Therevidae Burmeister, 1837

Small to medium-sized (2.5-18.0 mm) lower Brachycera with short, usually stiletto-like antennal flagellum and elongate or tapered abdomen. Margin of eyes in males meeting at mid-line of upper frons or separated by less than width of ocellar tubercle, widely separated in females with darker tomentum or bare medial areas (often appearing as a single spot or pair of shining spots); proboscis arising from subcranial cavity, labella fleshy; antennal scape and pedicel setose, first flagellomere with or without setae, antennal stylus short and composed of one to three small apical or subapical flagellomeres. Thoracic and scutellar bristles present. Wing membrane clear to opaque, often darker adjacent to cross-veins and distal wing veins, occasionally maculated; discal cell elongate with M1, M2, and M3 arising from its apex. Legs slender, bristles present on femora and tibiae; tibial spurs absent; empodium setiform or absent. Abdomen with eight pregenital segments, separated by light-coloured lateroapical tomentum or cuticle and/or yellowish-white intersegmental membrane; abdomen in males of some species uniformly greyish-white due to dense tomentum and/or adpressed setae. The larvae are elongate predators found in dry or friable substrates including sand dunes and leaf litter; and the known prey includes larvae and pupae of Coleoptera, Lepidoptera and Diptera. Adults are not predaceous but have been observed drinking water or plant and animal secretions (Holston & Niehuis 2002, Spitzer & Barták 2000). Malaise traps have been effective in collecting species in riparian and steppe environments; they can also be hand-collected from the ground in sunny, open habitats or from herbaceous or woody vegetation. They are relatively rare and inconspicuous flies, and several Czech species (Cliorismia ardea, Thereva apicalis, T. microcephala, Pandivirilia melaleuca, P. eximia) are of local and regional conservation interest in northern European, and many European species are associated with xerothermic habitats (Holston & Niehuis 2002, Keil 2003,  Lyneborg & Spitzer 1974, Spitzer & Barták 2000).

Of the 98 European species (Lyneborg 1989), 29 stiletto fly species (which includes 20 Thereva spp.) are recorded in this checklist: 27 for the Czech Republic (22 for Bohemia, 26 for Moravia) and 24 for Slovakia. The genera can be identified with the key to Palaearctic Therevidae (Majer 1997), with keys and diagnoses for species dispersed among several taxonomic revisions (Lyneborg 1968, 1984, 1986a, b). The ecology and distribution of species in the Czech Republic and Slovakia are comprehensively reviewed by Keil (2003, 2005). Thereva unica Harris, 1780, is a senior synonym of Thereva bipunctata Meigen, 1820, following the nomenclature used in the Catalogue of Palaearctic Diptera (Lyneborg 1989) and the Fauna Europaea (Holston 2007).