This small funnel fits the top of a small canning jar. Put old fruit in the jar and put this funnel in the top and screw on a lid. The flies smell the fruit and go in but they cannot figure out how to get out again. With the fruit that started the problem as bait this little trap will clean them up in a couple of days without chemicals.

Update: The trap works well but they seemed a little slow to go in. I started thinking maybe I could catch more if the hole was a little larger so I made another version. I like the look of this one better.