Each dust mite has five life stages:
Larva (only six legs)
Protonymph (eight legs from this stage forward)
After hatching from the egg, growth from one stage to the next is achieved by molting (shedding) the outer covering, called the exoskeleton. This “skin” is relatively inflexible and cannot accommodate great increases in the size of the mite. A newly-molted mite has a soft cuticle that briefly allows for an increase in size before it hardens again.
Metamorphosis from egg to adult takes about one month, possibly shorter depending on temperature and humidity. The egg hatches in about one week. The larval stage lasts anywhere from three to ten days. The remaining life stages each take about 4-8 days on the way to adulthood. Aside from adding one pair of legs when they molt from larvae to protonymphs, dust mites gradually reach sexual maturity, the defining characteristic of the adult mite.
Protonymphs, tritonymphs, and adults have both an active and inactive period. Even though mites in all stages of the life cycle can be present throughout the year, the inactive tritonymphs are the mites most likely to survive the decline in humidity that occurs over the winter. They then become active again in spring, molting into adults.
Dust mites reproduce sexually, like most other kinds of animals. Male mites are very anxious to do so and a male may attach himself to a tritonymph female so as to be their when she molts and becomes an adult. Males have enlarged first and third pairs of legs, and a pair of ventral sucker-like organs on their bodies, the better to grasp the female.
Each female dust mite is capable of laying forty to eighty eggs in her one to three month lifespan as an adult. Thus, while dust mites are short-lived by human standards, they also reproduce rapidly and cause allergies that are treated by using encasing your mattress with a dust mite cover.
Dust mites grow by feeding almost exclusively on the shed skin cells of mammals, especially humans. However, they need the help of a fungus to reduce the fat content of the skin cells before the mites can consume it.