Could be
these
As the grubs are hard to see (velly velly small) & white.
Maybe its best to empty the entire cuboards, clean them thoruoughly (use hoover too), throw away anthing that looks manky & restock using more airtight containers.
I wish I could get my lot to use airtight containers, but they are too lazy & complain that they take up too much space.
(why can't they make them cerial box shaped instead of oval??)
With your flour, get rid & only get some when you are actually going to use it, then get just what you need or dispose of the leftover packet.
Better still, if you have some left bake a loaf of bread with it etc.