Dust mite. Colored Scanning Electron Micrograph (SEM) of a single dust mite Dermatophagoides pteronyssinus. The mouth parts are adapted to feeding on dead scales of human skin found in household dust. Dust mites are related to spiders and scorpions. Their small size makes them invisible to the naked eye. Millions of dust mites live in furniture and fabric in the average home. Their dead bodies and excrement can cause asthma and allergic reactions to household dust.