Moth flies are fuzzy little flies with wing veins that run parallel from base to tip. In nature, they breed in moist, polluted environments that sometimes flood, where their larvae feed on decaying organic material. In and around structures, moth flies are common in plumbing drains and sewage systems. Because moth flies develop in decaying organic material, they may carry pathogens in healthcare facilities or to food handling areas. They may also cause allergic asthma in sensitive people.