequently became “dump” groups for many species described from not only Australia, but also Africa and South America (e.g. Kröber 1931). Walker (1835, 1848, 1850, 1852, 1854, 1856) produced rather brief descriptions for 21 species of Australasian Therevidae, most of which he placed in Thereva.

Kröber (1912a-f, 1913, 1928, 1929, 1932) produced numerous treatments on Australasian therevids in which 42 new species and nine of the 20 presently recognised genera were described. Only three Australasian genera described by Kröber subsequently proved to be synonyms (Irwin & Lyneborg 1989), and is a testimony to the taxonomic skill of Kröber despite his ignorance of internal genitalic features.

The Tasmanian Therevidae were revised by White (1914, 1915) who described 17 new species and two genera, many of which were collected from a private fauna reserve north of Hobart called Chauncyvale preservation area.

The next comprehensive familial revision of the Australian Therevidae was by Mann (1928, 1929 & 1933), in which he gave preliminary keys to genera and species, and detailed descriptions of 28 new species. This series of papers was the first and last, complete revision of the family in Australia until the late 1990's, although some genera and species were simply not recognised, and often for reasons unknown.

Very little was published on the Australian Therevidae since the works by Kröber and Mann, although several single species descriptions were produced sporadically (Hardy 1939, Paramonov 1950, Hardy 1955, Irwin & Yeates 1995).

The concepts of the Holarctic genera Psilocephala Zetterstedt and Thereva Latreille were widely applied to the Australasian fauna by workers until recently, resulting in many species being initially placed into these two genera. Members of the endemic Australasian Agapophytus are difficult to separate from the Afrotropical Phycus Walker due to similarities in antennal shape, which was noted by various workers on Australian therevids (Schiner 1868, Kröber 1928, White 1915, Mann 1929). We now understand that all these aforementioned genera do not occur in the Australasian region, and the Australasian species described in Psilocephala, Thereva and Phycus were subsequently and still are being reassigned to new genera (e.g. Metz et al. 2003).

Irwin & Lyneborg (1989) compiled a catalogue of Australian and Oriental Therevidae, and re-evaluated the generic placement of many species based on genitalic characteristics. Unfortunately, this reorganisation left 12 species incertae sedis, awaiting descriptions of new genera to accommodate them. Many of these species have subsequently been placed in other genera (see Winterton et al. 1999a,b, 2000, 2001, Metz et al. 2003).

The most recent studies on Australasian Therevidae and the first using cladistic methodology were by Winterton et al. (1999a,b). These studies introduced a standardised terminology for male and female genitalia and vestiture. Moreover, the enigmatic Taenogera genus-group was recognised, while a new subfamily, Agapophytinae was described based on molecular and morphological data. The existence of the spermathecal sac complex in the female reproductive system was first noted in Winterton et al. (1999a), and subsequently the histology and morphology examined and a possible biological function proposed (Winterton et al. 1999c). Recently various genera have been revised, such as Acupalpa Kröber (Winterton 2000), Agapophytus Guérin (Winterton & Irwin 2001), Bonjeania Irwin & Lyneborg (Winterton et al. 2000) and Taenogera Kröber (Winterton et al. 1999b). In addition, several new genera were described, including Taenogerella Winterton & Irwin, Actenomeros Winterton & Irwin (Winterton et al. 1999b), Nanexila Winterton & Irwin (Winterton et al. 1999a), Laxotela Winterton & Irwin (Winterton & Irwin 1999), Pipinnipons and Patanothrix Winterton (Winterton et al. 2001).

Lyneborg (1992) and (2001) revised the highly species-rich genus Anabarhynchus, raising the number of valid species in that genus to 160, the greatest number of species in any genus of Therevidae. Based on the number of undescribed species of Anabarhynchus still in collections, the number of species in this genus may ultimately exceed 200.

Presently, major revisions are being undertaken by individual authors on Ectinorhynchus (CLL) and Parapsilocephala (SLW), with still more new genera being described. As new genera and species are described this Lucid key will be updated online as an ever-evolving process.