inside and cellophane on top works too and you can see the flies. http://en.wikipedia.org/wiki/Flint " Flint  is a hard,  sedimentary   cryptocrystalline  form of the  mineral   quartz , [1] [2]  categorized as a variety of  chert ." http://en.wikipedia.org/wiki/Steel " Steel  is an  alloy  made by combining  iron  and other elements,