Common house flies can fly into a property from close by where they have been breeding in decaying organic matter (such as meat, fruit, vegetables) or faeces. These include compost piles, farms, road kill, rubbish bins – in fact anywhere there is decaying organic matter, including organic residue in your own bins. Fruit flies like sugary substances and feed and breed on overripe fruit, spilled soft drinks and alcohol residue. Drain or filth flies, as the name suggests seek moist areas to lay their eggs such as drains.