The trap that Possum Hunter posted is the exact same one I use. The longer it hangs there, the worse it smells, the more dead flies it gets in it, and the better it works.

If my people, who are called by my name, will humble themselves and pray and seek my face and turn from their wicked ways, then will I hear from heaven and will forgive their sin and will heal their land. 2 Chronicles 7:14