The worst is those little larva things can burrow in between the lid of your Tupperware and get in. They seem to like all rice, grains and cereal. Little buggers can wreck havoc if you don't catch them quickly. I'm pretty sure mine came from some stuff I bought in bulk bins, but I have seen them in previously unopened flour too. Ewwwww just gave myself the heebee jeebies and I suddenly feel the need to clean out my pantry.