Dust mites. Coloured scanning electron micrograph (SEM) of Dermatophagoides pteronyssinus dust mites. Dust mites have unsegmented, round bodies with mouthparts that are highly adapted to feeding on the dead scales of human skin found in household dust. They have eight legs and are relatives of spiders and scorpions. They are smaller than full stops and therefore invisible to the naked eye. Millions of dust mites live inside furniture and fabric in the average home. The dead bodies and excrement of dust mites can cause allergic reactions to household dust.