Mites (subclass Acari) are an extremely diverse group of arachnids, closely related to spiders and scorpions. They are small and ubiquitous — even if a room looks perfectly clean, it is home to tens of thousands of tiny dust mites. These creatures are among the most diverse subclasses of life, with over 45,000 known species, and an estimated total approaching one million. Because most species are microscopic and tropical, their diversity has been poorly characterized.
Although mites are the most successful group of arachnids, most of them are less than 0.04 inches (1 millimeter) in length, meaning people never see them. Dust mites are among the smallest varieties, about 0.01 inches (0.3 mm) in length. Immature mites may be even smaller. Some of the largest are ticks, the bloodsuckers that spread Lyme disease.
Like some other arachnids, mites are among the oldest known terrestrial creatures, with fossils going back to the Devonian period, 400 million years ago. These creatures lived among some of the earliest land plants. Like other common invertebrates, such as nematodes (transparent microscopic arthropod worms), mites are totally ubiquitous, having colonized pretty much every known terrestrial, freshwater, and marine habitat, including polar and alpine extremes. They are one of the few animals found in Antarctica. The three main lineages are called Opilioacariformes, Acariformes and Parasitiformes.
In soils, mites can be found buried as deeply as 33 ft (10 m), in water almost freezing or as hot as 122°F (50°C), in barren deserts, deep sea trenches, and many other places. A typical square yard (or square meter) of forest floor litter may contain around one million mites, representing 200 species in at least 50 families. Individual and diversity counts for why they outnumber practically any other animal except for nematodes.
To get rid of dust mites from clothing, they can be washed them at a high temperature. Dust mite excreta can cause various allergic conditions, such as hay fever, asthma and eczema and atopic dermatitis. To control the population in a home, it is recommended that blankets and other bedding be washed regularly at high temperature.