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Mycetophilidae (fungus gnats; order Diptera, suborder Nematocera) Family of small flies which have long antennae, and ocelli. The tibiae have spurs, and the coxae are elongate. The thorax is more or less arched, often strikingly so. The common name refers to the usual feeding substrate of the larvae, which often live gregariously among decaying vegetable matter or in fungi. The larvae are usually pale in colour, and have a hard, sclerotized head, and 12 segments. Several species are economically important as pests of mushrooms, but others attack only wild fungi. Several species are luminous, the light being emitted from the distal part of the Malpighian tubules. Although they are similar in many respects to the Mycetophilidae, the Sciaridae (Sciarinae) are now regarded as a separate family. There are more than 2000 described species, with a world-wide distribution.