Fruit flies are most commonly brought into the home via fruits and vegetables that already contain fruit fly eggs.

Fruit fly eggs are very small (<0.

5 mm) and virtually invisible to the naked eye — the female may have already laid eggs in a tiny break in the banana peel, the stem cavity of an apple, or a crack in a tomato.

When you buy these fruits at the supermarket, the fruit fly eggs are already attached to them.

After bringing them home and storing them at room temperature for a few days, the eggs hatch into larvae that feed on the fruit flesh, and about 7–10 days later, new adult flies emerge — this is the reason "fruit flies suddenly appear even though no flies were seen flying in.

" Another source of fruit flies is the organic buildup in drains — food residue and grease accumulating in kitchen sink drains provide food for fruit fly larvae.

Storing fresh fruits and vegetables in the refrigerator (low temperatures inhibit egg hatching), taking out kitchen trash daily, and periodically flushing drains with boiling water can effectively interrupt the fruit fly life cycle.