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The one I took back was a brand new bag - opened it at home and saw the mites/weevils. You don't have to look hard, they crawl about the bag, just tiny little black lines. When I took it back, the woman at Customer Services said she had the same problem and only bought flour in small quantities. She said the eggs can be in the flour and then you get the little blighters. I got a new bag and opened it right away in the shop to make sure it was okay. So I don't think it's a problem with my cupboard. I shall try atalanta's tip of keeping flour in the freezer - does it all clog together and then need defrosting before use?