The larvae of gall midges are apodous, have no recognisable head or mouthparts; when full grown they often are bright yellow, orange or red in colour. They pupate in a cocoon, but a few species make a puparium, which is exceptional for Nematocera. The larvae of a number of species are carnivorous (feeding on gall mites, aphids or other gall midge larvae) or feed on fungus spores (on a leaf that is attacked by rust fungi they are almost invariably present), but the majority is phytophagous. They are hidden deep in a fold, sometimes in a cavity or fruit and produce saliva containing digestive enzymes that after some time is re-ingested (extra-intestinal digestion).
The ovipositor is relatively long, retractable, but usually not heavily sclerotised. To penetrate deeper in a plant therefore sometimes galleries are used that have been made by other insects, or the sponge parenchyma is reached through a stoma (e.g. in Cystiphora).
Many larvae have in their third, last instar ventrally on the thorax a slender chitinous rod, the spatula that often ends anteriorly with two or three teeth.
Larvae of the genus Contarinia, are able to jump.
Larvae of the genera Asphondylia and Lasioptera live in symbiosis with phytophagous fungi. The females have specialised organ to store fungal spores and to deposit them during oviposition (Thomas & Goolsby).
Joy (2009a), Mamaev & Krivosheina (1993a), Skuhravá (1991a), Richards & Davies (1977a), Rohfritsch (2011a), Skuhravá (1997a), Thomas & Goolsby (2015a), Tokuda (2012a).