Cheap and Simple Homemade Fruit Fly Trap

I'm not sure why, but we've had an infestation of fruit flies in the kitchen lately. One morning, I found four or five of them hovering around a banana peel, and remembered a trick someone had told me.

I wrapped an 8 1/2 by 11 sheet of paper in to a funnel shape, taped it securely to a canning jar with the offending banana peel in the bottom, and left it out on the counter. The next morning, this is what I found:

Apparently, the flies go down the funnel following the smell of the banana peel, but then try to get out by flying toward the light, getting trapped at the top of the jar (this is why you need to be careful to tape the funnel securely to the jar, leaving no gaps). Simple and effective!