Where there is fruit followed by fruit flies .. Leave, for example, a banana outside for a few days and you will suddenly find these tiny insects scattered everywhere on the fruit and on the walls.
They can get rid of them using a vacuum cleaner but there is a better way to eliminate this flies. Mix a small glass of apple juice, washing means and a little vinegar and leave it next to the fruit plate.
A few hours later you will notice that the acidity and sweetness of apple juice attracted most flies, while the washing liquid will make it difficult for flies to stand on the water.