The largest individuals are the females that measure about 1/64th of an inch. Microscopic examination reveals that the mature mites have eight legs, while the pre-adult stages have six (larva) and eight (protonymph, tritonymph).

Because of the house dust mites' minute size, distribution data is not as readily available as for larger pests. Typically found in beds, pillows, sofas and other soft furnishings and carpets, their presence has been established across the US.

Mites feed on organic matter in house dust, which consists predominantly of human skin scales and also of fungi and food or waste particles. Mites absorb moisture through their skin, so higher relative humidity favor mite population growth (and low humidity limits their distribution.) It is likely that wherever a reasonable level of humidity is maintained, dust mites will be found. Dust mites have been found in mattresses at the rate of up to 12,000 mites per gram. The average life span of the dust mite is 80 days, during which the mature female lays 1-2 eggs per day. At 80 degrees Fahrenheit and 75% relative humidity, development from egg to adult takes about 30 days.