Mites

Spider mites (Tetranychidae) feed exclusively on plants. They are perhaps the most important agricultural and garden pests worldwide. Some researchers estimate that spider mites reduce total agricultural production by up to 5% each year.

Eriophyid mites (Eriophyidae) are tiny, nearly microscopic mites called leaf vagrants, bud mites and gall mites. Most cause their plant hosts to produce a gall of abnormal tissue on which the mites feed. Some cause extreme leaf deformity. They are distinguished from other mites by having only two pair of legs as adults.

Phytoseiid mites (Phytoseiidae) don't feed on plants but rather are predators of spider mites and other small plant feeding mites. When using pesticides it is important not to eliminate phytoseiid mites which keep other pests in check.

Mites that bite or cause an allergy

Ticks (Ixodidae & Argasidae) are exclusively ectoparasitic mites that feed on the blood of amphibians, reptiles, birds and mammals. They are extremely important as vectors of certain human diseases like Lyme Disease and many others (see Ticks). There are also some small mites that bite and cause skin lesions but they occur in very specific habitats such as near bird and rodent nests (see What are Bird/Rodent/Nest Mites?).

Dust mites (Acaridae: Dermatophagoides) are very closely related to grain mites but feed on shed skin cells rather than fungi. Dust mites are important because they produce allergens in their droppings to which some people are highly allergic. Grain mites (Acaridae: Tyrophagus) are somewhat misnamed since they really feed on the fungi that grows on damp grain and in other damp situations. They can be very important household and warehouse pests. When present in high numbers grain mites can cause allergic reactions in some people as well (see Reducing Dust Mite Allergens in Homes).

Finally some tiny mites specialize in feeding on the skin of warm-blooded animals, including us, rather than blood as ticks do. Chigger mites are the larval (six-legged) stage of a predator mite but feed on skin cells and cause a very itchy rash; they do not burrow into the skin. Mange and scabies mites, on the other hand, actually burrow into the skin causing a very irritating condition. Mange is the condition when it occurs in animals and scabies is the condition in humans (see Scabies Mites in humans and in animals Mange Mites in Animals).

What is Lyme Disease?

What are Chigger Mites?

Mites That Bite Guide