The flour mite, Acarus siro, a pest of stored grains, is one of many species of grain and flour mites. An older name for the species is Tyroglyphus farinae.
The flour mite, which is pale greyish white in colour with pink legs, is the most common species of mite in foodstuffs. The males are from 0.33–0.43 millimetres (0.013–0.017 in) long and the female is from 0.36–0.66 mm (0.014–0.026 in) long.
Flour mites contaminate grain and flour by allergens and they transfer pathogenic microorganisms. Foodstuffs acquire a sickly sweet smell and an unpalatable taste. When fed infested feeds, animals show reduced feed intake, diarrhea, inflammation of the small intestine, and impaired growth. Pigs have their live-weight gain, feed-to-gain ratio, and nitrogen retention markedly reduced by infested feeds.
Flour mites are intentionally inoculated into Mimolette cheese to improve the flavor. When used for this purpose, they may be referred to as "cheese mites".
If a person is bitten from a flour mite they might suffer a reaction called Baker's itch.