Cecidomyiidae Macquart, 1838

Small flies, minute to medium-sized (0.5-3.0 mm), rarely 8 mm, very fine and fragile, usually dark in colour, sometimes with a grey, yellow or reddish coloured abdomen. Head with holoptic eyes in both sexes, ocelli present in most Lestremiinae, absent in Porricondylinae and Cecidomyiinae. Antenna with 6 to 40, usually 12 or 14, flagellomeres, covered with microtrichia or whorls of long setae or circumfila or sensoria. Wing veins reduced in number, usually only three or four long veins present. Legs usually long, first tarsomere (metatarsus) much shorter than second tarsomere except in Lestremiinae. Tibial spurs absent. The larvae have on the ventral side of the prothoracal segment a spatula sternalis, a sclerotised organ, which is unique to the family and important for identification at the specific level. The larvae are phytophagous, mycophagous, saprophagous or zoophagous. Many phytophagous larvae are gall makers, inducing galls on various plants (in Latin: cecidium, hence the name of the family), whilst some live free in flower heads or in the stems of plants without forming galls. Several species are serious pests of cultivated plants and forest trees but, on the other hand, several phytophagous species are used in the biological control of weeds. Zoophagous larvae are predators of other gall midges, aphids, mites, coccids, or other small arthropods. Some of them are used in the biological control of pests. Mycophagous and saprophaguos larvae are associated with fungi. The life span of an adult is very short, only few hours or five days at the most.

Altogether 5700 species are known to occur in the world (Gagné 2004), of which about 3200 occur in the Palaearctic Region and 1700 in Europe (Skuhravá 2005a). 602 species are listed in the present checklist: 559 in the Czech Republic (466 in Bohemia, 463 in Moravia), and 380 in Slovakia). Since the ECV1, the number of species has increased in the Czech Republic by ten (ten in Bohemia, eight in Moravia) and in Slovakia by 18.

Systematic faunistic investigations have been carried out at 670 localities in the Czech Republic (Skuhravá 1994a, b) and at 336 localities in Slovakia (Skuhravá 1991). The faunas of the Czech Republic and of Slovakia were summarised, analysed and evaluated from the zoogeographic point of view by Skuhravá (1991, 1994a, b). The fauna of Cecidomyiidae is well known in the Czech Republic and in Slovakia, and both countries are among the best explored countries of the world. 64 species are included in the red list of threatened species of the Czech Republic, 32 of them as regionally extinct, 16 as critically endangered and 16 as endangered (Skuhravá 2005b). Other seven species are alien in the fauna of the Czech Republic (Šefrová & Laštůvka 2005, Mlíkovský et al. 2006).

The basic characteristics of the family were given by Skuhravá and Skuhravý (1960) and Skuhravá et al. (1984). The galls of gall midges may be identified using the keys by Houard (1908-1909), Buhr (1964-1965), Redfern et al. (2002) and Skuhravá and Skuhravý (1992), the larvae by Möhn (1955), and the adults by Skuhravá (1997a). The nomenclature follows Skuhravá (1986, 1989) and Gagné (2004).