March flies live outdoors and are a nuisance when large numbers are attracted to lights. March flies, for example, are so named because adults of some species appear in large numbers during spring and fly to windows or porch lights. Adults may swarm along roads, annoying motorists by fouling windshields. Although March flies can enter buildings, they do not reproduce or develop in buildings. Fungus gnats and moth flies can both enter buildings as flying adults and develop indoors through all life stages.
Shore flies are unlikely to reproduce indoors, except in greenhouses.
Fungus gnats, shore flies, moth flies, and March flies do not bite people or animals and, in the United States, are not known to carry human pathogens. Only fungus gnat larvae commonly damage plants indoors by feeding on roots, thus stunting plant growth. Root damage can occur in interior plantscapes and in houseplants if high populations infest frequently watered, organic-rich soil. Fungus gnat larval damage can be especially serious in greenhouses, nurseries, and sod farms. In addition to larvae chewing on roots, both larvae and adults can spread plant pathogens and may promote disease in commercial crops.