How do you raise fruit flies?

All you have to do to raise fruit flies is put some fruit in a jar with no lid. Grapes with no skin or bananas work well. When there are several flies in the jar, put a paper towel over it and rubber band. Put more banana in every week or so. This works best in summer or whenever it is above 60 degrees in the day for more than a week. Of course, you can also buy a kit from the internet.