Take two squares of wood, and cut a round hole in one. Make a cone of screen wire that fits the hole, with a 1 inch opening at the top. Wrap all four sides with screen wire, and put four 1x2 support legs on the outside that holds the bottom wood, up about 8 inches.

Put some rotted food under it. and the flies will catch themselves when disturbed. They fly up, through the cone and 1 inch opening; and can't find their way out. Works well!

:)