Mites, along with ticks, belong to the subclass Acarina (also known as Acari) and the class Arachnida. Mites are among the most diverse and successful of all the invertebrate groups. They have exploited an incredible array of habitats, and because of their small size most go totally unnoticed.
There are over 45,000 described species of mites. Scientists believe that we have only found 5% of the total diversity of mites. Mites are believed to have existed for around 400 million years.
Mites' life cycle has four basic stages: egg, larva, nymph and adult. The egg hatches into a larval stage, which molts to the nymphal stage. After 1-2 more times, the nymph matures into an adult. Mites, like ticks, have three pairs of legs as larvae and four pairs of legs as nymphs and adults.
The majority of mites are free-living, but thousands of species are parasites of animals and plants. Most of these are external parasites, but some species inhabit the ear canals, lungs, intestine and bladder of vertebrates, particularly domestic animals. Their biting and bloodsucking behavior causes considerable discomfort, and a few species also cause serious allergic reactions, such as asthma, in people. Because of their relatively small size, mites are often the "suspects" of a whole range of biting/itching problems. Understanding their biology and the symptoms associated with mites can help determine if they are the cause of a particular problem.