Dust is what dust mites eat.
They specifically eat dust-borne human skin cells. (They are less concerned with the dust's inclusion of dirt, soot, and pollen.) According to the Asthma and Allergy Foundation of America, you shed 1.5 grammes of skin each day (AAFA). Although it may not seem like much, that will feed a million dust mites. Yes, you read that correctly. Dust mites number one million.