Fruit flies develop by complete metamorphosis. The eggs (difficult to see with the naked eye) are deposited near the surface of fermenting fruit or organic matter. A pair of filaments that are attached to the eggs protrudes above the surface of the liquid. The female fruit fly will lay about 500 eggs. The larvae emerge about 30 hours after the eggs have been laid and feed near the surface of the fermenting material. The larvae feed for five to six days then crawl to drier areas of the food source or even out of the food source to pupate. The larva transforms into the pupa in the last larval skin, or puparium, which bears a conspicuous pair of filaments on the anterior end. The adult fruit fly emerges several days later.
The newly emerged fruit flies are attracted to light and become sexually active in about two days. The adults mate more than once. Under ideal conditions, the life cycle from egg to adult can be completed in as little as eight days. The sudden appearance of large populations is not uncommon inside buildings.
When searching for fruit fly breeding sources, remember that the larva can only survive in decaying organic matter that is moist. The first obvious place to check is where any fruits or vegetables or stored outside of refrigerators or coolers. Other areas to inspect would be recycling bins, seldom used (or cleaned) garbage cans, underneath and behind large appliances. Do not overlook drains where small flies are often found breeding in the super thin layer or film of debris that naturally accumulates in pipes, traps and drains.