[header] How to repel insects with beer [title] Kill fruit flies with an open beer can. [step] Fruit flies (also called vinegar flies) are attracted to fermented beverages like beer and wine. For an effective fruit fly trap, leave an open beer can sitting out with a small piece of paper taped over the lid. 
Poke a small hole in the paper to allow the flies to enter the can. They will be unable to find their way out and will eventually drown in the beer.