Avid is a miticide that contains Abamectin, which is a mixture of avermectins, which are antibiotic compounds derived from the soil bacterium Streptomyces avermitilis. Abamectin acts as an insecticide by affecting the nervous system of and paralyzing insects. Abamectin is used to control insect and mite pests of citrus, pear, and nut tree crops, and it is used by homeowners for control of fire ants.
Avid is mixed with water and sprayed on the surface of the leaves. It is generally mixed at a rate of 1/4 teaspoon per quart of water. The conventional wisdom is that it is safe to spray on your plants 5 weeks before harvest. Mites die when they come in contact with it.
Avid breaks down quickly once it is mixed so don't mix more of it than you need at the time. Given its cost, that should be an easy caveat with which to live. Do not resuse your leftovers, at its diluted stregnth spider mites may survive a treatment, which might lead to resistance.
Avid is post a pesticide and an ovicide, which means it kills mites and eggs.