Dust mites. Coloured scanning electron micrograph (SEM) of a number of house dust mites (Dermatophagoides pteronyssinus). Millions of dust mites inhabit the home, feeding on shed skin cells. They mainly live in furniture, and are usually harmless. However, their excrement and dead bodies may cause allergic reactions in susceptible people. Magnification: x44 when printed 10 centimetres wide.